Introduction to World Geography

Introduction to World Geography

R. Adam Dastrup

Introduction to World Geography

Icon for the Creative Commons Attribution 4.0 International License

Introduction to World Geography by R. Adam Dastrup is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Publisher Information


This book is adapted from work produced and distributed under a Creative Commons license (CC BY) in 2019 by R. Adam Dastrup, Introduction to Physical Geography and Introduction to Human Geography. This adapted edition is produced by Howard Community College.

This adaptation has altered or updated the original 2019 text with additions adapted from Introduction to Human Geography published by Dorrell, David; Henderson, Joseph; Lindley, Todd; and Connor, Georgeta, “Introduction to Human Geography” (2019). Geological Sciences and Geography Open Textbooks. 2. Copyright 2018 by University System of Georgia, produced and distributed under a Creative Commons Attribution License 4.0 license.

Chapter 1 Introduction to Geography - for print only


Most individuals define geography as a field of study that deals with maps, yet this definition is only partially correct. A better definition of geography may be the study of natural and human-constructed phenomena relative to a spatial dimension.

The Greek word geographos from which geography is derived, is literally translated as writing (graphos) about the Earth (geo). Geography differs from the discipline of geology because geology focuses mainly on the physical Earth and the processes that formed and continue to shape it. On the other hand, geography involves a much broader approach to examining the Earth, as it involves the study of humans as well. As such, geography has two major subdivisions, human (social science) and physical (natural science).

Physical Geography is the study of our home planet and all of its components: its lands, waters, atmosphere, and interior. In this book, some chapters are devoted to the processes that shape the lands and impact people. Other chapters depict the processes of the atmosphere and its relationship to the planet’s surface and all our living creatures. For as long as people have been on the planet, humans have had to live within Earth’s boundaries. Now human life is having a profound effect on the planet. Several chapters are devoted to the effect people have on the planet. Human geography is a social science that focuses on people, where they live, their ways of life, and their interactions in different places around the world. A simple example of a geographic study in human geography would be where is the Hispanic population concentrated in the U.S., and why?

The journey to better understanding Earth begins here with an exploration of how scientists learn about the natural world, along with understanding the science of geography.

Image 1: Bathemetic data from NOAA (

1.1 Scientific Inquiry

Science is a path to gaining knowledge about the natural world. The study of science also includes the body of knowledge that has been collected through scientific inquiry. Scientists conduct scientific investigations by asking testable questions that can be systematically observed and careful evidenced collected. Then they use logical reasoning and some imagination to develop a testable idea, called a hypothesis, along with explanations to explain the idea. Finally, scientists design and conduct experiments based on their hypotheses.

Science seeks to understand the fundamental laws and principles that cause natural patterns and govern natural processes. It is more than just a body of knowledge; science is a way of thinking that provides a means to evaluate and create new knowledge without bias. At its best, science uses objective evidence over subjective evidence to reach sound and logical conclusions.

Truth in science is a difficult concept, and this is because science is falsifiable, which means an initial explanation (hypothesis) is testable and able to be proven false. A scientific theory can never completely be proven correct; it is only after exhaustive attempts to falsify competing for ideas and variations that the theory is assumed to be true. While it may seem like a weakness, the strength behind this is that all scientific ideas have stood up to scrutiny, which is not necessarily true for non-scientific ideas and procedures. In fact, it is the ability to prove current ideas wrong that is a driving force in science and has driven many scientific careers.

Early Scientific Thought

Western science began in ancient Greece, specifically Athens, and early democracies like Athens encouraged individuals to think more independently than the in past when kings ruled most civilizations. Foremost among these early philosopher/scientists was Aristotle, born in 384 B.C.E., who contributed to foundations of knowledge and science. Aristotle was a student of Plato and a tutor to Alexander the Great, who would conquer the Persian Empire as far as India, spreading Greek culture in the process. Aristotle used deductive reasoning, applying what he thought he knew to establish a new idea (if A, then B).

Deductive reasoning starts with generalized principles or established or assumed knowledge and extends them to new ideas or conclusions. If a deductive conclusion is derived from sound principles, then the conclusion has a high degree of certainty. This contrasts with inductive reasoning which begins from new observations and attempts to discern the underlying principles that explain the observations. Inductive reasoning relies on evidence to infer a conclusion and does not have the perceived certainty of deductive reasoning. Both are important in science. Scientists take existing principles and laws and see if these explain observations. Also, they make new observations and seek to determine the principles and laws that underlie them. Both emphasize the two most important aspects of science: observations and inferences.

An elder Plato walks alongside Aristotle.

Greek culture was absorbed by the Romans. The Romans controlled people and resources in their Empire by building an infrastructure of roads, bridges, and aqueducts. Their road network helped spread Greek culture and knowledge throughout the Empire. The fall of the Roman Empire ushered in the Medieval period in Europe in which scientific progress in Europe was largely overlooked. During Europe’s Medieval period, science flourished in the Middle East between 800 and 1450 CE as the Islamic civilization developed. Empirical experimentation grew during this time and was a key component of the scientific revolution that started in 17th century Europe. Empiricism emphasizes the value of evidence gained from experimentation and observations of the senses. Because of the respect, others hold for Aristotle’s wisdom and knowledge, his logical approach was accepted for centuries and formed an essential basis for understanding nature. The Aristotelian approach came under criticism by 17th-century scholars of the Renaissance.

As science progressed, certain aspects of science that could not be experimented and sensed awaited the development of new technologies, such as atoms, molecules, and the deep-time of geology. The Renaissance, following the Medieval period between the fourteenth and seventeenth centuries, was a great awakening of artistic and scientific thought and expression in Europe.

The foundational example of the modern scientific approach is the understanding of the solar system. The Greek astronomer Claudius Ptolemy, in the second century, using an Aristotelian approach and mathematics, observed the Sun, Moon, and stars moving across the sky and deductively reasoned that Earth must be at the center of the universe with the celestial bodies circling Earth. Ptolemy even had mathematical, astronomical calculations that supported his argument. The view of the cosmos with Earth at its center is called the geocentric model.

In contrast, early Renaissance scholars used new instruments such as the telescope to enhance astronomical observations and developed new mathematics to explain those observations. These scholars proposed a radically new understanding of the cosmos, one in which Earth and the other planets orbited around the centrally located Sun. This is known as the heliocentric model, and astronomer Nicolaus Copernicus (1473-1543) was the first to offer a solid mathematical explanation for it around 1543.

1.2 Geographic Inquiry

Geography is the study of the physical and cultural environments of the earth. What makes geography different from other disciplines is its focus on spatial inquiry and analysis. Geographers also try to look for connections between things such as patterns, movement and migration, trends, and so forth. This process is called a geographic or spatial inquiry. To do this, geographers go through a geographic methodology that is quite similar to the scientific method, but again with a geographic or spatial emphasis. This method can be simplified as the geographic inquiry process.

“Knowing where something is, how its location influences its characteristics, and how its location influences relationships with other phenomena are the foundation of geographic thinking. This mode of investigation asks you to see the world and all that is in it in spatial terms. Like other research methods, it also asks you to explore, analyze, and act upon the things you find. It is also important to recognize that this is the same method used by professionals around the world working to address social, economic, political, environmental, and a wide-range of other scientific issues.” (ESRI).

1.3 History of Geography

Some of the first genuinely geographical studies occurred more than four thousand years ago. The primary purpose of these early investigations was to map features and places observed as explorers traveled to new lands. At this time, Chinese, Egyptian, and Phoenician civilizations were beginning to explore the places and spaces within and outside of their homelands. The earliest evidence of such explorations comes from the archaeological discovery of a Babylonian clay tablet map that dates back to 2300 BC.

The early Greeks were the first civilization to practice a form of geography that was more than just map-making or cartography. Greek philosophers and scientist were also interested in learning about spatial nature of human and physical features found on the Earth. One of the first Greek geographers was Herodotus (circa 484 – 425 BC). Herodotus wrote some volumes that described the human and physical geography of the various regions of the Persian Empire.

The ancient Greeks were also interested in the form, size, and geometry of the Earth. Aristotle (circa 384 – 322 BC) hypothesized and scientifically demonstrated that the Earth had a spherical shape. Evidence for this idea came from observations of lunar eclipses. Lunar eclipses occur when the Earth casts its circular shadow on to the moon’s surface. The first individual to accurately calculate the circumference of the Earth was the Greek geographer Eratosthenes (circa 276 – 194 BC). Eratosthenes calculated the equatorial circumference to be 40,233 kilometers using simple geometric relationships. This first calculation was unusually accurate. Measurements of the Earth using modern satellite technology have computed the circumference to be 40,072 kilometers.

Illustration showing a portion of the globe showing a part of the African continent. The sunbeams shown as two rays hitting the ground at Syene and Alexandria. Angle of sunbeam and the gnomons (vertical pole) is shown at Alexandria, which allowed Eratosthenes’ estimates of radius and circumference of Earth.

Most of the Greek accomplishments in geography were passed on to the Romans. Roman military commanders and administrators used this information to guide the expansion of their Empire. The Romans also made several notable additions to geographical knowledge. Strabo (circa 64 BC – 20 AD) wrote a 17 volume series called “Geographia.” Strabo claimed to have traveled widely and recorded what he had seen and experienced from a geographical perspective. In his series of books, Strabo describes the cultural geographies of the various societies of people found from Britain to as far east as India and south to Ethiopia and as far north as Iceland. Strabo also suggested a definition of geography that is quite complementary to the way many human geographers define their discipline today. This definition suggests that geography aimed to “describe the known parts of the inhabited world… to write the assessment of the countries of the world [and] to treat the differences between countries.”

During the second century AD, Ptolemy (circa 100 – 178 AD) made some important contributions to geography. Ptolemy’s publication Geographike hyphegesis or “Guide to Geography” compiled and summarize much of the Greek and Roman geographic information accumulated at that time. Some of his other notable contributions include the creation of three different methods for projecting the Earth’s surface on a map, the calculation of coordinate locations for some eight thousand places on the Earth, and development of the concepts of geographical latitude and longitude.

A 15th-century manuscript copy of the Ptolemy world map, reconstituted from Ptolemy’s Geography (circa AD 150), indicating the countries of “Serica” and “Sinae” (China) at the extreme east, beyond the island of “Taprobane” (Sri Lanka, oversized) and the “Aurea Chersonesus” (Malay Peninsula).

Little academic progress in geography occurred after the Roman period. For the most part, the Middle Ages (5th to 13th centuries AD) were a time of intellectual stagnation. In Europe, the Vikings of Scandinavia were the only group of people carrying out active exploration of new lands. In the Middle East, Arab academics began translating the works of Greek and Roman geographers starting in the 8th century and began exploring southwestern Asia and Africa. Some of the essential intellectuals in Arab geography were Al-Idrisi, Ibn Battutah, and Ibn Khaldun. Al-Idrisi is best known for his skill at making maps and for his work of descriptive geography Kitab nuzhat al-mushtaq fi ikhtiraq al-afaq or “The Pleasure Excursion of One Who Is Eager to Traverse the Regions of the World.” Ibn Battutah and Ibn Khaldun are well known for writing about their extensive travels of North Africa and the Middle East.

During the Renaissance (1400 to 1600 AD) numerous journeys of geographical exploration were commissioned by a variety of nation-states in Europe. Most of these voyages were financed because of the potential commercial returns from resource exploitation. The voyages also provided an opportunity for scientific investigation and discovery. These voyages also added many significant contributions to geographic knowledge. Important explorers of this period include Christopher Columbus, Vasco da Gama, Ferdinand Magellan, Jacques Cartier, Sir Martin Frobisher, Sir Francis Drake, John and Sebastian Cabot, and John Davis. Also during the Renaissance, Martin Behaim created a spherical globe depicting the Earth in its true three-dimensional form in 1492. Behaim’s invention was a significant advance over two-dimensional maps because it created a more realistic depiction of the Earth’s shape and surface configuration.

In the 17th century, Bernhardus Varenius (1622-1650) published an important geographic reference titled Geographia generalis (General Geography: 1650). In this volume, Varenius used direct observations and primary measurements to present some new ideas concerning geographic knowledge. This work continued to be a standard geographic reference for about a 100 years. Varenius also suggested that the discipline of geography could be subdivided into three distinct branches. The first branch examines the form and dimensions of the Earth. The second sub-discipline deals with tides, climatic variations over time and space, and other variables that are influenced by the cyclical movements of the Sun and moon. Together these two branches form the early beginning of what we collectively now call physical geography. The last branch of geography examined distinct regions on the Earth using comparative cultural studies. Today, this area of knowledge is called cultural geography.

During the 18th century, the German philosopher Immanuel Kant (1724-1804) proposed that human knowledge could be organized in three different ways. One way of organizing knowledge was to classify its facts according to the type of objects studied. Accordingly, zoology studies animals, botany examines plants, and geology involves the investigation of rocks. The second way one can study things is according to a temporal dimension. This field of knowledge is, of course, called history. The last method of organizing knowledge involves understanding facts relative to spatial relationships. This field of knowledge is commonly known as geography. Kant also divided geography into some sub-disciplines. He recognized the following six branches: Physical, mathematical, moral, political, commercial, and theological geography.

Geographic knowledge saw strong growth in Europe and the United States in the 1800s. This period also saw the emergence of a number of societies interested in geographic issues. In Germany, Alexander von Humboldt, Carl Ritter, and Fredrich Ratzel made substantial contributions to human and physical geography. Humboldt’s publication Kosmos (1844) examines the geology and physical geography of the Earth. This work is considered by many academics to be a milestone contribution to geographic scholarship. Late in the 19th Century, Ratzel theorized that the distribution and culture of the Earth’s various human populations were strongly influenced by the natural environment. The French geographer Paul Vidal de la Blanche opposed this revolutionary idea. Instead, he suggested that human beings were a dominant force shaping the form of the environment. The idea that humans were modifying the physical environment was also prevalent in the United States. In 1847, George Perkins Marsh gave an address to the Agricultural Society of Rutland County, Vermont. The subject of this speech was that human activity was having a destructive impact on the land, primarily through deforestation and land conversion. This speech also became the foundation for his book Man and Nature or The Earth as Modified by Human Action, first published in 1864. In this publication, Marsh warned of the ecological consequences of the continued development of the American frontier.

During the first 50 years of the 1900s, many academics in the field of geography extended the various ideas presented in the previous century to studies of small regions all over the world. Most of these studies used descriptive field methods to test research questions. Starting around 1950, geographic research experienced a shift in methodology. Geographers began adopting a more scientific approach that relied on quantitative techniques. The quantitative revolution was also associated with a change in the way in which geographers studied the Earth and its phenomena. Researchers now began investigating process rather than a mere description of the event of interest. Today, the quantitative approach is becoming even more prevalent due to advances in computer and software technologies.

In 1964, William Pattison published an article in the Journal of Geography (1964, 63: 211-216) that suggested that modern Geography was now composed of the following four academic traditions:

Today, the academic traditions described by Pattison are still dominant fields of geographical investigation. However, the frequency and magnitude of human-mediated environmental problems have been on a steady increase since the publication of this notion. These increases are the result of a growing human population and the consequent increase in the consumption of natural resources. As a result, an increasing number of researchers in geography are studying how humans modify the environment. A significant number of these projects also develop strategies to reduce the negative impact of human activities on nature. Some of the dominant themes in these studies include environmental degradation of the hydrosphere, atmosphere, lithosphere, and biosphere; resource use issues; natural hazards; environmental impact assessment; and the effect of urbanization and land-use change on natural environments.

Considering all of the statements presented concerning the history and development of geography, we are now ready to formulate a somewhat coherent definition. This definition suggests that geography, in its purest form, is the field of knowledge that is concerned with how phenomena are spatially organized. Physical geography attempts to determine why natural phenomena have particular spatial patterns and orientation. This online textbook will focus primarily on the Earth Science Tradition. Some of the information that is covered in this textbook also deals with the alterations of the environment because of human interaction. These pieces of information belong in the Human-Land Tradition of geography.

1.4 Elements of Geography

Geography is a discipline that integrates a wide variety of subject matter. Almost any area of human knowledge can be examined from a spatial perspective. Physical geography’s primary subdisciplines study the Earth’s atmosphere (meteorology and climatology), animal and plant life (biogeography), physical landscape (geomorphology), soils (pedology), and waters (hydrology). Some of the principal areas of study in human geography include human society and culture (social and cultural geography), behavior (behavioral geography), economics (economic geography), politics (political geography), and urban systems (urban geography).

Holistic synthesis connects knowledge from a variety of academic fields in both human and physical geography. For example, the study of the enhancement of the Earth’s greenhouse effect and the resulting global warming requires a multidisciplinary approach for complete understanding. The fields of climatology and meteorology are required to understand the physical effects of adding additional greenhouse gases to the atmosphere’s radiation balance. The field of economic geography provides information on how various forms of human economic activity contribute to the emission of greenhouse gases through fossil fuel burning and land-use change. Combining the knowledge of both of these academic areas gives us a more comprehensive understanding of why this environmental problem occurs.

The holistic nature of geography is both a strength and a weakness. Geography’s strength comes from its ability to connect functional interrelationships that are not generally noticed in narrowly defined fields of knowledge. The most apparent weakness associated with the geographical approach is related to the fact that holistic understanding is often too simple and misses essential details of cause and effect.


Dreifus, C. Naomi Oreskes Imagines the Future History of Climate Change. The New York Times(2014).
Science literacy: concepts, contexts, and consequences. (National Academies Press (US), 2016).
Shermer, M. What Is Pseudoscience? Scientific American (2011).
Railsback, B. L. T. C. Chamberlin’s “Method of Multiple Working Hypotheses”: An encapsulation for modern students. Houston Geological Society Bulletin 47, 68–69 (2004).
Martin, C. Subverting Aristotle: Religion, History, and Philosophy in Early Modern Science. (Baltimore : Johns Hopkins University Press., 2014).
Marshall, J. A short history of Greek philosophy. (Andrews UK Limited, 2010).
Saliba, G. Islamic science and the making of the European renaissance. (MIT Press, 2007).
Hogendijk, J. P. & Sabra, A. I. The Enterprise of Science in Islam: New Perspectives. (MIT Press, 2003).
Beckwith, C. How western Europe developed a full scientific method. Berfrois (2013).
Goldstein, B. R. Copernicus and the origin of his heliocentric system. Journal for the History of Astronomy 33, 219–235 (2002).
Repcheck, J. Copernicus’ secret: How the scientific revolution began. (Simon and Schuster, 2007).
Kolbert, E. The sixth extinction: an unnatural history. (Henry Holt and Co., 2014).
Bocking, S. Nature’s experts: science, politics, and the environment. (Rutgers University Press, 2004).

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Chapter 2 Techniques of Geographic Analysis for print only


A map can be defined as a graphic representation of the real world. Because of the infinite nature of our Universe, it is impossible to capture all of the complexity found in the real world. For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of paper.

Maps are used to display both cultural and physical features of the environment. Standard topographic maps show a variety of information including roads, land-use classification, elevation, rivers and other water bodies, political boundaries, and the identification of houses and other types of buildings. Some maps are created with particular goals in mind, with an intended purpose.

2.1 Understanding Maps

Most maps allow us to specify the location of points on the Earth’s surface using a coordinate system. For a two-dimensional map, this coordinate system can use simple geometric relationships between the perpendicular axes on a grid system to define spatial location. Two types of coordinate systems are currently in general use in geography: the geographical coordinate system and the rectangular (also called Cartesian) coordinate system.

The United States population density map based on Census 2010 data.

Geographical Coordinate System

The geographical coordinate system measures location from only two values, despite the fact that the locations are described for a three-dimensional surface. The two values used to define location are both measured relative to the polar axis of the Earth. The two measures used in the geographic coordinate system are called latitude and longitude.

Latitude is an angular measurement north or south of the equator relative to a point found at the center of the Earth. This central point is also located on the Earth’s rotational or polar axis. The equator is the starting point for the measurement of latitude. The equator has a value of zero degrees. A line of latitude or parallel of 30° North has an angle that is 30° north of the plane represented by the equator. The maximum value that latitude can attain is either 90° North or South. These lines of latitude run parallel to the rotational axis of the Earth.

Lines connecting points of the same latitude, called parallels, has lines running parallel to each other. The only parallel that is also a great circle is the equator. All other parallels are small circles. The following are the most important parallel lines:

Longitude is the angular measurement east and west of the Prime Meridian. The position of the Prime Meridian was determined by international agreement to be in-line with the location of the former astronomical observatory at Greenwich, England. Because the Earth’s circumference is similar to a circle, it was decided to measure longitude in degrees. The number of degrees found in a circle is 360. The Prime Meridian has a value of zero degrees. A line of longitude or meridian of 45° West has an angle that is 45° west of the plane represented by the Prime Meridian. The maximum value that a meridian of longitude can have is 180° which is the distance halfway around a circle. This meridian is called the International Date Line. Designations of west and east are used to distinguish where a location is found relative to the Prime Meridian. For example, all of the locations in North America have a longitude that is designated west.

At 180 degrees of the Prime Meridian in the Pacific Ocean is the International Date Line. The line determines where the new day begins in the world. Now because of this, the International Date Line is not a straight line, rather it follows national borders so that a country is not divided into two separate days.

Ultimately, when parallel and meridian lines are combined, the result is a geographic grid system that allows users to determine their exact location on the planet.

This may be an appropriate time to briefly discuss the fact that the earth is round and not flat.

Great and Small Circles


A great circle divides the sphere in two equal hemispheres.

Much of Earth’s grid system is based on the location of the North Pole, South Pole, and the Equator. The poles are an imaginary line running from the axis of Earth’s rotation. The plane of the equator is an imaginary horizontal line that cuts the earth into two halves. This brings up the topic of great and small circles. A great circle is any circle that divides the earth into a circumference of two halves. It is also the largest circle that can be drawn on a sphere. The line connecting any points along a great circle is also the shortest distance between those two points.


Examples of great circles include the Equator, all lines of longitude, the line that divides the earth into day and night called the circle of illumination, and the plane of the ecliptic, which divides the earth into equal halves along the equator. Small circles are circles that cut the earth, but not into equal halves.

Universal Transverse Mercator System (UTM)

Another commonly used method to describe a location on the Earth is the Universal Transverse Mercator (UTM) grid system. This rectangular coordinate system is metric, incorporating the meter as its basic unit of measurement. UTM also uses the Transverse Mercator projection system to model the Earth’s spherical surface onto a two-dimensional plane. The UTM system divides the world’s surface into 60, six-degree longitude-wide zones that run north-south. These zones start at the International Date Line and are successively numbered in an eastward direction. Each zone stretches from 84° North to 80° South. In the center of each of these zones is a central meridian.

Location is measured in these zones from a false origin, which is determined relative to the intersection of the equator and the central meridian for each zone. For locations in the Northern Hemisphere, the false origin is 500,000 meters west of the central meridian on the equator. Coordinate measurements of location in the Northern Hemisphere using the UTM system are made relative to this point in meters in eastings (longitudinal distance) and northings (latitudinal distance). The point defined by the intersection of 50° North and 9° West would have a UTM coordinate of Zone 29, 500000 meters east (E), 5538630 meters north (N). In the Southern Hemisphere, the origin is 10,000,000 meters south and 500,000 meters west of the equator and central meridian, respectively. The location found at 50° South and 9° West would have a UTM coordinate of Zone 29, 500000 meters E, 4461369 meters N (remember that northing in the Southern Hemisphere is measured from 10,000,000 meters south of the equator).

Universal Transverse Mercator zones for the entire world.

The UTM system has been modified to make measurements less confusing. In this modification, the six degree wide zones are divided into smaller pieces or quadrilaterals that are eight degrees of latitude tall. Each of these rows is labeled, starting at 80° South, with the letters C to X consecutively with I and O being omitted. The last row X differs from the other rows and extends from 72 to 84° North latitude (twelve degrees tall). Each of the quadrilaterals or grid zones are identified by their number/letter designation. In total, 1200 quadrilaterals are defined in the UTM system.

The quadrilateral system allows us to define location further using the UTM system. For the location 50° North and 9° West, the UTM coordinate can now be expressed as Grid Zone 29U, 500000 meters E, 5538630 meters N.

Each UTM quadrilateral is further subdivided into a number of 100,000 by 100,000-meter zones. These subdivisions are coded by a system of letter combinations where the same two-letter combination is not repeated within 18 degrees of latitude and longitude. Within each of the 100,000-meter squares, one can specify a location to one-meter accuracy using a five-digit eastings and northings reference system.

The UTM grid system is displayed on all United States Geological Survey (USGS) and National Topographic Series (NTS) of Canada maps. On USGS 7.5-minute quadrangle maps (1:24,000 scale), 15-minute quadrangle maps (1:50,000, 1:62,500, and standard-edition 1:63,360 scales), and Canadian 1:50,000 maps the UTM grid lines are drawn at intervals of 1,000 meters. Both are shown either with blue ticks at the edge of the map or by full blue grid lines. On USGS maps at 1:100,000 and 1:250,000 scale and Canadian 1:250,000 scale maps a full UTM grid is shown at intervals of 10,000 meters.

2.2 Time Zones

Before the late nineteenth century, timekeeping was primarily a local phenomenon. Each town would set their clocks according to the motions of the Sun. Noon was defined as the time when the Sun reached its maximum altitude above the horizon. Cities and towns would assign a clockmaker to calibrate a town clock to these solar motions. This town clock would then represent “official” time, and the citizens would set their watches and clocks accordingly.

The ladder half of the nineteenth century was a time of increased movement of humans. In the United States and Canada, large numbers of people were moving west and settlements in these areas began expanding rapidly. To support these new settlements, railroads moved people and resources between the various cities and towns. However, because of the nature of how local time was kept, the railroads experience significant problems in constructing timetables for the various stops. Timetables could only become more efficient if the towns and cities adopted some standard method of keeping time.

In 1878, Canadian Sir Sanford Fleming suggested a system of worldwide time zones that would simplify the keeping of time across the Earth. Fleming proposed that the globe should be divided into 24 time zones, every 15 degrees of longitude in width. Since the world rotates once every 24 hours on its axis and there are 360 degrees of longitude, each hour of Earth rotation represents 15 degrees of longitude.

Railroad companies in Canada and the United States began using Fleming’s time zones in 1883. In 1884, an International Prime Meridian Conference was held in Washington D.C. to adopt the standardized method of timekeeping and determined the location of the Prime Meridian. Conference members agreed that the longitude of Greenwich, England would become zero degrees longitude and established the 24 time zones relative to the Prime Meridian. It was also proposed that the measurement of time on the Earth would be made relative to the astronomical measurements at the Royal Observatory at Greenwich. This time standard was called Greenwich Mean Time (GMT).

Standard time zones of the world based on the public domain map created by the CIA.

Today, many nations operate on variations of the time zones suggested by Sir Fleming. In this system, time in the various zones is measured relative the Coordinated Universal Time (UTC) standard at the Prime Meridian. Coordinated Universal Time became the standard legal reference of time all over the world in 1972. UTC is determined from atomic clocks that are coordinated by the International Bureau of Weights and Measures (BIPM) located in France. The numbers located at the bottom of the time zone map indicate how many hours each zone is earlier (negative sign) or later (positive sign) than the Coordinated Universal Time standard. Also, note that national boundaries and political matters influence the shape of the time zone boundaries. For example, China uses a single time zone (eight hours ahead of Coordinated Universal Time) instead of five different time zones.

2.3 Coordinate Systems and Projections

Distance on Maps

Depicting the Earth’s three-dimensional surface on a two-dimensional map creates a variety of distortions that involve distance, area, and direction. It is possible to create maps that are somewhat equidistance. However, even these types of maps have some form of distance distortion. Equidistance maps can only control distortion along either lines of latitude or lines of longitude. Distance is often correct on equidistance maps only in the direction of latitude.

On a map that has a large scale, 1:125,000 or larger, distance distortion is usually insignificant. An example of a large-scale map is a standard topographic map. On these maps measuring straight line distance is simple. Distance is first measured on the map using a ruler. This measurement is then converted into a real-world distance using the map’s scale. For example, if we measured a distance of 10 centimeters on a map that had a scale of 1:10,000, we would multiply 10 (distance) by 10,000 (scale). Thus, the actual distance in the real world would be 100,000 centimeters.

Measuring distance along map features that are not straight is a little more difficult. One technique that can be employed for this task is to use several straight-line segments. The accuracy of this method is dependent on the number of straight-line segments used. Another method for measuring curvilinear map distances is to use a mechanical device called an opisometer. This device uses a small rotating wheel that records the distance traveled. The recorded distance is measured by this device either in centimeters or inches.

Direction on Maps

Like distance, direction is difficult to measure on maps because of the distortion produced by projection systems. However, this distortion is quite small on maps with scales larger than 1:125,000. Direction is usually measured relative to the location of North or South Pole. Directions determined from these locations are said to be relative to True North or True South. The magnetic poles can also be used to measure direction. However, these points on the Earth are located in spatially different spots from the geographic North and South Pole. The North Magnetic Pole is located at 78.3° North, 104.0° West near Ellef Ringnes Island, Canada. In the Southern Hemisphere, the South Magnetic Pole is located in Commonwealth Day, Antarctica and has a geographical location of 65° South, 139° East. The magnetic poles are also not fixed over time and shift their spatial position over time.

Topographic maps typically have a declination diagram drawn on them. On Northern Hemisphere maps, declination diagrams describe the angular difference between Magnetic North and True North. On the map, the angle of True North is parallel to the depicted lines of longitude. Declination diagrams also show the direction of Grid North. Grid North is an angle that is parallel to the easting lines found on the Universal Transverse Mercator (UTM) grid system.

In the field, the direction of features is often determined by a magnetic compass which measures angles relative to Magnetic North. Using the declination diagram found on a map, individuals can convert their field measures of magnetic direction into directions that are relative to either Grid or True North. Compass directions can be described by using either the azimuth system or the bearing system. The azimuth system calculates direction in degrees of a full circle. A full circle has 360 degrees. In the azimuth system, north has a direction of either the 0 or 360°. East and West have an azimuth of 90° and 270°, respectively. Due south has an azimuth of 180°.

The bearing system divides direction into four quadrants of 90 degrees. In this system, north and south are the dominant directions. Measurements are determined in degrees from one of these directions.

Geography is about spatial understanding, which requires an accurate grid system to determine absolute and relative location. Absolute location is the exact x- and y- coordinate on the Earth. Relative location is the location of something relative to other entities. For example, when someone uses his or her GPS on his or her smartphone or car, they will put in an absolute location. However, as they start driving, the device tells them to turn right or left relative to objects on the ground.

2.4 Geospatial Technology

Data, data, data… data is everywhere. There are two basic types of data to be familiar with: spatial and non-spatial data. Spatial data, also called geospatial data, is data directly related to a specific location on Earth. Geospatial data is becoming “big business” because it is not just data, but data that can be located, tracked, patterned, and modeled based on other geospatial data. Census information that is collected every ten years is an example of spatial data. Non-spatial data is data that cannot be traced to a specific location, including the number of people living in a household, enrollment within a specific course, or gender information. However, non-spatial data can easily become spatial data if it can connect in some way to a location. Geospatial technology specialists have a method called geocoding that can be used to give non-spatial data a geographic location. Once data has a spatial component associated with it, the type of questions that can be asked dramatically changes.

Remote Sensing

Remote sensing can be defined as the collection of data about an object from a distance. Humans and many other types of animals accomplish this task with the aid of eyes or by the sense of smell or hearing. Geographers use the technique of remote sensing to monitor or measure phenomena found in the Earth’s lithosphere, biosphere, hydrosphere, and atmosphere. Remote sensing of the environment by geographers is usually done with the help of mechanical devices known as remote sensors. These gadgets have a significantly improved ability to receive and record information about an object without any physical contact. Often, these sensors are positioned away from the object of interest by using helicopters, planes, and satellites. Most sensing devices record information about an object by measuring an object’s transmission of electromagnetic energy from reflecting and radiating surfaces.

Thumbnail for the embedded element "What is Remote Sensing?"

A YouTube element has been excluded from this version of the text. You can view it online here:

Remote sensing imagery has many applications in mapping land-use and cover, agriculture, soils mapping, forestry, city planning, archaeological investigations, military observation, and geomorphological surveying, among other uses. For example, foresters use aerial photographs for preparing forest cover maps, locating possible access roads, and measuring quantities of trees harvested. Specialized photography using color infrared film has also been used to detect disease and insect damage in forest trees.

Satellite Remote Sensing

The simplest form of remote sensing uses photographic cameras to record information from visible or near-infrared wavelengths. In the late 1800s, cameras were positioned above the Earth’s surface in balloons or kites to take oblique aerial photographs of the landscape. During World War I, aerial photography played an important role in gathering information about the position and movements of enemy troops. These photographs were often taken from airplanes. After the war, civilian use of aerial photography from airplanes began with the systematic vertical imaging of large areas of Canada, the United States, and Europe. Many of these images were used to construct topographic and other types of reference maps of the natural and human-made features found on the Earth’s surface.

The Loop Current pushes up into the Gulf from the Caribbean Sea. The current’s tropical warmth makes it stand out from the surrounding cooler waters of the Gulf of Mexico in this image. The current loses its northward momentum about mid-way through the gulf, and bends back on itself to flow south. It joins warm waters flowing eastward between Florida and Cuba, which then merge with the Gulf Stream Current on its journey up the East Coast.

The development of color photography following World War II gave a more natural depiction of surface objects. Color aerial photography also substantially increased the amount of information gathered from an object. The human eye can differentiate many more shades of color than tones of gray. In 1942, Kodak developed color infrared film, which recorded wavelengths in the near-infrared part of the electromagnetic spectrum. This film type had good haze penetration and the ability to determine the type and health of vegetation.

In the 1960s, a revolution in remote sensing technology began with the deployment of space satellites. From their high vantage-point, satellites have an extended view of the Earth’s surface. The first meteorological satellite, TIROS-1, was launched by the United States using an Atlas rocket on April 1, 1960. This early weather satellite used vidicon cameras to scan broad areas of the Earth’s surface. Early satellite remote sensors did not use conventional film to produce their images. Instead, the sensors digitally capture the images using a device similar to a television camera. Once captured, this data is then transmitted electronically to receiving stations found on the Earth’s surface.

In the 1970s, the second revolution in remote sensing technology began with the deployment of the Landsat satellites. Since this 1972, several generations of Landsat satellites with their Multispectral Scanners (MSS) have been providing continuous coverage of the Earth for almost 30 years. Current, Landsat satellites orbit the Earth’s surface at an altitude of approximately 700 kilometers. The spatial resolution of objects on the ground surface is 79 x 56 meters. Complete coverage of the globe requires 233 orbits and occurs every 16 days. The Multispectral Scanner records a zone of the Earth’s surface that is 185 kilometers wide in four wavelength bands: band 4 at 0.5 to 0.6 micrometers, band 5 at 0.6 to 0.7 micrometers, band 6 at 0.7 to 0.8 micrometers, and band 7 at 0.8 to 1.1 micrometers. Bands 4 and 5 receive the green and red wavelengths in the visible light range of the electromagnetic spectrum. The last two bands image near-infrared wavelengths. A second sensing system was added to Landsat satellites launched after 1982. This imaging system, known as the Thematic Mapper, records seven wavelength bands from the visible to far-infrared portions of the electromagnetic spectrum. Also, the ground resolution of this sensor was enhanced to 30 x 20 meters. This modification allows for significantly improved clarity of imaged objects.

The usefulness of satellites for remote sensing has resulted in several other organizations launching their own devices. In France, the SPOT (Satellite Pour l’Observation de la Terre) satellite program has launched five satellites since 1986. Since 1986, SPOT satellites have produced more than 10 million images. SPOT satellites use two different sensing systems to image the planet. One sensing system produces black and white panchromatic images from the visible band (0.51 to 0.73 micrometers) with a ground resolution of 10 x 10 meters. The other sensing device is multispectral capturing green, red, and reflected infrared bands at 20 x 20 meters. SPOT-5, which was launched in 2002, is much improved from the first four versions of SPOT satellites. SPOT-5 has a maximum ground resolution of 2.5 x 2.5 meters in both panchromatic mode and multispectral operation.

Radarsat-1 was launched by the Canadian Space Agency in November, 1995. As a remote sensing device, Radarsat is entirely different from the Landsat and SPOT satellites. Radarsat is an active remote sensing system that transmits and receives microwave radiation. Landsat and SPOT sensors passively measure reflected radiation at wavelengths roughly equivalent to those detected by our eyes. Radarsat’s microwave energy penetrates clouds, rain, dust, or haze and produces images regardless of the Sun’s illumination allowing it to image in darkness. Radarsat images have a resolution between 8 to 100 meters. This sensor has found important applications in crop monitoring, defense surveillance, disaster monitoring, geologic resource mapping, sea-ice mapping and monitoring, oil slick detection, and digital elevation modeling.

Today, the GOES (Geostationary Operational Environmental Satellite) system of satellites provides most of the remotely sensed weather information for North America. To cover the entire continent and adjacent oceans, two satellites are employed in a geostationary orbit. The western half of North America and the eastern Pacific Ocean is monitored by GOES-10, which is directly above the equator and 135° West longitude. The eastern half of North America and the western Atlantic are cover by GOES-8. The GOES-8 satellite is located overhead of the equator and 75° West longitude. Advanced sensors aboard the GOES satellite produce a continuous data stream so images can be viewed at any instance. The imaging sensor produces visible and infrared images of the Earth’s terrestrial surface and oceans. Infrared images can depict weather conditions even during the night. Another sensor aboard the satellite can determine vertical temperature profiles, vertical moisture profiles, total precipitable water, and atmospheric stability.

Principles of Object Identification

Most people have no problem identifying objects from photographs taken from an oblique angle. Such views are natural to the human eye and are part of our everyday experience. However, most remotely sensed images are taken from an overhead or vertical perspective and distances quite removed from ground level. Both of these circumstances make the interpretation of natural and human-made objects somewhat difficult. In addition, images obtained from devices that receive and capture electromagnetic wavelengths outside human vision can present views that are quite unfamiliar.

To overcome the potential difficulties involved in image recognition, professional image interpreters use some characteristics to help them identify remotely sensed objects. Some of these characteristics include:

The Uluru/Ayers Rock sandstone rock formation in Australia’s Northern Territory.

Global Positioning Systems

Another type of geospatial technology isglobal positioning systems (GPS) and a key technology for acquiring accurate control points on Earth’s surface. Now to determine the location of that GPS receiver on Earth’s surface, a minimum of four satellites is required using a mathematical process called triangulation. Usually, the process of triangulation requires a minimum of three transmitters, but because the energy sent from the satellite is traveling at the speed of light, minor errors in calculation could result in significant location errors on the ground. Thus, a minimum of four satellites is often used to reduce this error. This process using the geometry of triangles to determine location is used not only in GPS, but a variety of other location needs like finding the epicenter of earthquakes.

How global positioning sytems (GPS) works.

A user can use a GPS receiver to determine their location on Earth through a dynamic conversation with satellites in space. Each satellite transmits orbital information called the ephemeris using a highly accurate atomic clock along with its orbital position called the almanac. The receiver will use this information to determine its distance from a single satellite using the equation D = rt, where D = distance, r = rate or the speed of light (299,792,458 meters per second), and t = time using the atomic clock. The atomic clock is required because the receiver is trying to calculate distance, using energy that is transmitted at the speed of light. Time will be fractions of a second and requires a “time clock” up the utmost accuracy.

Determination of location in field conditions was once a difficult task. In most cases, it required the use of a topographic map and landscape features to estimate location. However, technology has now made this task very simple. Global Positioning Systems (GPS) can calculate one’s location to an accuracy of about 30-meters. These systems consist of two parts: a GPS receiver and a network of many satellites. Radio transmissions from the satellites are broadcasted continually. The GPS receiver picks up these broadcasts and through triangulation calculates the altitude and spatial position of the receiving unit. A minimum of three satellite is required for triangulation.

GPS receivers can determine latitude, longitude, and elevation anywhere on or above the Earth’s surface from signals transmitted by a number of satellites. These units can also be used to determine direction, distance traveled, and determine routes of travel in field situations.

Geographic Information Systems

The advent of cheap and powerful computers over the last few decades has allowed for the development of innovative software applications for the storage, analysis, and display of geographic data. Many of these applications belong to a group of software known as Geographic Information Systems (GIS). Many definitions have been proposed for what constitutes a GIS. Each of these definitions conforms to the particular task that is being performed. A GIS does the following activities:

The first computerized GIS began its life in 1964 as a project of the Rehabilitation and Development Agency Program within the government of Canada. The Canada Geographic Information System (CGIS) was designed to analyze Canada’s national land inventory data to aid in the development of land for agriculture. The CGIS project was completed in 1971, and the software is still in use today. The CGIS project also involved a number of key innovations that have found their way into the feature set of many subsequent software developments.

From the mid-1960s to 1970s, developments in GIS were mainly occurring at government agencies and universities. In 1964, Howard Fisher established the Harvard Lab for Computer Graphics where many of the industries early leaders studied. The Harvard Lab produced a number of mainframe GIS applications including SYMAP (Synagraphic Mapping System), CALFORM, SYMVU, GRID, POLYVRT, and ODYSSEY. ODYSSEY was first modern vector GIS, and many of its features would form the basis for future commercial applications. Automatic Mapping System was developed by the United States Central Intelligence Agency (CIA) in the late 1960s. This project then spawned the CIA’s World Data Bank, a collection of coastlines, rivers, and political boundaries, and the CAM software package that created maps at different scales from this data. This development was one of the first systematic map databases. In 1969, Jack Dangermond, who studied at the Harvard Lab for Computer Graphics, co-founded Environmental Systems Research Institute (ESRI) with his wife, Laura. ESRI would become in a few years the dominant force in the GIS marketplace and create ArcInfo and ArcView software. The first conference dealing with GIS took place in 1970 and was organized by Roger Tomlinson (key individual in the development of CGIS) and Duane Marble (professor at Northwestern University and early GIS innovator). Today, numerous conferences dealing with GIS run every year attracting thousands of attendants.

In the 1980s and 1990s, many GIS applications underwent substantial evolution regarding features and analysis power. Many of these packages were being refined by private companies who could see the future commercial potential of this software. Some of the popular commercial applications launched during this period include ArcInfo, ArcView, MapInfo, SPANS GIS, PAMAP GIS, INTERGRAPH, and SMALLWORLD. It was also during this period that many GIS applications moved from expensive minicomputer workstations to personal computer hardware.

There is a technology that exists that can bring together remote sensing data, GPS data points, spatial and non-spatial data, and spatial statistics into a single, dynamic system for analysis and that is a geographic information system (GIS). A GIS is a powerful database system that allows users to acquire, organize, store, and most importantly analyze information about the physical and cultural environments. A GIS views the world as overlaying physical or cultural layers, each with quantifiable data that can be analyzed. A single GIS map of a national forest could have layers such as elevation, deciduous trees, evergreens, soil type, soil erosion rates, rivers and tributaries, major and minor roads, forest health, burn areas, regrowth, restoration, animal species type, trails, and more. Each of these layers would contain a database of information specific to that layer.

GIS combines computer cartography with a database management system. GIS consists of three subsystems: (1) an input system that allows for the collection of data to be used and analyzed for some purpose; (2) computer hardware and software systems that store the data, allow for data management and analysis, and can be used to display data manipulations on a computer monitor; (3) an output system that generates hard copy maps, images, and other types of output.

Two basic types of data are typically entered into a GIS. The first type of data consists of real-world phenomena and features that have some form of spatial dimension. Usually, these data elements are depicted mathematically in the GIS as either points, lines, or polygons that are referenced geographically (or geocoded) to some type of coordinate system. This type data is entered into the GIS by devices like scanners, digitizers, GPS, air photos, and satellite imagery. The other type of data is sometimes referred to as an attribute. Attributes are pieces of data that are connected or related to the points, lines, or polygons mapped in the GIS. This attribute data can be analyzed to determine patterns of importance. Attribute data is entered directly into a database where it is associated with feature data.

Within the GIS database, a user can enter, analyze, and manipulate data that is associated with some spatial element in the real world. The cartographic software of the GIS enables one to display the geographic information at any scale or projection and as a variety of layers which can be turned on or off. Each layer would show some different aspect of a place on the Earth. These layers could show things like a road network, topography, vegetation cover, streams and water bodies, or the distribution of annual precipitation received.

Nearly every discipline, career path, or academic pursuit uses geographic information systems because of the vast amount of data and information about the physical and cultural world. Disciplines and career paths that use GIS include: conservation, ecology, disaster response and mitigation, business, marketing, engineering, sociology, demography, astronomy, transportation, health, criminal justice and law enforcement, travel and tourism, news media, and the list could endlessly go on.

Now, GIS primarily works from two different spatial models: raster and vector. Raster models in GIS are images much like a digital picture. Each image is broken down into a series of columns and rows of pixels, and each pixel is georeferenced to somewhere on Earth’s surface is represents a specific numeric value – usually a specific color or wavelength within the electromagnetic spectrum. Most remote sensing images come into a GIS as a raster layer.

The other type of GIS model is called a vector model. Vector-based GIS models are based on the concept of points that are again georeferenced (i.e., given an x-, y-, and possibly z- location) to somewhere specific on the ground. From points, lines can be created by connecting a series of points and areas can be created by closing loops of vector lines. For each of these vector layers, a database of information can be attributed to it. So for example, a vector line of rivers could have a database associated with it such as length, width, stream flow, government agencies responsible for it, and anything else the GIS user wants to be connected to it. What these vector models represent is also a matter of scale. For example, a city can be represented as a point or a polygon depending on how zoomed in you are to the location. A map of the world would show cities as points, whereas a map of a single county may show the city as a polygon with roads, populations, pipes, or grid systems within it.


Dreifus, C. Naomi Oreskes Imagines the Future History of Climate Change. The New York Times(2014).
Science literacy: concepts, contexts, and consequences. (National Academies Press (US), 2016).
Shermer, M. What Is Pseudoscience? Scientific American (2011).
Railsback, B. L. T. C. Chamberlin’s “Method of Multiple Working Hypotheses”: An encapsulation for modern students. Houston Geological Society Bulletin 47, 68–69 (2004).
Martin, C. Subverting Aristotle: Religion, History, and Philosophy in Early Modern Science. (Baltimore : Johns Hopkins University Press., 2014).
Marshall, J. A short history of Greek philosophy. (Andrews UK Limited, 2010).
Saliba, G. Islamic science and the making of the European renaissance. (MIT Press, 2007).
Hogendijk, J. P. & Sabra, A. I. The Enterprise of Science in Islam: New Perspectives. (MIT Press, 2003).
Beckwith, C. How western Europe developed a full scientific method. Berfrois (2013).
Goldstein, B. R. Copernicus and the origin of his heliocentric system. Journal for the History of Astronomy 33, 219–235 (2002).
Repcheck, J. Copernicus’ secret: How the scientific revolution began. (Simon and Schuster, 2007).
Kolbert, E. The sixth extinction: an unnatural history. (Henry Holt and Co., 2014).
Bocking, S. Nature’s experts: science, politics, and the environment. (Rutgers University Press, 2004).

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Chapter 3 Planet earth and Plate tectonics for print only


Earth is a terrestrial planet in the solar system, and it is very much like the other inner planets, at least in its size, shape, and composition. However, many features make Earth very different from the planets and any other planet that we know of so far.

Earth is a sphere or, more correctly, an oblate spheroid, which is a sphere that is a bit squished down at the poles and bulges a bit at the equator. Alternatively, to be more technical, the minor axis (the diameter through the poles) is smaller than the major axis (the diameter through the equator). When the earth is cut into equal halves, each half is called a hemisphere. North of the equator is the northern hemisphere and south of the equator is the southern hemisphere. Eastern and western hemispheres are also designated.

Even the ancient Greeks knew that Earth was round by observing the arc shape of the shadow on the Moon during a lunar eclipse. The Sun and the other planets of the solar system are also spherical. Larger satellites, those that have enough mass for their gravitational attraction to have made them round, are as well.

Earth has a magnetic field that behaves as if the planet had a gigantic bar magnet inside of it. Earth’s magnetic field also has a north and south pole and a magnetic field that surrounds it. The magnetic field arises from the convection of molten iron and nickel metal in Earth’s outer liquid iron core. Earth’s magnetic field extends several thousand kilometers into space. The magnetic field shields the planet from harmful radiation from the Sun.


3.1 Earth’s Rotation and revolution

Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis. Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earth’s rotation. At the same time that the Earth spins on its axis, it also orbits or revolves around the Sun, called a revolution.

A pendulum set in motion will not change its motion, and so the direction of its swinging should not change. However, Foucault observed that his pendulum did seem to change direction. Since he knew that the pendulum could not change its motion, he concluded that the Earth, underneath the pendulum was moving. An observer in space will see that Earth requires 23 hours, 56 minutes, and 4 seconds to make one complete rotation on its axis. However, because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is 24 hours. At the equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles, the movement speed is nearly nothing.

Description of relations between Axial tilt (or Obliquity), rotation axis, plane of orbit, celestial equator and ecliptic. Earth is shown as viewed from the Sun; the orbit direction is counter-clockwise (to the left).

For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year. The gravitational pull of the Sun keeps Earth and the other planets in orbit around the star. Like the other planets, Earth’s orbital path is an ellipse, so the planet is sometimes farther away from the Sun than at other times. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd, and the furthest is at aphelion (152 million km) on July 4th. Earth’s elliptical orbit has nothing to do with Earth’s seasons.

During one revolution around the Sun, Earth travels at an average distance of about 150 million km. Earth revolves around the Sun at an average speed of about 27 km (17 mi) per second, but the speed is not constant. The planet moves slower when it is at aphelion and faster when it is at perihelion.

The reason the Earth has seasons is that Earth is tilted 23.5 degrees on its axis. During the Northern Hemisphere summer the North Pole points toward the Sun, and in the Northern Hemisphere winter, the North Pole has tilted away from the Sun.

3.2 Geologic Time

In 1788, after many years of geological study, James Hutton, one of the early pioneers of geology, wrote the following about the age of the Earth: “The result, therefore, of our present inquiry is, that we find no vestige of a beginning, — no prospect of an end.” Although he was not precisely correct (there was a beginning, and there will be an end to planet Earth), he was trying to express the vastness of geological time that humans have a hard time perceiving. Although Hutton did not assign an age to the Earth, he was the first to suggest that the planet was very old. Today we know Earth is approximately 4.54 ± 0.05 billion years old, an age first calculated by Caltech professor Clair Patterson in 1956 by radiometrically dating meteorites with uranium-lead dating.

On a geologic scale, the lifespan of a human is very short, and we struggle to comprehend the depth of geologic time and slow geologic processes. Studying geologic time, also known as deep time, can help us overcome our limited view of Earth during our lifetime. For example, the science of earthquakes only goes back about 100 years; however, geologic evidence shows that large earthquakes have occurred in the past and will continue to occur in the future. Thus, human perspective of time does not always overlap with geologic timescales.


A diagram of the geological time scale.The largest division of time is the Eon—Hadean, Archean, Proterozoic (sometimes combined together as the Precambrian), and Phanerozoic. Although life appeared more than 3,800 million of years ago (Ma), during most of Earth history from 3,500 Ma to 542 Ma (88 percent of geologic time), life forms consisted mainly of simple single-celled organisms such as bacteria. Only in more recent geologic time have more biologically complex organisms appeared in the geologic record.

3.3. Structure of the Earth

The fundamental unifying principle of geology and the rock cycle is the Theory of Plate Tectonics. Plate tectonics describes how the layers of the Earth move relative to each other. Specifically, the outer layer divided into tectonic or lithospheric plates. As the tectonic plates float on a mobile layer beneath called the asthenosphere, they collide, slide past each other, and split apart. At these plate boundaries, significant landforms are created, and rocks comprising the tectonic plates move through the rock cycle.

The following is a summary of the Earth’s layers based on chemical composition (or the chemical makeup of the layers). Earth has three main geological layers based on chemical composition – crust, mantle, and core. The outermost layer is the crust and is composed of mostly silicon, oxygen, aluminum, iron, and magnesium. There are two types of crust, continental and oceanic crust. Continental crust.  is about 50 kilometers (30 miles) thick, represents most of the continents, and is composed of low-density igneous and sedimentary rocks. Oceanic crust is approximately 10 kilometers (6 miles) thick, makes up most of the ocean floor, and covers about 70 percent of the planet. Oceanic crust is high-density igneous basalt-type rocks. The moving tectonic plates are made of crust, and some of the next layers within the earth called the mantle. The crust and this portion of the upper mantle are rigid and called the lithosphere and comprise the tectonic plates.

A cross section illustrating the main types of plate boundaries.


The oldest continental rocks are billions of years old, so the continents have had a lot of time for things to happen to them. Constructive forces cause physical features on Earth’s surface known as landforms to grow. Crustal deformation – when crust compresses, pulls apart, or slides past other crust – results in hills, valleys, and other landforms. Mountains rise when continents collide, when one slab of ocean crust plunges beneath another or a slab of continental crust to create a chain of volcanoes. Sediments are deposited to form landforms, such as deltas.

Volcanic eruptions can also be destructive forces that blow landforms apart. The destructive forces of weathering and erosion modify landforms. Water, wind, ice, and gravity are important forces of erosion.

Oceanic Basins

The ocean basins are all younger than 180 million years. Although the ocean basins begin where the ocean meets the land, the continent extends downward to the seafloor, so the continental margin is made of continental crust.

The ocean floor itself is not totally flat. The most distinctive feature is the mountain range that runs through much of the ocean basin, known as the mid-ocean ridge. The deepest places of the ocean are the ocean trenches, many of which are located around the edge of the Pacific Ocean. Chains of volcanoes are also found in the center of the oceans, such as in the area of Hawaii. Flat plains are found on the ocean floor with their features covered by mud.

Map showing the underwater topography (bathymetry) of the ocean floor. Like land terrain, the ocean floor has ridges, valleys, plains and volcanoes.

The mantle is below the crust and is the most significant layer by volume, extending down to about 2,900 km (1,800 miles). The mantle is mostly solid and made of peridotite, a high-density rock composed of silica, iron, and magnesium. The upper part of this solid material is so hot that it is flexible and allows the tectonic plates floating on it to move relative to each other. Under the mantle is the 3,500 km (2,200 mi) thick core made of iron and nickel. The outer core is liquid, and the inner core is solid. Rotations within the solid and liquid metallic core generate Earth’s magnetic field.

Interior structure of Earth.

3.4 Rocks


A rock is a naturally formed, non-living earth material composed of one or more minerals or mineraloids (Typically, substances like coal, pearl, opal, or obsidian that do not fit the definition of a mineral are called mineraloids.). The mineral grains in a rock may be so tiny that they can only see them with a microscope, or several centimeters in size.

There are three main types of rocks composed of minerals: igneous (rocks crystallizing from molten material), sedimentary (rocks composed of products of mechanical weathering (sand, gravel, etc.) and chemical weathering (things precipitated from solution), and metamorphic (rocks produced by alteration of other rocks by heat and pressure. Click here to learn more about rocks and minerals from the Utah Geologic Survey.

What is a Mineral?

Minerals are categorized based on their chemical composition. Owing to similarities in composition, minerals within the same group may have similar characteristics. Geologists have a precise definition of minerals. A material is characterized as a mineral if it meets all of the following traits:


Crystalline Solid

Minerals are crystalline solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. The pattern of atoms in different samples of the same mineral is the same. Is glass a mineral? Without a crystalline structure, even natural glass is not a mineral.

Inorganic Substances

Organic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates, and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral? Coal is a classified as a sedimentary rock but is not a mineral.

Natural Processes

Minerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earth’s crust is a mineral. Is a diamond created in a laboratory by placing carbon under high pressures a mineral? No. Do not buy a laboratory-made “diamond” for jewelry without realizing it is not technically a mineral. But also be careful you do not purchase blood diamonds or other minerals that were mined to fund war, mass murders, or genocides.

Chemical Composition

Nearly all (98.5 percent) of Earth’s crust is made up of only eight elements – oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium – and these are the elements that make up most minerals.

All minerals have a specific chemical composition. The mineral silver is made up of only silver atoms and diamond is made only of carbon atoms, but most minerals are made up of chemical compounds. Each mineral has its own chemical formula. Halite is NaCl (sodium chloride). Quartz is always made of two oxygen atoms bonded to a silicon atom, SiO2. If a mineral contains any other elements in its crystal structure, it is not quartz.

A hard mineral containing covalently bonded carbon is diamond, but a softer mineral that also contains calcium and oxygen along with carbon is calcite. Some minerals have a range of chemical composition. Olivine always has silicon and oxygen as well as iron or magnesium or both.

Finding and Mining Minerals

Geologic processes create and concentrate minerals that are valuable natural resources. Geologists study geological formations and then test the physical and chemical properties of soil and rocks to locate possible ores and determine their size and concentration. A mineral deposit will only be mined if it is profitable. A concentration of minerals is only called an ore deposit if it is profitable to mine. There are many ways to mine ores.

Surface mining allows extraction of ores that are close to Earth’s surface. Overlying rock is blasted, and the rock that contains the valuable minerals is placed in a truck and taken to a refinery. Surface mining includes open-pit mining and mountaintop removal. Other methods of surface mining include strip mining, placer mining, and dredging. Strip mining is like open pit mining but with material removed along a strip.

Placers are valuable minerals found in stream gravels. California’s nickname, the Golden State, can be traced back to the discovery of placer deposits of gold in 1848. The gold weathered out of hard metamorphic rock in the western Sierra Nevada, which also contains deposits of copper, lead, zinc, silver, chromite, and other valuable minerals. The gold traveled down rivers and then settled in gravel deposits. Currently, California has active mines for gold and silver and for non-metal minerals such as sand and gravel, which are used for construction.

Kennecott Copper Mine in Salt Lake City, Utah.

Underground mining is used to recover ores that are deeper into Earth’s surface. Miners blast and tunnel into rock to gain access to the ores. How underground mining is approached – from above, below, or sideways – depends on the placement of the ore body, its depth, concentration of ore, and the strength of the surrounding rock. Underground mining is costly and dangerous. Fresh air and lights must also be brought into the tunnels for the miners, and accidents are far too frequent.

The ore’s journey to becoming a useable material is only just beginning when the ore leaves the mine. Rocks are crushed so that the valuable minerals can be separated from the waste rock. Then the minerals are separated out of the ore. To extract the metal from the ore, the rock is melted at a temperature greater than 900°C, which requires much energy. Extracting metal from rock is so energy intensive that if you recycle just 40 aluminum cans, you will save the energy equivalent of one gallon of gasoline.

Although mining provides people with many necessary resources, the environmental costs can be high. Surface mining clears the landscape of trees and soil, and nearby streams and lakes are inundated with sediment. Pollutants from the mined rock, such as heavy metals, enter the sediment and water system. Acids flow from some mine sites, changing the composition of nearby waterways.
U.S. law has changed so that in recent decades a mine region must be restored to its natural state, a process called reclamation. This is not true of older mines. Pits may be refilled or reshaped and vegetation planted. Pits may be allowed to fill with water and become lakes or may be turned into landfills. Underground mines may be sealed off or left open as homes for bats.

Some minerals are valuable because they are beautiful. Jade has been used for thousands of years in China. Diamonds sparkle on many engagement rings. Minerals like jade, turquoise, diamonds, and emeralds are gemstones. A gemstone, or gem, is a material that is cut and polished for jewelry. Gemstones are usually rare and do not break or scratch easily. Most are cut along cleavage faces and then polished so that light bounces back off the cleavage planes. Light does not pass through gemstones that are opaque, such as turquoise. Gemstones are not just used in jewelry. Diamonds are used to cut and polish other materials, such as glass and metals, because they are so hard. The mineral corundum, of which ruby and sapphire are varieties, is used in products such as sandpaper.

Minerals are used in much less obvious places. The mineral gypsum is used for the sheetrock in homes. Window glass is made from sand, which is mostly quartz. Halite is mined for rock salt. Copper is used in electrical wiring, and bauxite is the source for the aluminum used in soda cans.

3.5 The Rock Cycle

The most fundamental view of Earth materials is the rock cycle, which presents the primary materials that comprise the Earth and describes the processes by which they form and relate to each other. The rock cycle is usually said to begin with a hot molten liquid rock called magma or lava. Magma forms under the Earth’s surface in the crust or mantle and erupts on Earth’s surface as lava. When magma or lava cools, it solidifies by a process called crystallization in which minerals grow within the magma or lava. The rock that results from this is an igneous rock from the Latin word ignis, meaning “fire.”

Igneous rocks, as well as other types of rocks, on Earth’s surface, are exposed to processes of weathering and erosion to produce sediments. Weathering is the physical and chemical breakdown of rocks into smaller fragments and erosion is the removal of those fragments from their original location. Once igneous rocks are broken down and transported, these fragments or grains are considered sediments. Sediments such as gravel, sand, silt, and clay can be transported by water in the form of streams, ice in the form of glaciers, and air in the form of wind.  Sediments ultimately come to rest in a process known as deposition. The deposited sediments accumulate in place, often under water such as a shallow marine environment, get buried.

Within the burial process, the sediments go through compaction by the weight of overlying sediments and cementation as minerals in groundwater glue the sediments together. The process of compacting and cementing sediments together is lithification, and lithified sediments are considered a sedimentary rock, such as sandstone and shale. Other sedimentary rocks, known as chemical sedimentary rocks, are not made of weathered and eroded sedimentary fragments. They are instead made by direct chemical precipitation of minerals.

Pre-existing rocks may be metamorphosed into a metamorphic rock, meta- means “change”, -morphos means “form” or “shape.” When rocks are subjected to extreme increases in temperatures or pressures, the minerals alter into enlarged crystals, or entirely new minerals with similar chemical make up. These high temperatures and pressures can occur when rocks are buried deep within the Earth’s crust or where they come into contact with hot magma or lava. In some cases, the temperature and pressure conditions can allow rocks to melt and create magma and lava, thus showing the cyclical nature of the rock cycle as new rocks are born.

Click here to learn more about various types of igneous, sedimentary, and metamorphic rocks from the Utah Geologic Survey (UGS).


3.6 Igneous Rocks

Igneous rocks form from the cooling and hardening of molten magma in many different environments. These rocks are identified by their composition and texture. More than 700 different types of igneous rocks are known.

Russia’s Sarychev Volcano, on Matua Island in the Kuril Islands, erupting on 12 June 2009, as seen from the International Space Station (ISS).

Magma Composition

The rock beneath the Earth’s surface is sometimes heated to high enough temperatures that it melts to create magma. Different magmas have different composition and contain whatever elements were in the rock that melted. Magmas also contain gases. The main elements are the same as the elements found in the crust. Whether rock melts to create magma depends on:

As a rock heats up, the minerals that melt at the lowest temperatures will melt first. Partial melting occurs when the temperature on a rock is high enough to melt only some of the minerals in the rock. The minerals that will melt will be those that melt at lower temperatures. Fractional crystallization is the opposite of partial melting. This process describes the crystallization of different minerals as magma cools.

If the liquid separates from the solids at any time in partial melting or fractional crystallization, the chemical composition of the liquid and solid will be different. When that liquid crystallizes, the resulting igneous rock will have a different composition from the parent rock.

Intrusive Igneous Rock

Igneous rocks are called intrusive when they cool and solidify beneath the surface. When magma cools within the Earth, the cooling proceeds slowly. Intrusive igneous rocks cool slower than extrusive igneous rocks, which allows for larger crystal structure to take develop.

Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought igneous rocks to the surface. Yosemite is a classic example of intrusive igneous rock. The molten magma never reached Earth’s surface, so the molten material had millions of years to cool down slowly to form granite. Later, geologic forces and erosion have caused those granite plutons to surface as they are today.

Extrusive Igneous Rock

Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks. Extrusive igneous rocks cool much more rapidly than intrusive rocks, reducing the time for crystal structure to form within the rocks.

Cooling rate and gas content create a variety of rock textures. Lavas that cool exceptionally rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture.

Human Uses of Igneous Rock

Igneous rocks have a wide variety of uses. One significant use is as stone for buildings and statues. Granite is used for both of these purposes and is popular for kitchen countertops. Pumice is commonly used as an abrasive as household products or for smoothing skin. Ground up pumice stone is sometimes added to toothpaste to act as an abrasive material to scrub teeth. Peridotite is sometimes mined for peridot, a type of olivine that is used in jewelry. Diorite was used extensively by ancient civilizations for vases and other decorative artwork and is still used for art today.

3.7 Sedimentary Rock

Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types. Sediments may include:

Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break rock into smaller pieces. Physical weathering breaks the rocks apart, whereas chemical weathering dissolves the less stable minerals. These original elements of the minerals end up in solution, and new minerals may form. Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion.

Streams carry vast amounts of sediment. The more energy the water has, the larger the particle it can carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles.

Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and swamps. Avalanches drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited. Red rocks form where oxygen is present, whereas darker sediments form when the environment is oxygen-poor.

Sedimentary Rock Formation

Accumulated sediments harden into rock by a process called lithification. Two important steps are needed for sediments to lithify.
Sediments are squeezed together by the weight of overlying sediments on top of them, called compaction. Cemented, non-organic sediments become clastic rocks. If organic material is included, they are bioclastic rocks.

Fluids fill in the spaces between the loose particles of sediment and crystallize to create a rock by cementation. When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks.

Biochemical sedimentary rocks form in the ocean or a salt lake. Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue. When the organism dies, it sinks to the ocean floor to become biochemical sediment, which may then become compacted and cemented into solid rock.

Delicate Arch, in Moab, Utah.

Human Use of Sedimentary Rock

Sedimentary rocks are used as building stones, although they are not as hard as igneous or metamorphic rocks. Sedimentary rocks are used in construction. Sand and gravel are used to make concrete; they are also used in asphalt. Many economically valuable resources come from sedimentary rocks. Iron ore and aluminum are two examples.

3.8 Metamorphic Rock

Metamorphism is the addition of heat and/or pressure to existing rocks, which causes them to change physically and/or chemically so that they become a new rock. Metamorphic rocks may change so much that they may not resemble the original rock.

Any type of rock – igneous, sedimentary, or metamorphic – can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the existing rock’s physical or chemical makeup without melting the rock entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of the different chemical composition. Hornfels, with its alternating bands of dark and light crystals, is an excellent example of how minerals rearrange themselves during metamorphism.

Extreme pressure may also lead to foliation, the flat layers that form in rocks as pressure squeezes the rocks. Foliation forms typically when pressure is exerted in only one direction. Metamorphic rocks may also be non-foliated. Quartzite and limestone are nonfoliated. The two main types of metamorphism are both related to heat within Earth:

Quartzite is very hard and is often crushed and used in building railroad tracks. Schist and slate are sometimes used as building and landscape materials. Graphite, the “lead” in pencils, is a mineral commonly found in metamorphic rocks.

The Utah Geologic Survey has several resources related to landforms in Utah. They have also created a fun story map called GeoSights of popular geologic sights within the State of Utah.

Plate tectonics

Revolution is a word usually reserved for significant political or social changes. In science, there have been several revolutions of ideas (paradigm shifts) that have forced scientists to re-examine their entire field. Darwin’s On the Origin of Species in 1859, Mendel’s discovery of genetics in 1866, and the discovery of DNA by James Watson, Francis Crick, and Rosalind Franklin in the 1950s did that for biology. Albert Einstein’s relativity and quantum mechanics concepts in the early twentieth century did the same for Newtonian physics. Plate tectonics was just as revolutionary for geology. Plate tectonics, the idea that the outer part of the Earth moves and causes earthquakes, mountains, and volcanoes, is the lens through which geologic study must be viewed because all earth processes make more sense in this context. Its importance in understanding how the world works is why it is the first topic of discussion in this text.

3.9 Continental Drift Hypothesis

Alfred Wegener (1880-1930) was a German scientist who specialized in meteorology and climatology. He had a knack for questioning accepted ideas, and this started in 1910 when he disagreed with isostasy (vertical land movement due to the weight being removed or added) as the explanation for the Bering Land Bridge. After literary reviews, he published a hypothesis stating the continents had moved in the past. While he did not have the precise mechanism worked out, he had a long list of evidence that backed up his hypothesis of continental drift.

Early Evidence for Continental Drift

The first piece of evidence is that the shape of the coastlines of some continents fit together like pieces of a jigsaw puzzle. Since the first world map, people have noticed the similarities in the coastlines of South America and Africa, and the continents being ripped apart had even been mentioned as an explanation. Antonio Snider-Pellegrini even did preliminary work on continental separation and matching fossils in 1858.

What Wegener did differently than others was synthesized a significant amount of data in one place, as well as use the shape of the continental shelf, the actual edge of the continent, instead of the current coastline, which fit even better than previous efforts. Wegener also compiled and added to evidence of similar rocks, fossils, and glacial formations across the oceans.

Location of countries if Pangea existed today.

Fossil Evidence

For example, the primitive aquatic reptile Mesosaurus was found on the separate coastlines of the continents of Africa and South America, and the reptile Lystrosaurus was found on Africa, India, and Antarctica. These were land-dwelling creatures that could not have swam across an entire ocean; thus this was explained away by opponents of continental drift by land bridges. The land bridges, which, in the hypothesis of proponents, had eroded away, allowed animals and plants to move between the continents. However, some of the presumed land bridges would have had to have stretched across broad, deep oceans.

Geologic Evidence

Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway. Wegener concluded that they formed a single mountain range that was separated as the continents drifted.

Climatic Evidence

Another significant piece of evidence was climate anomalies. Late Paleozoic glacial evidence was found in widespread, warm areas like southern Africa, India, Australia, and the Arabian subcontinent. Wegener himself had found evidence of tropical plant fossils in areas north of the Arctic Circle. According to Wegener, the simpler explanation that fit all the climate, rock, and fossil observations, mainly as more data were collected, involved moving continents.

Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on.

Continental drift fossil evidence. As noted by Snider-Pellegrini and Alfred Wegener, the locations of certain fossil plants and animals on present-day, widely separated continents would form definite patterns (shown by the bands of colors), if the continents are rejoined.

Proposed Mechanism for Continental Drift

Wegener’s work was considered a fringe theory for his entire life. One of the most significant apparent flaws and easiest dismissals of Wegener’s hypothesis was a mechanism for movement of the continents. The continents did not appear to move, and extraordinary evidence would need to be provided to change the minds of the establishment, including a mechanism for movement. Other pro-continental drift followers had used expansion, contraction, or even the origin of the Moon as ideas to how the continents moved. Wegener used centrifugal forces and precession to explain the movement, but that was proven wrong. He had some speculation about seafloor spreading, with hints of convection within the earth, but these were unsubstantiated. As it turns out, convection within the mantle has been revealed as a significant force in driving plate movements, according to current knowledge.

3.10 Development of the Theory of Plate Tectonics

Wegener died in 1930 on an expedition in Greenland. In his lifetime, he was poorly respected, and his ideas of moving continents seemed destined to be lost to history as a fringe idea. However, starting in the 1950s, evidence started to trickle in that made continental drift more viable. By the 1960’s, there was enough evidence supporting Wegener’s missing mechanism, seafloor spreading, allowing the hypothesis of continental drift to develop into the Theory of Plate Tectonics. Widespread acceptance among scientists has transformed Wegener’s hypothesis to a Theory. Today, GPS and earthquake data continue to back up the theory. Below are the pieces of evidence that allowed the transformation.

The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which float on the fluid-like (visco-elastic solid) asthenosphere. The relative fluidity of the asthenosphere allows the tectonic plates to undergo motion in different directions. This map shows 15 of the largest plates.

Mapping the Ocean Floors

Starting in 1947 and using an adaptation of SONAR, researchers began to map a poorly-understood topographic, and thermal high in the mid-Atlantic . Bruce Heezen and Marie Tharp were the first to make a detailed map of the ocean floor, and this map revealed the mid-Atlantic Ridge, a basaltic feature, unlike the continents. Initially, this was thought to be part of an expanding Earth or a mechanism for the growth of the ocean. Transform faults were also added to explain movements more completely. When it was later realized that earthquake epicenters were also located within this feature, the idea that this was part of continental movement took hold.

Another way the seafloor was mapped was magnetically. Scientists had long known of strange magnetic anomalies (magnetic values that differ from expected values) associated with the ocean floor. This tool was adapted by geologists later for further study of the ocean depths, including strange alternating symmetrical stripes on both sides of a feature (which would be discovered later as the mid-ocean ridge) showing reversing magnetic pole directions. By 1963, these magnetic stripes would be explained in concordance with the spreading model of Hess and others.

Seafloor sediment was also an important feature that was measured in the oceans, both with dredging and with drilling. Sediment was believed to have been piling up on ocean floors for a very long time in a static model of accumulation. Initial studies showed less sediment than expected, and initial results were even used to argue against continental movement. With more time, researchers discovered thinner sediment close to ridges, indicating a younger age.

As the video below explains, today scientists are also able to use satellite imagery to map the ocean floor.

Seafloor Spreading Hypothesis

World War II gave scientists the tools to find the mechanism for continental drift that had eluded Wegener. Maps and other data gathered during the war allowed scientists to develop the seafloor spreading hypothesis. This hypothesis traces oceanic crust from its origin at a mid-ocean ridge to its destruction at a deep sea trench and is the mechanism for continental drift.

During World War II, battleships and submarines carried echo sounders to locate enemy submarines. Echo sounders produce sound waves that travel outward in all directions, bounce off the nearest object, and then return to the ship. By knowing the speed of sound in seawater, scientists calculate the distance to the object based on the time it takes for the wave to make a round-trip. During the war, most of the sound waves ricocheted off the ocean bottom. This animation shows how sound waves are used to create pictures of the seafloor and ocean crust.

After the war, scientists pieced together the ocean depths to produce bathymetric maps, which reveal the features of the ocean floor as if the water were taken away. Even scientists were amazed that the seafloor was not completely flat. What was discovered was a large chain of mountains along the deep seafloor, called mid-ocean ridges. Scientists also discovered deep-sea trenches along the edges of continents or in the sea near chains of active volcanoes. Finally, large, flat areas called abyssal plains we found. When they first observed these bathymetric maps, scientists wondered what had formed these features.

Scientists brought these observations together in the early 1960s to create the seafloor spreading hypothesis. In this hypothesis, hot buoyant mantle rises up a mid-ocean ridge, causing the ridge to rise upward. The hot magma at the ridge erupts as lava that forms new seafloor. When the lava cools, the magnetite crystals take on the current magnetic polarity and as more lava erupts, it pushes the seafloor horizontally away from ridge axis.

The magnetic stripes continue across the seafloor. As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the continent away from the ridge axis. If the oceanic crust reaches a deep sea trench, it sinks into the trench and is lost into the mantle. Scientists now know that the oldest crust is coldest and lies deepest in the ocean because it is less buoyant than the hot new crust.

Seafloor spreading and subduction.

The Unifying Theory of Plate Tectonics

Using all of the evidence mentioned, the theory of plate tectonics took shape. In 1966, J. Tuzo Wilson was the first scientist to put the entire picture together of an opening and closing ocean. Before long, models were proposed showing the plates moving concerning each other with clear boundaries between them, and scientists had also started to piece together complicated tectonic histories. The plate tectonic revolution had taken hold.

Seafloor and continents move around on Earth’s surface, but what is actually moving? What portion of the Earth makes up the “plates” in plate tectonics? This question was also answered because of technology developed during the Cold War. The tectonic plates are made up of the lithosphere. During the 1950s and early 1960s, scientists set up seismograph networks to see if enemy nations were testing atomic bombs. These seismographs also recorded all of the earthquakes around the planet. The seismic records could be used to locate an earthquake’s epicenter, the point on Earth’s surface directly above the place where the earthquake occurs. Earthquake epicenters outline these tectonic plates. Mid-ocean ridges, trenches, and large faults mark the edges of these plates along with where earthquakes occur.

The lithosphere is divided into a dozen major and several minor tectonic plates. The plates’ edges can be drawn by connecting the dots that mark earthquakes’ epicenters. A single plate can be made of all oceanic lithosphere or all continental lithosphere, but nearly all plates are made of a combination of both. Movement of the plates over Earth’s surface is termed plate tectonics. Plates move at a rate of a few centimeters a year, about the same rate fingernails grow.

3.11 Layers of the Earth

To understand the details of plate tectonics, one must first understand the layers of the Earth. Humankind has insufficient first-hand information regarding what is below; most of what we know is pieced together from models, seismic waves, and assumptions based on meteorite material. In general, the Earth can be divided into layers based on chemical composition and physical characteristics.

Chemical Layers

The Earth has three main divisions based on their chemical composition, which means chemical makeup. Indeed, there are countless variations in composition throughout the Earth, but it appears that only two significant changes take place, leading to three distinct chemical layers.

Internal structure of the earth.


The outermost chemical layer and the layer humans currently reside on is known as the crust. The crust has two types: continental crust, which is relatively low density and has a composition similar to granite, and oceanic crust, which is relatively high density (especially when it is cold and old) and has a composition similar to basalt. In the lower part of the crust, rocks start to be more ductile and less brittle, because of added heat. Earthquakes, therefore, generally occur in the upper crust.

At the base of the crust is a substantial change in seismic velocity called the Mohorovičić Discontinuity, or Moho for short, discovered by Andrija Mohorovičić (pronounced mo-ho-ro-vee-cheech) in 1909 by studying earthquake wave paths in his native Croatia. It is caused by the dramatic change in composition that occurs between the mantle and the crust. Underneath the oceans, the Moho is about 5 km down. Under continents, the average is about 30-40 km, except near a sizeable mountain-building event, known as an orogeny, where that thickness is about doubled.


The mantle is the layer below the crust and above the core, and is the most substantial layer by volume, extending from the base of the crust to a depth of about 2900 km. Most of what we know about the mantle comes from seismic waves, though some direct information can be gathered from parts of the ocean floor that are brought to the surface, known as ophiolites. Also, carried within magma are xenoliths, which are small chunks of lower rock carried to the surface by eruptions. These xenoliths are mainly made of the rock peridotite, which on the scale of igneous rocks is ultramafic. We assume the majority of the mantle is made of peridotite.


The core of the Earth, which has both liquid and solid components, is made mostly of iron and nickel and possibly minor oxygen. First discovered in 1906 by looking into seismic data, it took the union of modeling, astronomical insight, and seismic data to arrive at the idea that the core is mostly metallic iron. Meteorites contain much more iron than typical surface rocks, and if meteoric material is what made the Earth, the core would have formed as dense material (including iron and nickel) sank to the center of the Earth via its weight as the planet formed, heating the Earth intensely.

Physical Layers

The Earth can also be broken down into five distinct physical layers based on how each layer responds to stress. While there is some overlap in the chemical and physical designations of layers, specifically the core-mantle boundary, there are significant differences between the two systems.

Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches


The lithosphere, with ‘litho’ meaning rock, is the outermost physical layer of the Earth. Including the crust, it has both an oceanic component and a continental component. Oceanic lithosphere, ranging from a thickness of zero (at the forming of new plates on the mid-ocean ridge) to 140 km, is thin and relatively rigid. Continental lithosphere is considerably more plastic in nature (especially with depth) and is overall thicker, from 40 to 280 km thick. Most importantly, the lithosphere is not continuous. It is broken into several segments that geologists call plates. A plate boundary is where two plates meet and move relative to each other. It is at and near plate boundaries where the real action of plate tectonics is seen, including mountain building, earthquakes, and volcanism.


The asthenosphere, with ‘astheno’ meaning weak, is the layer below the lithosphere. The most distinctive property of the asthenosphere is movement. While still solid, over geologic time scales it will flow and move because it is mechanically weak. It is in this layer that movement, partly driven by convection of intense interior heat, allows the lithospheric plates to move. Since certain types of seismic waves pass through the asthenosphere, we know that it is solid, at least at the very short time scales of the passage of seismic waves. The depth and occurrence of the asthenosphere are dependent on heat and can be very shallow at mid-ocean ridges and very deep in plate interiors and beneath mountains.


The mesosphere, or lower mantle as it is sometimes called, is more rigid and immobile than the asthenosphere, though still hot. This can be attributed to increased pressure with depth. Between approximately 410 and 660 km depth, the mantle is in a state of transition as minerals with the same composition are changed to various forms, dictated by the conditions of increasing pressure. Changes in seismic velocity show this, and this zone also can be a physical barrier to movement. Below this zone, the mantle is relatively uniform and homogeneous, as no major changes occur until the core is reached.

The outer core is the only liquid layer found within Earth. It starts at 2,890 km (1,795 mi) depth and extends to 5,150 km (3,200 mi). Inge Lehmann, a Danish geophysicist, in 1936, was the first to prove that there was an inner core that was solid within the liquid outer core based on analyzing seismic data. The solid inner core is about 1,220 km (758 mi) thick, and the outer core is about 2,300 km (1,429 mi) thick.

It seems like a contradiction that the hottest part of the Earth is solid, as high temperatures usually lead to melting or boiling. The solid inner core can be explained by understanding that the immense pressure inhibits melting, though as the Earth cools by heat flowing outward, the inner core grows slightly larger over time. As the liquid iron and nickel in the outer core moves and convects, it becomes the most likely source for Earth’s magnetic field. This is critically important to maintaining the atmosphere and conditions on Earth that make it favorable to life. Loss of outer core convection and the Earth’s magnetic field could strip the atmosphere of most of the gases essential to life and dry out the planet; much like what has happened to Mars.

3.12 Plate Tectonic Boundaries

Places, where oceanic and continental lithospheric tectonic plates meet and move relative to each other, are called active margins (e.g., the western coasts of North and South America). A location where continental lithosphere transitions into oceanic lithosphere without movement is known as a passive margin (e.g., the eastern coasts of North and South America). This is why tectonic plates may be made of both oceanic and continental lithosphere. In the process of plate tectonics, the lithospheric plates movement is the primary force that causes the majority of features and activity on the Earth’s surface that can be attributed to plate tectonics. This movement occurs (at least partially) via the drag of motion within the asthenosphere and because of density.

As they move, the tectonic plates interact with each other at the boundaries between the tectonic plates. These interactions are the primary drivers of mountain building, earthquakes, and volcanism on the planet. In a simplified plate tectonic model, plate interaction can be placed in one of three categories. In places where plates move toward each other, the boundary is known as convergent. In places where plates move apart, the boundary is known as divergent. In places where the plates slide past each other, the boundary is known as a transform boundary. The next three subchapters will explain the details of the movement at each type of boundary.

Tectonic plate boundaries and seafloor spreading.

Convergent Boundaries

Convergent boundaries, sometimes called destructive boundaries, are places where two or more tectonic plates have a net movement toward each other. The key to convergent boundaries is understanding the density of each plate involved in the movement. Continental lithosphere is always lower in density and is buoyant when compared to the asthenosphere. Oceanic lithosphere, on the other hand, is denser than continental lithosphere and, when old and cold, may even be denser than the asthenosphere. When plates of different density converge, the more dense plate sinks beneath, the less dense plate, a process called subduction.

Geologic provinces created by various orogenies.

Subduction is when oceanic lithosphere descends into the mantle due to its density. The average rate of subduction of oceanic crust worldwide is 25 miles per million years, about a half inch per year. Continental lithosphere can partially subduct if attached to sinking oceanic lithosphere, but its buoyancy does not allow it to subduct fully. As the tectonic plate descends, it also pulls the ocean floor down in a feature known as a trench. On average, the ocean floor is around 3-4 km deep. In trenches, the ocean can be more than twice as deep, with the Mariana Trench approaching a staggering 11 km.

When the subducting plate, known as a slab, submerges into the depths of the mantle, the heat and pressure are so immense that lighter materials, known as volatiles, like water and carbon dioxide are pushed out of the subducting plate into an area called the mantle wedge above. The volatiles are released mostly via hydrated minerals that revert to non-hydrated forms in these conditions. These volatiles, when mixed with asthenospheric material above the tectonic plate, lower the melting point of the material. At the temperature of that depth, the material melts to form magma. This process of magma generation is called flux melting. Magma, because of its lower density, migrates toward the surface, creating volcanism. This forms a curved chain of volcanoes, due to many boundaries being curved on a spherical Earth, a feature called an arc. The overriding plate which contains the arc can be either oceanic or continental, where some features are different, but the general architecture remains the same.

How subduction initiates is still a matter of some debate. Presumably, this would start at passive margins where oceanic and continental crust meet. At the current time, there is oceanic lithosphere that is denser than the underlying asthenosphere on either side of the Atlantic Ocean that is not currently subducting. Why has it not turned into an active margin? Firstly, there is strength in the connection between the dense oceanic lithosphere and the less dense continental lithosphere it is connected to, which needs to be overcome. Gravity could cause the denser oceanic plate to force itself down, or the plate can start to flow ductility at a low angle. There is evidence that new subduction is starting off the coast of Portugal. Large earthquakes, like the 1755 Lisbon Earthquake, may even have something to do with this process of creating a subduction zone, though it is not definitive. Transform boundaries that have brought areas of different densities together are also thought to start subduction possibly.

Besides volcanism, subduction zones are also known for the largest earthquakes in the world. In places, the entire subducting slab can become stuck, and when the energy has built up too high, the entire subduction zone can slide at once along a zone extending for hundreds of kilometers along the trench, creating enormous earthquakes and tsunamis. The earthquakes can not only be large, but they can be deep, outlining the subducting slab as it descends. Subduction zones are the only places on Earth with fault surfaces large enough to create magnitude nine earthquakes. Also, because the faulting occurs beneath seawater, subduction also can create giant tsunamis, such as the 2004 Indian Ocean Earthquake and the 2011 Tōhoku Earthquake in Japan.

Subduction, which is a convergent motion, can have varying degrees of convergence. In places that have a high rate of convergence, mostly due to young, buoyant oceanic crust subducting, the subduction zone can create faulting behind the arc area itself, known as back-arc faulting. This faulting can be tensional, or this area is subject to compressional forces. A modern example of this occurs in the two ‘spines’ of the Andes Mountains. In the west, the mountains are formed from the volcanic arc itself; in the east, thrust faults have pushed up another, non-volcanic mountain range still part of the Andes. This type of thrusting can typically occur in two styles: thin-skinned, which only faults surficial rocks, and thick-skinned, which thrusts deeper crustal rocks. Oceanic-Continental Subduction

Oceanic-continental subduction occurs when an oceanic plate dives below continental plates. This boundary has a trench and mantle wedge, but the volcanoes are expressed in a feature known as a volcanic arc. A volcanic arc is a chain of mountain volcanoes, with famous examples including the Cascades of the Pacific Northwest (map) and the Andes of South America (map).

Continental-oceanic convergent boundary.

Oceanic-Oceanic Subduction

Oceanic-oceanic subduction zones have two significant differences from boundaries that have continental lithosphere. Firstly, each plate in an ocean-ocean plate boundary is capable of subduction. Therefore, it is typical that the denser, older, and colder of the two plates is the one that subducts. Secondly, since both plates are oceanic, volcanism creates volcanic islands instead of continental volcanic mountain ranges. This chain of active volcanoes is known as an island arc. There are many examples of this on Earth, including the Aleutian Islands off of Alaska (map), the Lesser Antilles in the Caribbean (map), and several island arcs in the western Pacific.

Oceanic-oceanic convergent boundary.

Continental-Continental Convergence

In places where two continental plates converge toward each other, subduction is not possible. This occurs where an ocean basin closes, and a passive margin is attempted to be driven down with the subducting slab. Instead of subducting beneath the continent, the two masses of continental lithosphere slam into each other in a process known as a collision. Collision zones are known for tall mountains and frequent, massive earthquakes, with little to no volcanism. With subduction ceasing with the collision, there is not a process to create the magma for volcanism.

Continental plates are too low density to subduct, which is why the process of collision occurs instead of subduction. Unlike the dense subducting slabs that form from oceanic plates, any attempt to subduct continental plates is short lived. An occasional exception to this is obduction, in which a part of a continental plate is caught beneath an oceanic plate, formed in collision zones or with small plates caught in subduction zones. This imbalance in density is solved by the continental material buoying upward, bringing oceanic floor and mantle material to the surface, and is the primary source of ophiolites. An ophiolite consists of rocks of the ocean floor that are moved onto the continent, which can also expose parts of the mantle on the surface.

Continental-continental convergent boundary.

Foreland basins can also develop near the mountain belt, as the lithosphere is depressed due to the mass of the mountains themselves. While subduction mountain ranges can cause this, collisions have many examples, with possibly the best modern example being the Persian Gulf, a feature only there due to the weight of the nearby Zagros Mountains. Collisions are powered by the subducting oceanic lithosphere, and eventually stop as the continental plates combine into a larger mass. In truth, a small portion of the continental crust can be driven down into the subduction zone, though due to its buoyancy, it returns to the surface over time. Because of the relative plastic nature of continental lithosphere, the zone of deformation is much broader. Instead of earthquakes located along a narrow boundary, collision earthquakes can be found hundreds of miles from the suture between the land masses.

The best modern example of this process occurs concurrently in many locations across the Eurasian continent and includes mountain building in the Pyrenees (the Iberian Peninsula converging with France, map), Alps (Italy converging into central Europe, map), Zagros (Arabia converging into Iran, map), and Himalayan (India converging into Asia, map) ranges. Eventually, as ocean basins close, continents join together to form a massive accumulation of continents called a supercontinent, a process that has taken place in hundreds of million-year cycles over earth’s history.

Divergent Boundaries

Divergent boundaries, sometimes called constructive boundaries, are places where two or more plates have a net movement away from each other. They can occur within a continental plate or an oceanic plate, though the typical pattern is for divergence to begin within continental lithosphere in a process known as “rift to drift,” described below.

Continental Rifting

Because of the thickness of continental plates, heat flow from the interior is suppressed. The shielding that supercontinents provide is even stronger, eventually causing upwelling of hot mantle material. This material uplift weakens overlying continental crust, and as convection beneath naturally starts pulling the material away from the area, the area starts to be deformed by tensional stress forming a valley feature known as a rift valley. These features are bounded by normal faults and include tall shoulders called horsts, and deep basins called grabens. When rifts form, they can eventually cause linear lakes, linear seas, and even oceans to form as divergent forces continue.

Divergent boundary

This breakup via rifting, while initially seeming random, actually has two influences that dictate the shape and location of rifting. First of all, the stable interiors of some continents, called a craton, are seemingly too strong to be broken apart by rifting. Where cratons are not a factor, rifting typically occurs along the patterns of a truncated icosahedron, or “soccer ball” pattern. This is the geometric pattern of fractures that requires the least amount of energy when expanding a sphere equally in all directions. Taking into account the radius of the Earth, this includes ~110 km segments of deformation and volcanism which have 120 degree turns, forming something known as failed rift arms. Even if the motion stops, a minor basin can develop in this weak spot called an aulacogen, which can form long-lived basins well after tectonic processes stop. These are places where extension started but did not continue. One famous example is the Mississippi Valley Embayment, which forms a depression through which the upper end of the Mississippi River flows. In places where the rift arms do not fail, for example, the Afar Triangle, three divergent boundaries can develop near each other forming a triple junction.

The Great Rift Valley, in eastern Africa is an example of a narrow rift valley.

Rifts come in two types: narrow and broad. Narrow rifts contain concentrated stress or divergent action. The best active example is the East African Rift Zone, where the horn of Africa near Somalia is breaking away from mainland Africa (map). Lake Baikal in Russia is also an active rift (map). Broad rifts distribute the deformation over a wide area of many fault-bounded locations, like in the western United States in a region known as the Basin and Range (map). The Wasatch Fault, which created the Wasatch Range in Utah, marks the eastern edge of the Basin and Range (map).

The Great Basin is an example of a broad rift valley.

Earthquakes, of course, do occur at rifts, though not at the severity and frequency of some other boundaries. Volcanism is also frequent in the extended, faulted, and thin lithosphere found at rift zones due to decompressional melting and faults acting as conduits for the lava reaching the surface. Many relatively young volcanoes dot the Basin and Range, and very strange volcanoes occur in East Africa like Ol Doinyo Lengai in Tanzania, which erupts carbonatite lavas, relatively cold liquid carbonate.

Mid-Oceanic Ridges

As rifting and volcanic activity progress, the continental lithosphere becomes more mafic and thinner, with the eventual result transforming the plate under the rifting area into the oceanic lithosphere. This is the process that gives birth to a new ocean, much like the narrow Red Sea (map) emerged with the movement of Arabia away from Africa. As the oceanic lithosphere continues to diverge, a mid-ocean ridge is formed.

A mid-ocean ridge, also known as a spreading center, has many distinctive features (map). They are the only places on Earth where the new oceanic lithosphere is being created, via slow oozing volcanism. As the oceanic lithosphere spreads apart, rising asthenosphere melts due to decreasing pressure and fills in the void, making the new lithosphere and crust. These volcanoes produce more lava than all the other volcanoes on Earth combined, and yet are not usually listed on maps of volcanoes due to the vast majority of mid-ocean ridges being underwater. Only rare locations, such as Iceland, are the volcanism and divergent characteristics seen on land. Technically, these places are not mid-ocean ridges, because they are above the surface of the seafloor. The video below is drone imagery of the Icelandic Lava River.

Alfred Wegener even hypothesized this concept of mid-ocean ridges. Because the lithosphere is very hot at the ridge, it has a lower density. This lower density allows it to isostatically ‘float’ higher on the asthenosphere. As the lithosphere moves away from the ridge by continued spreading, the plate cools and starts to sink isostatically lower, creating the surrounding abyssal plains with lower topography. Age patterns also match this idea, with younger rocks near the ridge and older rocks away from the ridge. Sediment patterns also thin toward the ridge, since the steady accumulation of dust and biologic material takes time to accumulate.

Mid-ocean ridges also are home to some of the unique ecosystems ever discovered, found around hydrothermal vents that circulate ocean water through the shallow oceanic crust and send it back out rich with chemical compounds and heat. While it was known for some time that hot fluids could be found on the ocean floor, it was only in 1977 when a team of scientists using the Diving Support Vehicle Alvin discovered a thriving community of organisms, including tube worms bigger than people. This group of organisms is not at all dependent on the sun and photosynthesis but instead relies on chemical reactions with sulfur compounds and heat from within the Earth, a process known as chemosynthesis. Before this discovery, the thought in biology was that the sun was the ultimate source of energy in ecosystems; now we know this to be false. Not only that, some have suggested it is from this that life could have started on Earth, and it now has become a target for extraterrestrial life (e.g., Jupiter’s moon Europa).

Transform Boundaries

A transform boundary, sometimes called a strike-slip or conservative boundary, is a place where the motion is of the plates sliding past each other. They can move in either dextral fashion with the side opposite moving toward the right or a sinistral fashion with the side opposite moving toward the left. Most transform boundaries can be viewed as a single fault or as a series of faults. As stress builds on adjacent plates attempting to slide them past each other, eventually a fault occurs and releases stress with an earthquake. Transform faults have a shearing motion and are common in places where tectonic stresses are transferred. In general, transform boundaries are known for only earthquakes, with little to no mountain building and volcanism.

Transform boundary.

The majority of transform boundaries are associated with mid-ocean ridges. As spreading centers progress, these aseismic fracture zone transform faults accommodate different amounts of spreading due to Eulerian geometry that a sphere rotates faster in the middle (Equator) than at the top (Poles) than along the ridge. However, the more significant transform faults, in the eyes of humanity, are the places where the motion occurs within continental plates with a shearing motion. These transform faults produce frequent moderate to large earthquakes. Famous examples include California’s San Andreas Fault (map), both the Northern and Eastern Anatolian Faults in Turkey (map), the Altyn Tagh Fault in central Asia (map), and the Alpine Fault in New Zealand (map).

Aerial photo of San Andreas Fault looking northwest onto the Carrizo Plain with Soda Lake visible at the upper left.

3.13 Wilson Cycle

The Wilson Cycle, named for J. Tuzo Wilson who first described it in 1966, outlines the origin and subsequent breakup of supercontinents. This cycle has been operating for the last billion years with supercontinents Pangaea and Rodinia, and possibly billions of years before that. The driving force of this is two-fold. The more straightforward mechanism arises from the fact that continents hold the Earth’s internal heat much better than the ocean basins. When continents congregate together, they hold more heat in which more vigorous convection can occur, which can start the rifting process. Mantle plumes are inferred to be the legacy of this increased heat and may record the history of the start of rifting. The second mechanism for the Wilson Cycle involves the destruction of plates. While rifting eventually leads to drifting continents, a few unanswered questions emerge:

To be sure, these are all factors in plate movement and the Wilson Cycle. It does appear, in the current best hypothesis, that there is a more significant component of slab pull than ridge push. Plate tectonic models are beginning to detail the next supercontinent, called Pangea Proxima, that will form 250 million years.

3.14 Hotspots

While the Wilson Cycle can give a general overview of plate motions in the past, another process can give more precise, but mainly recent, plate movement. A hot spot (map) is an area of rising magma, causing a series of volcanic centers which form volcanic islands in the ocean or craters/mountains on land. There is not a plate tectonic process, like subduction or rifting, that causes this volcanic activity; it seems as if disconnected to plate tectonics processes. Also first postulated by J. Tuzo Wilson, in 1963, hot spots are places that have a continual source of magma with no earthquakes, besides those associated with volcanism. The classic idea is that hot spots do not move, though some evidence has been suggested that the hot spots do move as well. Even though hotspots and plate tectonics seem independent, there are some relationships between them, and they have two components: Firstly, there are several hot spots currently and several others in the past that are believed to have begun at the time of rifting. Secondly, as plate tectonics moves the plates around, the assumed stationary nature of hot spots creates a track of volcanism that can measure past plate movement. By using the age of the eruptions from hot spots and the direction of the chain of events, one can identify a specific rate and direction of movement of a plate over the time the hot spot was active.

A diagram showing the Hawaii hotspot and the inferred underlying mantle plume in cross-section.

Hot spots are still very mysterious in their exact mechanism of magma generation. The main camps on hotspot mechanics are opposed. Some claim deep sources of heat, from as deep as the core, bring heat up to the surface in a structure called a mantle plume. Some have argued that not all hot spots are sourced from deep within the planet, and are sourced from shallower parts of the mantle. Others have mentioned how difficult it has been to image these deep features. The idea of how hot spots start is also controversial. Usually, divergent boundaries are tabbed as the start, especially during supercontinent break up, though some question whether extensional or tectonic forces alone can explain the volcanism. Subducting slabs have also been named as a cause for hotspot volcanism. Even impacts of objects from space have been used to explain plumes. However they are formed, there are dozens found throughout the Earth. Famous examples include the Tahiti, Afar Triangle, Easter Island, Iceland, the Galapagos Islands, and Samoa. The United States has two of the largest and best-studied examples: Hawai’i and Yellowstone.

Hawaiian Hot Spot

The big island of Hawai’i (map) is the active end of the Hawaiian-Emperor seamount chain, which stretches across the Pacific for almost 6000 km. The evidence for this hot spot goes back at least 80 million years, and presumably, the hot spot was around before then, but rocks older than that in the Pacific Plate had already subducted. The most striking feature of the chain is a significant bend that occurs about halfway through the chain that occurred about 50 million years ago. The change in direction has been more often linked to a plate reconfiguration, but also to other things like plume migration. While it is often assumed that mantle plumes do not move, much like the plumes themselves, this idea is under dispute by some scientists.

Yellowstone Supervolcano

The Yellowstone Hot Spot (map) is formed from rising magma, much like Hawai’i. The big difference is Hawai’i sits on a thin oceanic plate, which makes the magma easily come to the surface. Yellowstone, however, is on a continental plate. The thickness of the plate causes the generally much more violent and less frequent eruptions that have carved a curved path in the western United States for over 15 million years (see figure). Some have speculated an even earlier start to the hotspot, tying it to the Columbia River flood basalts and even 70 million-year-old volcanism in Canada’s Yukon.

The most recent significant eruption formed the current caldera and the Lava Creek Tuff. This eruption threw into the atmosphere about 1000 cubic kilometers of magma erupted 631,000 years ago. Ash from the eruption has been found as far away as Mississippi. The next eruption, when it occurs, should be of similar size, causing a massive calamity to not only the western United States, but also the world. These so-called “supervolcanic” eruptions have the potential for volcanic winters lasting years. With so much gas and ash filling the atmosphere, sunlight is blocked and unable to reach Earth’s surface as well as usual, which could drastically alter global environments and send worldwide food production into a tailspin.

Chapter 4 Weathering and Erosion for print only



Weathering is what takes place when a body of rock is exposed to the “weather” — in other words, to the forces and conditions that exist at Earth’s surface. Except for volcanic rocks and some sedimentary rocks, most rocks are formed at some depth within the crust. There they experience relatively constant temperature, high pressure, no contact with the atmosphere, and little or no moving water. Once a rock is exposed at the surface, which is what happens when the overlying rock is eroded, conditions change dramatically. Temperatures vary widely, there is much less pressure, oxygen and other gases are plentiful, and in most climates, water is abundant.

Hoodoos at Bryce Canyon National Park, Utah. Image source: Luca Galuzzi.

Weathering includes two main processes that are entirely different. One is the mechanical breakdown of rock into smaller fragments, and the other is the chemical change of the minerals within the rock to forms that are stable in the surface environment. Mechanical weathering provides fresh surfaces for attack by chemical processes, and chemical weathering weakens the rock so that it is more susceptible to mechanical weathering. Together, these processes create two significant products, one being the sedimentary clasts and ions in solution that can eventually become sedimentary rock, and the other being the soil that is necessary for our existence on Earth.

4.1 Mechanical Weathering

Intrusive igneous rocks form at depths of several hundreds of meters to several tens of kilometers. Sediments are turned into sedimentary rocks only when other sediments bury them to depths more than several hundreds of meters. Most metamorphic rocks are formed at depths of kilometers to tens of kilometers. Weathering cannot even begin until these rocks are uplifted through various processes of mountain building — most of which are related to plate tectonics — and the overlying material has been eroded, and the rock is exposed as an outcrop.

The critical agents of mechanical weathering are:

When a mass of rock is exposed by weathering and removal of the overlying rock, there is a decrease in the confining pressure on the rock, and the rock expands. This unloading promotes cracking of the rock, known as exfoliation.

Granitic rock tends to exfoliate parallel to the exposed surface because the rock is typically homogenous, and it does not have predetermined planes along which it must fracture. Sedimentary and metamorphic rocks, on the other hand, tend to exfoliate along predetermined planes.

Frost wedging, also called ice wedging, is the process by which water seeps into cracks in a rock, expands on freezing, and thus enlarges the cracks. The effectiveness of frost wedging is related to the frequency of freezing and thawing. Frost wedging is most effective in mountainous climates. In warm areas where freezing is infrequent, in very cold areas where thawing is infrequent, or in arid areas, where there is little water to seep into cracks, the role of frost wedging is limited.

In many mountainous regions, the transition between freezing nighttime temperatures and thawing daytime temperatures is frequent — tens to hundreds of times a year. Even in warm coastal areas, freezing and thawing transitions are common at higher elevations. A common feature in areas of active frost wedging is a talus slope — a fan-shaped deposit of fragments removed by frost wedging from the steep rocky slopes above.

Talus cones on the north shore of Isfjorden, Svalbard, Norway. Image source: Mark A. Wilson.

A related process, frost heaving, takes place within unconsolidated materials on gentle slopes. In this case, water in the soil freezes and expands, pushing the overlying material up. Frost heaving is responsible for winter damage to roads all over North America.

When saltwater seeps into rocks and then evaporates on a hot sunny day, salt crystals grow within cracks and pores in the rock. The growth of these crystals exerts pressure on the rock and can push grains apart, causing the rock to weaken and break. Salt weathering can also occur away from the coast because most environments have some salt in them.

The effects of plants and animals are significant in mechanical weathering. Roots can force their way into even the tiniest cracks, and then they exert tremendous pressure on the rocks as they grow, widening the cracks and breaking the rock. Although animals do generally not burrow through solid rock, they can excavate and remove huge volumes of soil, and thus expose the rock to weathering by other mechanisms.

Mechanical weathering is greatly facilitated by erosion, which is the removal of weathering products, allowing for the exposure of more rock for weathering. On the steep rock faces at the top of the cliff, rock fragments have been broken off by ice wedging, and then removed by gravity. This is a form of mass wasting. Other essential agents of erosion that also have the effect of removing the products of weathering include water in streams, ice in glaciers, and waves on the coasts.

4.2 Chemical Weathering

Chemical weathering results from chemical changes to minerals that become unstable when they are exposed to surface conditions. The kinds of changes that take place are highly specific to the mineral and the environmental conditions. Some minerals, like quartz, are virtually unaffected by chemical weathering, while others, like feldspar, are easily altered. In general, the degree of chemical weathering is most significant in warm and wet climates and least in cold and dry climates. The important characteristics of surface conditions that lead to chemical weathering are the presence of water (in the air and on the ground surface), the abundance of oxygen, and the presence of carbon dioxide, which produces weak carbonic acid when combined with water.

The Products of Weathering and Erosion

The products of weathering and erosion are the unconsolidated materials that we find around us on slopes, beneath glaciers, in stream valleys, on beaches, and in deserts. The nature of these materials — their composition, size, the degree of sorting, and degree of rounding — is determined by the type of rock that is being weathered, the nature of the weathering, the erosion, and transportation processes, and the climate.

The produces created from weathering range widely in size and shape depending on the processes involved. If and when deposits like these are turned into sedimentary rocks, the textures of those rocks will vary significantly. Importantly, when we describe sedimentary rocks that formed millions of years in the past, we can use those properties to make inferences about the conditions that existed during their formation.

4.3 Weathering and the Formation of Soil

Weathering is a key part of the process of soil formation, and soil is critical to our existence on Earth. Many people refer to any loose material on Earth’s surface as soil, but to geologists (and geology students) soil is the material that includes organic matter, lies within the top few tens of centimeters of the surface, and is vital in sustaining plant growth.

Soil is a complex mixture of minerals (approximately 45 percent), organic matter (approximately 5 percent), and empty space (approximately 50 percent, filled to varying degrees with air and water). The mineral content of soils is variable, but is dominated by clay minerals and quartz, along with minor amounts of feldspar and small fragments of rock. The types of weathering that take place within a region have a significant influence on soil composition and texture. For example, in a warm climate, where chemical weathering dominates, soils tend to be more abundant in clay. Soil scientists describe soil texture in terms of the relative proportions of sand, silt, and clay. The sand and silt components in this diagram are dominated by quartz, with lesser amounts of feldspar and rock fragments, while the clay component is dominated by the clay minerals.

A natural compound called tunicamycin, which is found in certain soil types, could bolster penicillin’s effectiveness against antibiotic-resistant germs. Image by the U.S. Department of Agriculture.

Soil forms through accumulation and decay of organic matter and the mechanical and chemical weathering processes described above. The factors that affect the nature of soil and the rate of its formation include climate (especially average temperature and precipitation amounts, and the following types of vegetation), the type of parent material, the slope of the surface, and the amount of time available.

Water erosion is accentuated on sloped surfaces because fast-flowing water has greater eroding power than still water. Raindrops can disaggregate exposed soil particles, putting the finer material (e.g., clays) into suspension in the water. Sheetwash, unchannelled flow across a surface carries suspended material away, and channels erode right through the soil layer, removing both fine and coarse material.

Wind erosion is exacerbated by the removal of trees that act as windbreaks and by agricultural practices that leave bare soil exposed.

Tillage is also a factor in soil erosion, especially on slopes, because each time the soil is lifted by a cultivator, it is moved a few centimeters down the slope.

4.4 Mass Wasting

Mass wasting, which is synonymous with “slope failure,” is the failure and downslope movement of rock or unconsolidated materials in response to gravity. The term “landslide” is almost synonymous with mass wasting, but not quite because some people reserve “landslide” for relatively rapid slope failures, while others do not. Other than the video below, this textbook will avoid using the term “landslide.”

Factors That Control Slope Stability

Mass wasting happens because tectonic processes have created uplift. Erosion, driven by gravity, is the inevitable response to that uplift, and various types of erosion, including mass wasting, have created slopes in the uplifted regions. Slope stability is ultimately determined by two factors: the angle of the slope and the strength of the materials on it.

A block of rock is typically situated on a rock slope that is being pulled toward Earth’s center (vertically down) by gravity. The vertical gravitational force can be split into two components relative to the slope: one pushing the block down the slope (the shear force), and the other pushing into the slope (the normal force). The shear force, which wants to push the block down the slope, has to overcome the strength of the connection between the block and the slope, which may be quite weak if the block has split away from the main body of rock, or may be very strong if the block is still a part of the rock. If the shear strength is greater than the shear force, the block should not move. But if the shear force becomes stronger than the shear strength, the block of rock will slide down the slope.

As already noted, slopes are created by uplift followed by erosion. In areas with relatively recent uplift, slopes tend to be quite steep. This is especially true where glaciation has taken place because glaciers in mountainous terrain create steep-sided valleys. In areas without recent uplift, slopes are less steep because hundreds of millions of years of erosion (including mass wasting) have made them that way. However, as we will see, some mass wasting can happen even on relatively gentle slopes.

The strength of the materials on slopes can vary widely. Solid rocks tend to be strong, but there is an extensive range of rock strength. If we consider just the strength of the rocks, and ignore issues like fracturing and layering, then most crystalline rocks, like granite, basalt, or gneiss, are very strong, while some metamorphic rocks, like schist, are moderately strong. Sedimentary rocks have variable strength. Dolostone and some limestone are strong, most sandstone and conglomerate are moderately strong, and some sandstone and all mudstones are quite weak.

Fractures, metamorphic foliation, or bedding can significantly reduce the strength of a body of rock, and in the context of mass wasting, this is most critical if the planes of weakness are parallel to the slope and least critical if they are perpendicular to the slope.

Internal variations in the composition and structure of rocks can significantly affect their strength. Schist, for example, may have layers that are rich in sheet silicates (mica or chlorite) and these will tend to be weaker than other layers. Some minerals tend to be more susceptible to weathering than others, and the weathered products are commonly quite weak (e.g., the clay formed from feldspar).

Unconsolidated sediments are generally weaker than sedimentary rocks because they are not cemented and, in most cases, have not been significantly compressed by overlying materials. This binding property of sediment is sometimes referred to as cohesion. Sand and silt tend to be particularly weak, clay is generally a little stronger, and sand mixed with clay can be stronger still. Finer deposits are relatively strong (they maintain a steep slope), while the overlying sand is relatively weak, and has a shallower slope that has recently failed. Glacial till, typically a mixture of clay, silt, sand, gravel, and larger clasts, forms and is compressed beneath tens to thousands of meters of glacial ice so it can be as strong as some sedimentary rock.

Apart from the type of material on a slope, the amount of water that the material contains is the most important factor controlling its strength. This is especially true for unconsolidated materials, but it also applies to bodies of rock. Granular sediments, like the sand at Point Grey, have lots of spaces between the grains. Those spaces may be completely dry (filled only with air); or moist (often meaning that some spaces are water filled, some grains have a film of water around them, and small amounts of water are present where grains are touching each other); or completely saturated. Unconsolidated sediments tend to be strongest when they are moist because the small amounts of water at the grain boundaries hold the grains together with surface tension. Dry sediments are held together only by the friction between grains, and if they are well sorted or well rounded, or both, that cohesion is weak. Saturated sediments tend to be the weakest of all because the large amount of water pushes the grains apart, reducing the mount friction between grains. This is especially true if the water is under pressure.

Water will also reduce the strength of solid rock, especially if it has fractures, bedding planes, or clay-bearing zones. This effect is even more significant when the water is under pressure, which is why holes are drilled into rocks on road cuts to relieve this pressure.

Moreover, finally, water can significantly increase the mass of the material on a slope, which increases the gravitational force pushing it down. A body of sediment that has 25% porosity and is saturated with water weighs approximately 13% more than it does when it is completely dry, so the gravitational shear force is also 13% higher.

4.5 Classification of Mass Wasting

It is important to classify slope failures so that we can understand what causes them and learn how to mitigate their effects. The three criteria used to describe slope failures are:

The type of motion is the essential characteristic of slope failure, and there are three different types of motion:

Major types of mass wasting and their physical characteristics from the USGS.

Unfortunately, it is not typically that simple. Many slope failures involve two of these types of motion, some involve all three, and in many cases, it is not easy to tell how the material moved.

Rock Fall

Rock fragments can break off relatively easily from steep bedrock slopes, most commonly due to frost-wedging in areas where there are many freeze-thaw cycles per year. When hiking along a steep mountain trail on a cool morning, one might have heard the occasional fall of rock fragments onto a talus slope. This happens because the water between cracks freezes and expands overnight, and then when that same water thaws in the morning sun, the fragments that had been pushed beyond their limit by the ice fall to the slope below.

Rock fall in Jalalabad, Afghanistan.

Rock Slide

A rock slide is the sliding motion of rock along a sloping surface. In most cases, the movement is parallel to a fracture, bedding, or metamorphic foliation plane, and it can range from very slow to moderately fast. The word sackung describes the very slow motion of a block of rock (mm/y to cm/y) on a slope.

Rock slide

Rock Avalanche

If a rock slides and then starts moving quickly (m/s), the rock is likely to break into many small pieces, and at that point it turns into a rock avalanche, in which the large and small fragments of rock move in a fluid manner supported by a cushion of air within and beneath the moving mass.

Goodell Creek rock avalanche, November 25, 2008.

Creep or Solifluction

The very slow, millimeters per year to centimeters per year, movement of soil or other unconsolidated material on a slope is known as creep. Creep, which generally only affects the upper several centimeters of loose material, is typically a very slow flow, but in some cases, sliding may take place. Creep can be facilitated by freezing and thawing because particles are lifted perpendicular to the surface by the growth of ice crystals within the soil, and then let down vertically by gravity when the ice melts. The same effect can be produced by frequent wetting and drying of the soil. In cold environments, solifluction is a more intense form of freeze-thaw-triggered creep.

Creep is most noticeable on moderate-to-steep slopes where trees, fence posts, or grave markers are consistently leaning in a downhill direction. In the case of trees, they try to correct their lean by growing upright, and this leads to a curved lower trunk known as a “pistol butt.”

Soil creep below Morgan’s Hill. Image taken by Derek Harper.


Slump is a type of slide (movement as a mass) that takes place within thick unconsolidated deposits (typically thicker than 10 m). Slumps involve movement along one or more curved failure surfaces, with downward motion near the top and outward motion toward the bottom. They are typically caused by an excess of water within these materials on a steep slope.

Mudflows and Debris Flows

When a mass of sediment becomes completely saturated with water, the mass loses strength, to the extent that the grains are pushed apart, and it will flow, even on a gentle slope. This can happen during rapid spring snowmelt or heavy rains, and is also relatively common during volcanic eruptions because of the rapid melting of snow and ice. (A mudflow or debris flow on a volcano or during a volcanic eruption is a lahar.) If the material involved is primarily sand-sized or smaller, it is known as a mudflow.

If the material involved is gravel-sized or larger, it is known as a debris flow. Because it takes more gravitational energy to move larger particles, a debris flow typically forms in an area with steeper slopes and more water than does a mudflow. In many cases, a debris flow takes place within a steep stream channel, and is triggered by the collapse of bank material into the stream. This creates a temporary dam, and then a significant flow of water and debris when the dam breaks.

The United States Geologic Survey and the Utah Geologic Survey are excellent sources for more information regarding mass wasting.

4.6 Erosion

Erosion is a mechanical process, usually driven by water, gravity, wind, or ice that removes sediment from the place of weathering. Liquid water is the principal agent of erosion. Erosion resistance is essential in the creation of distinctive geological features. This is well demonstrated in the cliffs of the Grand Canyon. The cliffs are made of rock left standing after less resistant materials have weathered and eroded. Rocks with different levels of erosion resistant also create the unique-looking features called hoodoos in Bryce Canyon National Park and Goblin Valley State Park in Utah.

Bryce Canyon in October 2018. Image by R. Adam Dastrup.

Erosion by Streams

Streams, any running water from a rivulet to a raging river, complete the hydrologic cycle by returning precipitation that falls on land to the oceans. Some of this water moves over the surface and some moves through the ground as groundwater. Flowing water does the work of both erosion and deposition.


Flowing streams pick up and transport weathered materials by eroding sediments from their banks. Streams also carry ions and ionic compounds that dissolve easily in the water. Sediments are carried as the following loads: dissolved, suspended, and bed. A dissolved load is composed of ions in solution. These ions are usually carried in the water all the way to the ocean.

Sediments carried as solids as the stream flows are called a suspended load. The size of particles that can be carried within a load is determined by the stream’s velocity. Faster streams can carry larger particles. Streams that carry larger particles have greater competence. Streams with a steep gradient (slope) have a faster velocity and greater competence.

Stream-cross section showing stream load.

Particles that are too large to be carried as suspended loads are bumped and pushed along the stream bed, called bed load. Bed load sediments do not move continuously, but rather in intermittent movements, called saltation. Streams with high velocities and steep gradients do a great deal of down cutting into the stream bed, which is primarily accomplished by movement of particles that make up the bed load.


As a stream flows from higher elevations, like in the mountains, towards lower elevations, like the ocean, the work of the stream changes. At a stream’s headwaters, often high in the mountains, gradients are steep. The stream moves fast and does lots of work eroding the stream bed.

As a stream moves into lower areas, the gradient is not as steep. Now the stream does more work eroding the edges of its banks. Many streams develop curves in their channels called meanders. As streams move onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain, which is a flat level area surrounding the stream channel.

The base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond. Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach the base level and the more cutting it has to do.

As a stream gets closer to the base level, its gradient lowers, and it deposits more material than it erodes. On flatter ground, streams deposit material on the inside of meanders. A stream’s floodplain is much broader and shallower than the stream’s channel. When a stream flows onto its floodplain, its velocity slows, and it deposits much of its load. These sediments are rich in nutrients and make excellent farmland.

Alluvial fan in Iran. Image source: NASA.

A stream at flood stage carries lots of sediments. When its gradient decreases, the stream overflows its banks and broadens its channel. The decrease in gradient causes the stream to deposit its sediments, the largest first. These large sediments build a higher area around the edges of the stream channel, creating natural levees.

Lena River Delta by Landsat 7. Image source: NASA.

When a river enters standing water, its velocity slows to a stop. The stream moves back and forth across the region and drops its sediments in a wide triangular-shaped deposit called a delta. If a stream falls down a steep slope onto a broad flat valley, an alluvial fan develops. Alluvial fans generally form in arid regions.


The Nile River and delta as seen from space by the MODIS sensor on the Terra satellite. Image by NASA.

Ground Water Erosion

Groundwater is a strong erosional force, as it works to dissolve away solid rock. Carbonic acid is especially good at dissolving the rock limestone. Over many years, groundwater travels along small cracks. The water dissolves and carries away the solid rock gradually enlarging the cracks, eventually forming a cave. The video below is drone footage of the world’s largest cave, Hang Son Doong, in Vietnam.

Groundwater carries the dissolved minerals in solution. The minerals may then be deposited, for example, as stalagmites (grows from the top) or stalactites (grows from the bottom). If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these fantastic and strangely captivating structures. Caves also produce a beautiful rock, formed from calcium carbonate, travertine. Groundwater saturated with calcium carbonate precipitates as the mineral calcite or aragonite. Mineral springs that produce travertine can be hot, warm or even cold.

If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood.

Wave Action and Erosion

Waves are essential for building up and breaking down shorelines. Waves transport sand onto and off of beaches, transport sand along beaches, carves structures along the shore. The most massive waves form when the wind is very strong, blows steadily for a long time, and blows over a long distance.

Wave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales.

The wind could be strong, but if it gusts for just a short time, large waves will not form. Wave energy does the work of erosion at the shore. Waves approach the shore at some angle, so the inshore part of the wave reaches shallow water sooner than the part that is further out. The shallow part of the wave ‘feels’ the bottom first. This slows down the inshore part of the wave and makes the wave ‘bend.’ This bending is called refraction.

Wave refraction either concentrates wave energy or disperses it. In quiet water areas, such as bays, wave energy is dispersed, so sand is deposited. Areas that stick out into the water are eroded by the intense wave energy that concentrates its power on the wave-cut cliff.

A wave-cut platform is the level area formed by wave erosion as the waves undercut a cliff. An arch is produced when waves erode through a cliff. When a sea arch collapses, the isolated towers of rocks that remain are known as sea stacks.

Durdle Door (sometimes written Durdle Dor) is a natural limestone arch on the Jurassic Coast near Lulworth in Dorset, England. Image by Phil Dolby.


Rivers carry sediments from the land to the sea. If wave action is high, a delta will not form. Waves will spread the sediments along the coastline to create a beach. Waves also erode sediments from cliffs and shorelines and transport them onto beaches.

Beaches can be made of mineral grains, like quartz, rock fragments, and also pieces of shell or coral. Waves continually move sand along the shore and move sand from the beaches on shore to bars of sand offshore as the season’s change. In the summer, waves have lower energy, so they bring sand up onto the beach. In the winter, higher energy waves bring the sand back offshore.

Some features form by wave-deposited sand. These features include barrier islands and spits. A spit is sand connected to the land and extending into the water. A spit may hook to form a tombolo. Shores that are relatively flat and gently sloping may be lined with long narrow barrier islands. Most barrier islands are a few kilometers wide and tens of kilometers long.

In its natural state, a barrier island acts as the first line of defense against storms such as hurricanes. When barrier islands are urbanized, hurricanes damage houses and businesses rather than vegetated sandy areas in which sand can move. A large hurricane brings massive problems to the urbanized area.


Intact shore areas protect inland areas from storms that come off the ocean. Where the natural landscape is altered, or the amount of development does damage from a storm too costly to consider, people use several types of structures to attempt to slow down wave erosion. A groin is a long narrow pile of rocks built perpendicular to the shoreline to keep sand at that beach. A breakwater is a structure built in the water parallel to the shore in order to protect the shore from strong incoming waves. A seawall is also parallel to the shore, but it is built onshore.

Aerial image of Siloso Beach in Singapore.

People do not always want to choose safe building practices, and instead choose to build a beach house right on the beach. Protecting development from wave erosion is difficult and expensive, and it does not always work. The northeastern coast of Japan was protected by anti-tsunami seawalls, yet waves from the 2011 tsunami that resulted from the Tohoku earthquake washed over the top of some seawalls and caused others to collapse. Japan is now planning to build even higher seawalls to prepare for any future (and inevitable) tsunami.

4.7 Transport of Particles by Wind

The power of wind to erode depends on particle size, wind strength, and whether the particles can be picked up. Wind is a more important erosional force in arid than humid regions. Wind transports small particles, such as silt and clay, over great distances, even halfway across a continent or an entire ocean basin. Particles may be suspended for days. Wind more easily picks up particles on the ground that has been disturbed, such as a construction site or a dune.

wind erosion

Wind is a stronger erosional force in arid regions than it is in humid regions. In humid areas, water and vegetation bind the soil, so it is harder to pick up. In arid regions, small particles are selectively picked up and transported. As they are removed, the ground surface gets lower and rockier, causing deflation. What is left is desert pavement, a surface covered by gravel-sized particles that are not easily moved by wind.

Particles moved by wind do the work of abrasion. As a grain strikes another grain or surface, it erodes that surface. Abrasion by wind may polish natural or human-made surfaces, such as buildings. Stones that have become polished and faceted due to abrasion by sand particles are called ventifacts.

Exposed rocks in desert areas often develop a dark brown to black coating called desert varnish. Wind transports clay-sized particles that chemically react with other substances at high temperatures. The coating is formed of iron and manganese oxides. Often petroglyphs are carved into the desert varnish by earlier civilizations in arid regions.

A rock sculpted by wind erosion in the Altiplano region of Bolivia.

4.8 Glacial Influence on Erosion

Formation and Movement of Glaciers

Glaciers cover about 10 percent of the land surface near Earth’s poles, and they are also found in high mountains. During the Ice Ages, glaciers covered as much as 30 percent of Earth. Around 600 to 800 million years ago, geologists think that almost all of the Earth was covered in snow and ice, called the Snowball Theory. Scientists use the evidence of erosion and deposition left by glaciers to do a kind of detective work to figure out where the ice once was and where it came from.

Glaciers are solid ice that moves exceptionally slowly along the land surface. They erode and shape the underlying rocks. Glaciers also deposit sediments in characteristic landforms. The two types of glaciers are: continental and alpine. Continental glaciers are large ice sheets that cover relatively flat ground. These glaciers flow outward from where the most considerable amount of snow and ice accumulate. Alpine or valley glaciers flow downhill through mountains along existing valleys.


Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock, the water freezes and pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier. With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock making long, parallel grooves in the bedrock, called glacial striations.

Mountain glaciers leave behind unique erosional features. When a glacier cuts through a ‘V’ shaped river valley, the glacier pucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a ‘U’ shaped valley.

Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower ‘U’ shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls. Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls.


Agriculture, U. S. D. of. (2018). Soil in hand for planting [Photo]. Retrieved from
Arbol de Piedra. (n.d.). Retrieved from
Atlas Pro. (n.d.). How Do Caves Form? Retrieved from
bikram79. (n.d.). Planet Earth Caves. Retrieved from
Bryce Canyon National Park (U.S. National Park Service). (n.d.). Retrieved February 16, 2019, from
CNN. (n.d.). Greenland is Melting. Retrieved from
CrashCourse. (n.d.). Nitrogen & Phosphorus Cycles: Always Recycle! Part 2 – Crash Course Ecology #9. Retrieved from
Death Valley Sand Dunes. (n.d.). Retrieved from
dimitris.g. (2015). Sunday Morning – Skala Oropou, Greece [Photo]. Retrieved from
Erosion and Deposition | CK-12 Foundation. (n.d.). Retrieved February 16, 2019, from
Exposure Labs. (n.d.). “CHASING ICE” captures largest glacier calving ever filmed – OFFICIAL VIDEO. Retrieved from
G310Luke. (2008). Goodell Creek Debris Avalanche. Retrieved from
Galuzzi, L. (n.d.). Bryce Canyon. Retrieved February 16, 2019, from
Goblin Valley State Park. (n.d.). Retrieved February 16, 2019, from
Harper, D. (2009). Terracettes below Morgan’s Hill. Retrieved from
Hazards – Utah Geological Survey. (n.d.). Retrieved February 16, 2019, from
Landslides & Rock Falls – Utah Geological Survey. (n.d.). Retrieved February 16, 2019, from
Lena River. (2019). Retrieved from
Malaspina Glacier, Alaska. (n.d.). Retrieved from
Mass Wasting – Physical Geology. (n.d.). Retrieved February 16, 2019, from
Morbihan Iile Berder Rankosol Granite. (n.d.). Retrieved from
MSNBC. (n.d.). Amazing Drone Video Of World’s Largest Cave | msnbc. Retrieved from
National Geographic. (n.d.-a). Climate 101: Glaciers | National Geographic. Retrieved from
National Geographic. (n.d.-b). He’s Watching This Glacier Melt Before His Eyes | Short Film Showcase. Retrieved from
National Geographic. (n.d.-c). Landslides | National Geographic. Retrieved from
Nitrogen Cycle. (n.d.). Retrieved from
NOVA PBS Official. (n.d.). Greenland Melting (360°). Retrieved from
Rabich, D. (2014). Deutsch: Wegekreuz am Kettbach, Hausdülmen, Dülmen, Nordrhein-Westfalen, Deutschland. Retrieved from,_Wegekreuz_am_Kettbach_–_2014_–_3036.jpg
Siloso Beach Sentosa Singapore. (n.d.). Retrieved from
Soil Profile. (n.d.). Retrieved from
Storyful News. (n.d.). Amazing Footage of Debris Flow in Illgraben. Retrieved from
Talus ConesIsfjorden. (n.d.). Retrieved February 16, 2019, from
Tanyaş, H., Allstadt, K. E., & van Westen, C. J. (2018). An updated method for estimating landslide-event magnitude: An updated method for estimating landslide-event magnitude. Earth Surface Processes and Landforms, 43(9), 1836–1847.
The Telegraph. (n.d.). What Causes a Landslide? Retrieved from
Types of landslide profiles. (n.d.). Retrieved February 16, 2019, from
US EPA. (n.d.). Retrieved February 16, 2019, from
USDA. (n.d.). Retrieved February 16, 2019, from | Science for a changing world. (n.d.). Retrieved February 16, 2019, from
Utah Geological Survey – Keeping Utah informed with geologic data. (n.d.). Retrieved February 16, 2019, from
Wavecut Platform Southerndown. (n.d.). Retrieved from
Weathering and Formation of Soil | CK-12 Foundation. (n.d.). Retrieved February 16, 2019, from
Weathering and Soil – Physical Geology. (n.d.). Retrieved February 16, 2019, from
Weathering, Erosion, and Sedimentary Rocks – An Introduction to Geology. (n.d.). Retrieved February 16, 2019, from
Wien, S. D. (2007). Deutsch: Steinschlag an der „Jalalabad Road“ zwischen Kabul und Dschalalabad, AfghanistanEnglish: Jalalabad Rd., highway from Kabul to Surobi and Jalalabad, Afghanistan. Retrieved from
Zell, H. (2013, June 6). Canyons and Glaciers Along the Northwest Coast of Greenland. Retrieved February 16, 2019, from

Chapter 5 Weather and climate for print only


5.1 Defining Climate and Weather

When it comes to defining climate, it is often said that “climate is what you expect; weather is what you get.” That is to say; climate is the statistically-averaged behavior of the weather. In reality, it is a bit more complicated than that, as climate involves not just the atmosphere, but the behavior of the entire climate system—the complex system defined by the coupling of the atmosphere, oceans, ice sheets, and biosphere. Weather is the current conditions of the atmosphere for a specific location and time.

Having defined climate, we can begin to define what climate change means. While the notion of climate is based on some statistical average of the behavior of the atmosphere, oceans, etc., this average behavior can change over time. That is to say, what you “expect” of the weather is not always the same. For example, during El Niño years, we expect it to be wetter in the winter in California and snowier in the southeastern U.S., and we expect fewer tropical storms to form in the Atlantic during the hurricane season. So, the climate itself varies over time.

If climate is always changing, then is climate change by definition always occurring? Yes and No. A hundred million years ago, during the early part of the Cretaceous period, dinosaurs roamed a world that was almost certainly warmer than today. The geological evidence suggests, for example, that there was no ice even at the North and South poles. So global warming can happen naturally, right? Certainly, but why was the Earth warmer at that time?

So, the significant climate changes in Earth’s geologic past were closely tied to changes in the greenhouse effect. Those changes were natural. The changes in greenhouse gas concentrations that scientists talk about today are, however, not natural. They are due to human activity.

The scientific consensus demonstrates that climate change in the 21st century is necessarily a human problem. People are causing climate change through their everyday actions and the socioeconomic forces underlying those actions. At the same time, people are feeling the consequences of climate change through various impacts on things they value and through the responses they are making to address climate change.

Climate is the average of weather (typically precipitation and temperature) in a particular location over a long period, usually for at least 30 years. A location’s climate can be described by its air temperature, humidity, wind speed and direction, and the type, quantity, and frequency of precipitation. Climate can change, but only over long periods of time. The climate of a region depends on its position relative to many things.

The Climate System

The climate system is comprised of five natural components: atmosphere, hydrosphere, cryosphere, land surface, and biosphere. The atmosphere is the envelope of gases that surrounds Earth, including the naturally occurring greenhouse gases that warm the planet’s surface. The hydrosphere includes all of Earth’s liquid water and gaseous water (water vapor), whereas the cryosphere includes all frozen water (ice). Note that the cryosphere is technically part of the hydrosphere, but climate scientists usually treat it as a separate component of the climate system because its physical properties differ from those of water and water vapor. The land surface does not include water- or ice-covered surfaces but consists of all other vegetated and non-vegetated surfaces. The biosphere is the realm of life and is found in all of the other natural components, especially the hydrosphere and land surface. The biota is made up of and requires the presence of air, water, and mineral matter – that is, material from the atmosphere, hydrosphere, and land – to exist. Several external forces influence the five climate system components, with radiation from the Sun being most important. Climate scientists consider the impact of human activities on the climate system another example of external forcing.

Why Understanding Climate is Important

Everything in the lighter shading would be flooded in the transition from the ice age to pre-industrial modern climate. But what sort of effort would that have taken? It turns out that the natural increase in atmospheric carbon dioxide that led to the thaw after the last Ice Age was an increase from 180 parts per million (ppm) to about 280 ppm. This was a smaller increase than the present-time increase due to human activities, such as fossil fuel burning, which thus far have raised carbon dioxide levels from the pre-industrial value of 280 ppm to a current level of over 400 ppm–a level which is increasing by 2 ppm every year. So, arguably, if the dawn of industrialization had occurred 18,000 years ago, we may very likely have sent the climate from an ice age into the modern pre-industrial state.

How long it would have taken to melt all of the ice is not precisely known, but it is conceivable it could have happened over a period as short as two centuries. The area ultimately flooded would be considerably larger than that currently projected to flood due to the human-caused elevation of carbon dioxide that has taken place so far. The hypothetical city of “Old Orleans” would have to be relocated from its position in the Gulf of Mexico 100+ miles off the coast of New Orleans to the current location of “New Orleans”.

By some measures, human interference with the climate back then, had it been possible, would have been even more disruptive than the current interference with our climate. Yet that interference would simply be raising global mean temperatures from those of the last Ice Age to those that prevailed in modern times prior to industrialization. What this thought experiment tells us is that the issue is not whether some particular climate is objectively “optimal”. The issue is that human civilization, natural ecosystems, and our environment are heavily adapted to a particular climate — in our case, the current climate. Rapid departures from that climate would likely exceed the adaptive capacity that we and other living things possess, and cause significant consequent disruption in our world.

5.2 Controls of Climate

The climate system reflects an interaction between a number of critical sub-systems or components. In this chapter, we will focus on the components most relative to modern climate change: the atmosphere, hydrosphere, cryosphere, and biosphere. The atmosphere is, of course, a critical component of the climate system, and the one we will spend the most time talking about.

Composition of the Atmosphere

The atmosphere is mostly nitrogen and oxygen, with trace amounts of other gases. Most atmospheric constituents are well mixed, which is to say, these constituents vary in constant relative proportion, owing to the influence of mixing and turbulence in the atmosphere. The assumption of a well-mixed atmosphere and the assumption of ideal gas behavior were both implicit in our earlier derivation of the exponential relationship of pressure with height in the atmosphere.

The composition of the atmosphere.

There are, of course, exceptions to these assumptions. Ozone is primarily found in the lower stratosphere (though some are produced near the surface as a consequence of photochemical smog). Some gases, such as methane, have reliable sources and sinks and are therefore highly variable as a function of region and season.

Atmospheric water vapor is highly variable in its concentration, and, undergoes phase transitions between solid, liquid, and solid form during normal atmospheric processes (i.e., evaporation from the surface, and condensation in the form of precipitation as rainfall or snow).

Of particular significance in considerations of atmospheric composition are greenhouse gases (carbon dioxide, water vapor, methane, and some other trace gases) because of their radiative properties and, precisely, their role in the greenhouse effect. The greenhouse effect is the process by which radiation from Earth’s atmosphere warms the surface of the planet to a temperature above what it would be without the atmosphere.

If a planet’s atmosphere contains greenhouse gases, it will radiate energy in all directions. Part of this radiation is directed towards the surface, warming it. The strength and intensity of the greenhouse effect will depend on the atmosphere’s temperature and on the number of greenhouse gases that the atmosphere contains.


The term “greenhouse effect” is a misnomer that arose from a faulty analogy with the effect of sunlight passing through glass and warming a greenhouse. The way a greenhouse retains heat is fundamentally different, as a greenhouse works mostly by reducing airflow, so that warm air is kept inside.


Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in longer wavelengths (12–15 micrometers) that water vapor does not, partially closing the “window” through which heat radiated by the surface would normally escape to space.


Earth’s natural greenhouse effect is critical to supporting life. Human activities, mainly the burning of fossil fuels and clearing of forests, have strengthened the greenhouse effect and caused global warming.

Seasonal and latitudinal dependence of energy balance

The Earth’s climate is a solar powered system. So to truly understand Earth’s climate, an understanding of the planet’s energy balance is essential. An interactive animation provided below allows you to explore the balance of incoming and outgoing sources of energy within the climate system. A brief tutorial is provided below, first with the short wave component and then the longwave component of the energy budget.

Now explore these animations by yourself, at your own pace. It takes some time to absorb all of the information that is contained here. Start with the short wave energy budget. Once you are satisfied that you have got that down, go on to the somewhat more complex longwave energy budget by clicking the button at the end of the first animation.

Consider how incoming and outcoming energy sources of shortwave and longwave radiation achieve a net balance:


Next, let us note that the above picture represents average climate conditions, that is, averaged over the entire Earth’s surface, and averaged over time. However, in reality, the incoming distribution of radiation varies in both space and time. We measure the radiation in terms of power (energy per unit time) per unit area, a quantity we term intensity or energy flux, which can be measured in watts per square meter (W/m2).

The dominant spatial variation occurs with latitude. On average, there is roughly 343 W/m2 of incoming shortwave solar radiation that is incident on the Earth, averaged over time, and the Earth surface area. There is more incoming solar radiation arriving at the surface near the equator than near the poles. On average, roughly 30 percent, or about 100 W/m2 of this incident radiation is reflected out to space by clouds and reflective surfaces of the Earth, such as ice and desert sand, leaving roughly 70 percent of the incoming solar radiation to be absorbed by the Earth’s surface. The portion that is reflected by clouds and by the surface also varies substantially with latitude, owing to the latitudinal variations in cloud and ice cover.

Compared to equatorial regions (b), incoming solar radiation of the polar regions (a) is less intense for two reasons: 1) the solar radiation arrives at an oblique angle nearer the poles, so that the energy spreads over a larger surface area, lessening its intensity, 2) the radiation travels a longer distance through the atmosphere, which absorbs, scatters and reflects the solar radiation.


The solar radiation received at Earth’s surface varies by time and latitude. This graph illustrates the relationship between latitude, time, and solar energy during the equinoxes. The illustrations show how the time of day (A-E) affects the angle of incoming sunlight (revealed by the length of the shadow) and the light’s intensity. On the equinoxes, the Sun rises at 6:00 a.m. everywhere. The strength of sunlight increases from sunrise until noon, when the Sun is directly overhead along the equator (casting no shadow). After noon, the strength of sunlight decreases until the Sun sets at 6:00 p.m. The tropics (from 0 to 23.5° latitude) receive about 90% of the energy compared to the equator, the mid-latitudes (45°) roughly 70%, and the Arctic and Antarctic Circles about 40 percent.

It is also worth noting that the incoming solar radiation is not constant in time. The output of the Sun, called solar constant, can vary by small amounts on timescales of decades and longer. During the Earth’s early evolution, billions of year ago, the Sun was probably about 30 percent less bright than it is today – indeed, explaining how the Earth’s climate could have been warm enough to support life back then remains somewhat of a challenge, known as the “Faint Young Sun” paradox.

Even more dramatic changes in solar insolation take place on shorter timescales – the diurnal and annual timescale. These changes, however, do not have to do with the net output of the Sun, but rather the distribution of solar insolation over the Earth’s surface. This distribution is influenced by the Earth’s daily rotation about its axis, which of course leads to night and day, and the annual orbit of the Earth about the Sun, which leads to our seasons. While there is a small component of the seasonality associated with changes in the Earth-Sun distance during the course of the Earth’s annual orbit about the Sun (because of the slightly elliptical nature of the orbit), the primary reason for the seasons is the tilt of Earth’s rotation axis relative to the plane defined by the Earth and the Sun, which causes the Northern Hemisphere and Southern Hemisphere to be preferentially oriented either towards or away from the Sun, depending on the time of year.

The consequence of all of this is that the amount of shortwave radiation received from the Sun at the top of the Earth’s atmosphere varies as a function of both times of day and season. Subtle changes in the Earth’s orbital geometry (i.e., changes in the tilt of the axis, the degree of ellipticity of the orbit, and the slow precession of the orbit) are responsible for the coming and going of the ice ages over tens of thousands of years.


We have seen above that the distribution of solar insolation over the Earth’s surface changes over the course of the seasons, with the Sun, in a relative sense, migrating south and then north of the equator over the course of the year – that annual migration, between 23.5 degrees S and 23.5 degrees N, defines the region we call the tropics. As the heating by the Sun migrates south and north within the tropics over the course of the year, so does the tendency for rising atmospheric motion. As we have seen, warmer air is less dense than cold air, and where the Sun is heating the surface, there is a tendency for convective instability, i.e., the unstable situation of having relatively light air underlying relatively heavy air. Where that instability exists, there is a tendency for rising motion in the atmosphere, as the warm air seeks to rise above the colder air. As a result, there is a tendency for rising air (and with it, rainfall) in a zone of low surface pressure known as the Intertropical Convergence Zone or ITCZ, which is centered roughly at the equator, but shifts north and south with the migration of the Sun about the equator over the course of the year. Due to the greater thermal inertia of the oceans relative to the land surface, the response to the shifting solar heating is more sluggish over the ocean, and the ITCZ shows less of a latitudinal shift with the seasons. By contrast, over the most extensive land masses (e.g., Asia), the seasonal shifts can be quite pronounced, resulting in dramatic shifts in wind and rainfall patterns such as the Indian monsoon.


The air rising in the tropics then sinks in the subtropics, forming a subtropical band of high surface pressure and low precipitation associated with the prevailing belt of deserts in the subtropics of both hemispheres. The resulting pattern of circulation of the atmosphere is known as the Hadley Cell circulation. In sub-polar latitudes, there is another region of low surface pressure, associated again with rising atmospheric motion and rainfall. This region is known as the polar front. These belts of high and low atmospheric surface pressure and the associated patterns of atmospheric circulation also shift south and north over the course of the year in response to the heating by the Sun.

We have seen above that there is an imbalance between the absorbed incoming short wave solar radiation and the emitted outgoing longwave terrestrial radiation, with a relative surplus within the tropics and a relative deficit near the poles. We, furthermore, noted that the atmosphere and ocean somehow relieve this imbalance by transporting heat laterally, through a process known as heat advection. We are now going to look more closely at how the atmosphere accomplishes this transport of heat. We have already seen one crucial ingredient, namely the Hadley Cell circulation, which has the net effect of transporting heat poleward from where there is a surplus to where there is a deficit.

Wind patterns in the extratropics also serve to transport heat poleward. The lateral wind patterns are primarily governed by a balance between the previously discussed pressure gradient force (acting in this case laterally rather than vertically), and the Coriolis force, a compelling force that exists because the Earth is itself rotating. This balance is known as the geostrophic balance.

The Coriolis force acts at right angles to the direction of motion: 90 degrees to the right in the Northern Hemisphere and 90 degrees to the left in the Southern Hemisphere. The pressure gradient force is directed from regions of high surface pressure to regions of low surface pressure. As a consequence, geostrophic balance leads to winds in the mid-latitudes, between the subtropical high-pressure belt and the sub-polar low-pressure belt of the polar front, blowing from west to east. We call these westerly winds. For reasons that have to do with the vertical thermal structure of the atmosphere, and the combined effect of the geostrophic horizontal force balance and hydrostatic vertical force balance in the atmosphere, the westerly winds become stronger aloft, leading to the intense regions of high wind known as the jet streams in the midlatitude upper troposphere.

Conversely, winds in the tropics tend to blow from east to west. These are known as easterly winds or, by the perhaps more familiar term, the trade winds. In the Northern Hemisphere, geostrophic balance implies counter-clockwise rotation of winds about low-pressure centers and clockwise rotation of winds about high-pressure centers. The directions are opposite in the Southern Hemisphere.

Due to the effect of friction at the Earth’s surface, there is an additional component to the winds which blows out from high-pressure centers and in towards low-pressure centers. The result is spiraling in (convergence) towards low-pressure centers and a spiraling out (divergence) about high-pressure centers. The convergence of the winds toward the low-pressure centers is associated with the rising atmospheric motion that occurs within regions of low surface pressure. The divergence of the winds away from the high-pressure centers is associated with the sinking atmospheric motion that occurs within regions of high atmospheric pressure.

The inward spiraling low-pressure systems in mid-latitudes constitute the polar front, which separates the coldest air masses near the poles from the warmer air masses in the subtropics. It is the unstable property of having clashing air masses with vastly different temperature characteristics, known as baroclinic instability, that is responsible for the existence of extratropical cyclones. The energy that drives the extratropical cyclones comes from the work done as surface air is lifted along frontal (i.e., cold front and warm front) boundaries. These extratropical storm systems relieve high-latitude deficit of radiation by mixing cold polar and warm subtropical air and, in so doing, transporting heat poleward, along with the latitudinal temperature gradient.


When a particular location is near a large body of water, the local climate will be directly impacted, creating a maritime climate. Temperatures typically vary only slightly across the day and year. For a location to have a true maritime climate, the winds must most frequently come off the sea.

When a particular location is not located near any large body of water, the region will typically experience a continental climate. A continental climate is more extreme, with more significant temperature differences between day and night and between summer and winter.

OCEAN circulation

While we have focused primarily on the atmosphere thus far, the oceans, too, play a crucial role in relieving the radiation imbalance by transporting heat from lower to higher latitudes. The oceans also play a crucial role in both climate variability and climate change, as we will see. There are two primary components of ocean circulation. The first component is the horizontal circulation, characterized by wind-driven ocean gyres.


The major surface currents are associated with ocean gyres. These include the warm poleward western boundary currents such as the Gulf Stream, which is associated with the North Atlantic Gyre, and the Kuroshio Current associated with the North Pacific Gyre. These gyres also contain cold equatorward eastern boundary currents such as the Canary Current in the eastern North Atlantic and the California Current in the western North Atlantic. Similar current systems are found in the Southern Hemisphere. The horizontal patterns of ocean circulation are driven by the alternating patterns of wind as a function of latitude, and, in particular, by the tendency for westerly winds in mid-latitudes and easterly winds in the tropics, discussed above.

An essential additional mode of ocean circulation is the thermohaline circulation, which is sometimes referred to as the meridional overturning circulation or MOC. The circulation pattern is shown below. By contrast with the horizontal gyre circulations, the MOC can be viewed as a vertical circulation pattern associated with a tendency for sinking motion in the high-latitudes of the North Atlantic, and rising motion more broadly in the tropics and subtropics of the Indian and Pacific ocean. This circulation pattern is driven by contrasts in density, which are, in turn, primarily due to variations in both temperature and salinity (hence the term thermohaline). The sinking motion is associated with relatively cold, salty surface waters of the subpolar North Atlantic, and the rising motion with the relatively warm waters in the tropical and subtropical Pacific and Indian ocean.


The picture presented above is a highly schematized and simple description of the actual vertical patterns of circulation in the ocean. Nonetheless, the conveyor belt is a useful mnemonic. The northward surface branch of this circulation pattern in the North Atlantic is sometimes erroneously called the Gulf Stream. The Gulf Stream, as discussed above, is part of the circulating waters of the wind-driven ocean gyre circulation. By contrast, the northward extension of the thermohaline circulation in the North Atlantic is rightfully referred to as the North Atlantic Drift. This current system represents a net transport of warm surface waters to higher latitudes in the North Atlantic and is also an essential means by which the climate system transports heat poleward from lower latitudes. Changes in this current system are speculated as having played a key role in past and potential future climate changes.


Atmospheric pressure and temperature decrease with altitude within the troposphere. The closer molecules are packed together, the more likely they are to collide. Collisions between molecules give off heat, which warms the air. At higher altitudes, the air is less dense, and air molecules are more spread out and less likely to collide. A location in the mountains has lower average temperatures than one at the base of the mountains. In Colorado, for example, Lakewood (5,640 feet) average annual temperature is 62 degrees F (17 degrees C), while Climax Lake (11,300 feet) is 42 degrees F (5.4 degrees C). Mountain ranges have two effects on the climate of the surrounding region. The first is something called the rain shadow effect, which brings warm, dry climate to the leeward side of a mountain range, as described in the Earth’s Atmosphere chapter. The second effect mountains have on climate systems is the ability to separate coastal regions from the rest of the continent. Since a maritime air mass may have trouble rising over a mountain range, the coastal area will have a maritime climate, but the inland area on the leeward side will have a continental climate.


5.3 Climate Zones and Biomes

A climate zone results from the climate conditions of an area: its temperature, humidity, amount and type of precipitation, and the season. A climate zone is reflected in a region’s natural vegetation. Perceptive travelers can figure out which climate zone they are in by looking at the vegetation, even if the weather is unusual for the climate on that day.

The significant factors that influence climate determine the different climate zones. In general, the same type of climate zone will be found at similar latitudes and in similar positions on nearly all continents, both in the Northern and Southern Hemispheres. The one exception to this pattern is the continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere land masses are not broad enough to produce a continental climate.

The most common system used to classify climatic zones is the Köppen classification system. This system is based on the temperature, the amount of precipitation, and the times of year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is used as an indicator of climate type.


A climate type and its plants and animals make up a biome. The organisms of a biome share specific characteristics around the world because their environment has similar advantages and challenges. The organisms have adapted to that environment in similar ways over time. For example, different species of cactus live on different continents, but they have adapted to the harsh desert in similar ways.

The Köppen classification system recognizes five major climate groups, each with a distinct capital letter A through E. Each lettered group is divided into subcategories. Some of these subcategories are forest (f), monsoon (m), and wet/dry (w) types, based on the amount of precipitation and season when that precipitation occurs.

Compare the Koppen Classification map above with the physical earth map below and compare the similarities.


Tropical Moist Climates (Group A)

Tropical Moist (Group A) climates are found in a band about 15 to 25 degrees North and South of the equator. Broadly speaking, these climates tend to have the following characteristics:

The wet tropics have almost no annual temperature variation and tremendous amounts of rainfall year round, between 175 and 250 cm (65 and 100 inches). These conditions support the tropical rainforest biome. Densely packed, broadleaf evergreen trees dominate tropical rainforests. These rainforests have the highest number of species or biodiversity of any ecosystem.

Tropical Climates


The tropical monsoon climate has very low precipitation for one to two months each year. Rainforests grow here because the dry period is short, and the trees survive off of soil moisture. This climate is found where the monsoon winds blow, primarily in southern Asia, western Africa, and northeastern South America.


The tropical wet and dry climate lies between about 5 and 20 degrees North and South latitude, around the location of the ITCZ. In the summer, when the ITCZ drifts northward, the zone is wet. In the winter, when the ITCZ moves toward the equator, the region is dry. This climate exists where strong monsoon winds blow from land to sea, such as in India.

Rainforests cannot survive the months of low rainfall, so the typical vegetation is savanna. This biome consists mostly of grasses, with widely scattered deciduous trees and rare areas of denser forests.

Dry Climates (Group B)

The Dry Climates (Group B) have less precipitation than evaporation. Dry climate zones cover about 26 percent of the world’s land area. Broadly speaking, these climates tend to have the following characteristics:

Desert Climate


Low-latitude, arid deserts are found between 15 degrees and 30 degrees North and South, where warm, dry air sinks at high-pressure zones. Vast deserts make up around 12 percent of the world’s lands.

In the Sonoran Desert of the southwestern United States and northern Mexico, skies are clear. The typical weather is sweltering summer days and cold winter nights. Although annual rainfall is less than 25 cm (10 inches), rain falls during two seasons. Pacific storms bring winter rains and monsoons bring summer rains. Since organisms do not have to go too many months without some rain, a unique group of plants and animals can survive in the Sonoran desert.


Higher latitude semi-arid deserts, also called steppe, are found in continental interiors or rainshadows. Semi-arid deserts receive between 20 and 40 cm (8 to 16 inches) of rain annually. The annual temperature range is broad. In the United States, the Great Plains, portions of the southern California coast, and the Great Basin are semi-arid deserts.

Moist Subtropical Mid-Latitude (Group C)

The Moist Subtropical Mid-latitude climates broadly speaking, have the following characteristics:



The Dry Summer Subtropical climate is found on the western sides of continents between 30 to 45 degrees North and South latitude. Annual rainfall is 30 to 90 cm (14 to 35 inches) most of which comes in the winter.

The climate is typical of coastal California, which sits beneath a summertime high pressure for about five months each year. Land and sea breezes make winters moderate and summers cool. Vegetation must survive long summer droughts. The scrubby, woody vegetation that thrives in this climate is called chaparral.


The Humid Subtropical climate zone is found mostly on the eastern sides of continents. Rain falls throughout the year with annual averages between 80 and 165 cm (31 and 65 inches). Summer days are humid and hot, from the lower 30’s up to 40 degrees Celsius (mid-80’s up to 104 degrees Fahrenheit). Afternoon and evening thunderstorms are common. These conditions are caused by warm tropical air passing over the hot continent. Winters are mild, but middle-latitude storms, called cyclones, may bring snow and rain. The southeastern United States, with its hot humid summers and mild, but frosty winters, is typical of this climate zone.


Marine West Coast climate zones line western North America between 40 degrees and 65 degrees North latitude, an area known as the Pacific Northwest. Ocean winds bring mild winters and cool summers. The temperature range, both daily and annually, is relatively small. Rain falls year-round, although summers are drier as the jet stream moves northward. Low clouds, fog, and drizzle are typical. In Western Europe, the climate covers a more extensive region since no high mountains are near the coast to block wind blowing off the Atlantic.

Humid Continental (Group D)

Continental (Group D) climates are found in most of the North American interior from about 40 degrees North to 70 degrees North.  Broadly speaking, these climates have the following characteristics:

Trees grow in continental climates, even though winters are frigid because the average annual temperature is relatively mild. Continental climates are not found in the Southern Hemisphere because of the absence of a continent vast enough to generate this effect.

Humid Continental Climate


The humid continental climates are found around the polar front in North America and Europe. In the winter, middle-latitude cyclones bring chilly temperatures and snow. In the summer, westerly winds bring continental weather and warm temperatures. The average July temperature is often above 20 degrees Celcius (70 degrees Fahrenheit) The region is typified by deciduous trees, which protect themselves in winter by losing their leaves.

The two variations of this climate are based on summer temperatures:


The subpolar climate is dominated by the continental polar air that masses over the frigid continent. Snowfall is light, but cold temperatures keep snow on the ground for months. Most of the approximately 50 cm (20 inches) of annual precipitation falls during summer cyclonic storms. The angle of the Sun’s rays is low, but the Sun is visible in the sky for most or all of the day during the summer, so temperatures may get warm, but are rarely hot. These continental regions have extreme annual temperature ranges. The boreal, coniferous forests found in the subpolar climate are called taiga and have small, hardy, and widely spaced trees. Taiga vast forests stretch across Eurasia and North America.

Polar Climates (Group E)

Polar climates are found across the continents that border the Arctic Ocean, Greenland, and Antarctica. Broadly speaking, these climates tend to have the following characteristics:

Polar Climates


The polar tundra climate is continental, with severe winters. Temperatures are so cold that a layer of permanently frozen ground, called permafrost forms below the surface. This frozen layer can extend hundreds of meters thick. The average temperature of the warmest months is above freezing, so summer temperatures defrost the uppermost portion of the permafrost. In winter, the permafrost prevents water from draining downward. In summer, the ground is swampy. Although the precipitation is low enough in many places to qualify as a desert, evaporation rates are also low, so the landscape receives more usable water than a desert.

Because of the lack of ice-free land near the South Pole, there is very little tundra in the Southern Hemisphere. The only plants that can survive the harsh winters and wet summers are small ground-hugging plants like mosses, lichens, small shrubs, and scattered small trees that make up the tundra.


Ice caps are found mostly on Greenland and Antarctica, about 9 percent of the Earth’s land area. Ice caps may be thousands of meters thick. Icecap areas have extremely low average annual temperatures, around -29 degrees Celsius (-20 degrees Farenheight ) at Eismitte, Greenland. Precipitation is low because the air is too cold to hold much moisture. Snow occasionally falls in the summer. The video below and related article from NASA highlights how the sea ice wintertime extent was the seventh-lowest ever in 2019.

Highland Climates (Group H)

When climate conditions in a small area are different from those of the surroundings, the climate of the small area is called highland or microclimates. The microclimate of a valley may be cool relative to its surroundings since cold air sinks. The ground surface may be hotter or colder than the air a few feet above it, because rock and soil gain and lose heat readily. Different sides of a mountain will have different microclimates. In the Northern Hemisphere, a south-facing slope receives more solar energy than a north-facing slope, so each side supports different amounts and types of vegetation.

Altitude mimics latitude in climate zones. Climates and biomes typical of higher latitudes may be found in other areas of the world at high altitudes.

Chapter 6 Global Climate Change for print only


6.1 Climate Change in Earth History

For the past two centuries, the climate has been relatively stable. People placed their farms and cities in locations that were in a favorable climate without thinking that the climate could change. However, the climate has changed throughout Earth history, and a stable climate is not the norm. In recent years, Earth’s climate has begun to change again. Most of this change is warming because of human activities that release greenhouse gases into the atmosphere. The effects of warming are already being seen and will become more extreme as temperature rise.

Climate has changed throughout Earth history. Much of the time Earth’s climate was hotter and more humid than it is today, but climate has also been colder, as when glaciers covered much more of the planet. The most recent ice ages were in the Pleistocene Epoch, between 1.8 million and 10,000 years ago. Glaciers advanced and retreated in cycles, known as glacial and interglacial periods. With so much of the world’s water bound into the ice, sea level was about 125 meters (395 feet) lower than it is today. Many scientists think that we are now in a warm, interglacial period that has lasted about 10,000 years.

For the past 2,000 years, the climate has been relatively mild and stable when compared with much of Earth’s history. Why has climate stability been beneficial for human civilization? Stability has allowed the expansion of agriculture and the development of towns and cities.

Relatively small temperature changes can have significant effects on the global climate. The average global temperature during glacial periods was only about 5.5 degrees C (10 degrees F) less than Earth’s current average temperature. Temperatures during the interglacial periods were about 1.1 degrees C (2 degrees F) higher than today.

Since the end of the Pleistocene, the global average temperature has risen about 4 degrees C (7 degrees F). Glaciers are retreating, and sea level is rising. While climate is getting steadily warmer, there have been a few more extreme warm and cool times in the last 10,000 years. Changes in climate have had effects on human civilization. The Medieval Warm Period from 900 to 1300 A.D. allowed Vikings to colonize Greenland and Great Britain to grow wine grapes. The Little Ice Age, from the 14th to 19th centuries, the Vikings were forced out of Greenland and humans had to plant crops further south.

6.2 Short-Term Climate Changes

Short-term changes in climate are common, with the largest and most important of these is the oscillation between El Niño and La Niña conditions. This cycle is called the El Niño Southern Oscillation (ENSO). The ENSO drives changes in climate that are felt around the world about every two to seven years.

In a typical year, the trade winds blow across the Pacific Ocean near the equator from east to west (toward Asia). A low-pressure cell rises above the western equatorial Pacific. Warm water in the western Pacific Ocean and raises sea levels by a one-half meter. Along the western coast of South America, the Peru Current carries cold water northward, and then westward along the equator with the trade winds. Upwelling brings cold, nutrient-rich waters from the deep sea.

In an El Niño year, when water temperature reaches around 28 degrees C (82 degrees F), the trade winds weaken or reverse direction and blow east (toward South America). Warm water is dragged back across the Pacific Ocean and piles up off the west coast of South America. With warm, low-density water at the surface, upwelling stops. Without upwelling, nutrients are scarce, and plankton populations decline. Since plankton forms the base of the food web, fish cannot find food, and fish numbers decrease as well. All the animals that eat fish, including birds and humans, are affected by the decline in fish.

By altering atmospheric and oceanic circulation, El Niño events change global climate patterns. Some regions receive more than average rainfall, including the west coast of North and South America, the southern United States, and Western Europe. Drought occurs in other parts of South America, the western Pacific, southern and northern Africa, and southern Europe.

An El Niño cycle lasts only a few years, with normal circulation patterns resuming. Sometimes circulation patterns bounce back quickly and remarkably, called La Niña. During a La Niña year, as in a typical year, trade winds move from east to west and warm water piles up in the western Pacific Ocean. Ocean temperatures along coastal South America are colder than average (instead of warmer, as in El Niño). Cold water reaches farther into the western Pacific than usual.

Other significant oscillations are smaller and have a local, rather than global, effect. The North Atlantic Oscillation mostly alters the climate in Europe. The Mediterranean also goes through cycles, varying between being dry at some times, and warm and wet at others.

6.3 Causes of Long-Term Climate Change

In order to have an intelligent conversation about the current warming of the planet, one must have a strong understanding of the natural causes, processes, and cycles of naturally occurring climate change. These natural processes and cycles are imputed into extremely complex climate models to analyze past, present, and future climate trends and patterns.


As noted in the chapter on Plate Tectonics, tectonic plates are moving around the earth’s surface because of convection within the mantle. This is the driving force of mountain building, earthquakes, and volcanoes around the planet. But the movement of tectonic plates can also alter regional and global climates. Over millions of years as seas open and close, ocean currents may distribute heat differently across the planet. For example, when all the continents are joined into one supercontinent (such as Pangaea), nearly all location experience a continental climate. When the continents separate, heat is more evenly distributed.

Tectonic plate movement.

Plate tectonic movements may help start an ice age. When continents are located near the poles, ice can accumulate, which may increase albedo and lower global temperature. Low enough temperatures may start a global ice age. A recent scientific study by scientists at MIT in 2019, titled Arc-continent collisions in the tropics set Earth’s climate state, suggests that the last three major ice ages occurred because of plate tectonic activity near the equator.

Tectonic plate motions can trigger volcanic eruptions, which release dust and carbon dioxide into the atmosphere. Ordinary eruptions, even large ones, have only a short-term effect on weather. Massive eruptions of the fluid lavas that create lava plateaus release much more gas and dust and can change the climate for many years. This type of eruption is exceedingly rare; none has occurred since humans have lived on Earth.

Plate tectonics and sea floor spreading.


The most extreme climate of recent Earth history was the Pleistocene. Scientists attribute a series of ice ages to variation in the Earth’s position relative to the Sun, known as Milankovitch cycles. The Earth goes through regular variations in its position relative to the Sun:

The shape of the Earth’s orbit changes slightly as it goes around the Sun, called eccentricity. The orbit varies from more circular to more elliptical in a cycle lasting between 90,000 and 100,000 years. When the orbit is more elliptical, there is a more significant difference in solar radiation between winter and summer.

Circular Eccentricity
Elliptical Eccentricity

The Earth wobbles on its axis of rotation, called precession. At one extreme of this 27,000-year cycle, the Northern Hemisphere points toward the Sun when the Earth is closest to the Sun. Summers are much warmer, and winters are much colder than now. At the opposite extreme, the Northern Hemisphere points toward the Sun when it is farthest from the Sun, resulting in cool summers and warmer winters.


The planet’s tilt on its axis varies between 22.1 degrees and 24.5 degrees, called obliquity. Seasons are caused by the tilt of Earth’s axis of rotation, which is at a 23.5o angle now. When the tilt angle is smaller, summers and winters differ less in temperature. This cycle lasts 41,000 years.


When these three variations are charted out, a climate pattern of about 100,000 years emerges. Ice ages correspond closely with Milankovitch cycles. Since glaciers can form only over land, ice ages only occur when landmasses cover the polar regions. Therefore, Milankovitch cycles are also connected to plate tectonics.


The amount of energy the Sun radiates is relatively constant over geologic time, but slightly fluctuates over the decades. Part of this fluctuation occurs because of sunspots, magnetic storms on the Sun’s surface that increase and decrease over an 11-year cycle.

The natural cycle of sunspots over the past few hundred years.

When the number of sunspots is high, solar radiation is also relatively high. However, the entire variation in solar radiation is tiny relative to the total amount of solar radiation that there is an 11-year cycle in climate variability. The Little Ice Age corresponded to a time when there were no sunspots on the Sun.



Climatic data from ice core drillings, rings within coral reefs and trees, ocean and lake sediments, and other sources indicate that when greenhouse gasses increase in the atmosphere, global temperatures rise. When greenhouse gasses decrease in the atmosphere, global temperatures fall. In 1958, the National Oceanic and Atmospheric Administration (NOAA) began measuring carbon dioxide levels in real time. What direct measurements of carbon dioxide in the atmosphere indicate is that every year, the concentration of the gas increases globally every six months and decreases six months later. This has mostly to do with the continents in the northern hemisphere, where the majority of the continents and trees are located. During the warmer months, the trees in the northern hemisphere begin photosynthesizing by taking carbon dioxide out of the atmosphere and use sunlight to create chlorophyll. This causes global greenhouse gases to decrease for six months. When the northern hemisphere experiences fall and winter, the trees stop photosynthesizing and become dormant, causing global greenhouse gases to increase. However, even though carbon dioxide levels increase and decrease every year, the global trend is that carbon dioxide levels are growing every year. Current measurements from NASA indicate that carbon dioxide levels are at 411 ppm, the highest the earth has seen in nearly a million years.

Direct measurements of carbon dioxide by NOAA.

Recently, NASA has created ultra-high-resolution computer models, giving scientists a stunning new look at how carbon dioxide in the atmosphere travels around the globe.

Greenhouse gas levels have varied throughout Earth history. For example, carbon dioxide has been present at concentrations less than 200 parts per million (ppm) and more than 5,000 ppm. However, for at least 650,000 years, carbon dioxide has never risen above 300 ppm, during either glacial or interglacial periods. Natural processes add (volcanic eruptions and the decay or burning of organic matter) and remove absorption by plants, animal tissue, and the ocean) carbon dioxide from the atmosphere. When plants are turned into fossil fuels, the carbon dioxide in their tissue is stored with them. So carbon dioxide is removed from the atmosphere.

This graph from NASA, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution.

Fossil fuel use has skyrocketed in the past few decades more people want more cars and industrial products, releasing vast quantities of carbon dioxide into the atmosphere. Burning tropical rainforests, to clear land for agriculture, a practice called slash-and-burn agriculture, also increases atmospheric carbon dioxide. By cutting down trees, they can no longer remove carbon dioxide from the atmosphere. Burning the trees releases all the carbon dioxide stored in the trees into the atmosphere.

There is now nearly 40 percent more carbon dioxide in the atmosphere than there was 200 years ago, before the Industrial Revolution. About 65 percent of that increase has occurred since the first carbon dioxide measurements were made on Mauna Loa Volcano, Hawaii, in 1958. Carbon dioxide is the most important greenhouse gas that human activities affect because it is so abundant. However, other greenhouse gases are increasing as well. The main greenhouse gases include:

6.4 Anthropogenic Climate Change


The scientific consensus is clear, in that 97 percent of all scientists who directly study climates and climate change believe that the current warming of the planet is anthropogenic (human) in nature. And all of the scientific evidence and planetary vital signs indicate that more greenhouse gases are trapping Earth’s heat, causing average annual global temperatures to rise.  While temperatures have risen since the end of the Pleistocene, 10,000 years ago, this rate of increase has been more rapid in the past century and has risen even faster since 1990. The nine warmest years on record have all occurred since 1998, and NASA and NOAA reported in 2019 that the year 2018 was the fourth warmest ever recorded on the planet. The 2010-2020 is predicted to be the warmest decade yet, followed by 2000-2010.

The United States has long been the largest emitter of greenhouse gases, with about 20 percent of total emissions. As a result of China’s rapid economic growth, its emissions surpassed those of the United States in 2008. However, it is also important to keep in mind that the United States has only about one-fifth the population of China. What is the significance of this? The average United States citizen produces far more greenhouse gases than the average Chinese person.


Climate change can be a naturally occurring process and has created environments much warmer than today, such as the early Cretaceous period. During this time, life thrived even in regions, such as the interior of Antarctica, that is uninhabitable today.

One misconception is that the threat of climate change has to do with the absolute warmth of the Earth. That is not, in fact, the case. It is, instead, the rate of change that has scientists concerned. Living things, including humans, can quickly adapt to substantial changes in climate as long as the changes take place slowly, over many thousands of years or longer. However, adapting to changes that are taking place on timescales of decades is far more challenging. But the planet is warming at such a rate that most species, especially mammals, will struggle to adapt and literally evolve quickly enough to the coming warmer climates.

Here is a useful “thought experiment” to illustrate what sort of discussion might be happening now if, instead of the current climate, we were living under the climate conditions of the last Ice Age, and human fossil fuel emissions were pushing us out of the ice age and into conditions resembling the pre-industrial period, rather than the actual case, where we are pushing the Earth out of the pre-industrial period and into a period with conditions more like the Cretaceous.

It turns out that the natural increase in atmospheric carbon dioxide that led to the thaw after the last Ice Age was an increase from 180 parts per million (ppm) to about 280 ppm. This was a smaller increase than the present-time increase due to human activities, such as fossil fuel burning, which thus far have raised CO2 levels from the pre-industrial value of 280 ppm to a current level of over 410 ppm – a level which is increasing by 2 ppm every year. So, arguably, if the dawn of industrialization had occurred 18,000 years ago, we may very likely have sent the climate from an ice age into the modern pre-industrial state.

How long it would have taken to melt all of the ice is not precisely known, but it is conceivable it could have happened over a period as short as two centuries. The area ultimately flooded would be considerably more significant than that currently projected to flood due to the human-caused elevation of carbon dioxide that has taken place so far. Below is a video from Science Insider on what the planet would like today if all the glaciers melted.

By some measures, human interference with the climate back then, had it been possible, would have been even more disruptive than the current interference with our climate. That interference would merely be raising global mean temperatures from those of the last Ice Age to those that prevailed in modern times before industrialization. What this thought experiment tells us is that the issue is not whether some particular climate is objectively “optimal.” The issue is that human civilization, natural ecosystems, and our environment are heavily adapted to a particular climate — in our case, the current climate. Rapid departures from that climate would likely exceed the adaptive capacity that we and other living things possess, and cause significant consequent disruption in our world.

The amount of carbon dioxide levels will continue to rise in the decades to come. However, the impacts will not be evenly distributed across the planet. Some of those impacts will depend on environmental and climate factors, other impacts will be dependent on whether the countries are developed or developing. Scientists use complex computer models to predict the effects of greenhouse gas increases on climate systems globally for specific regions of the world.

If nothing is done to control greenhouse gas emissions, and they continue to increase at current rates, the surface temperature of the Earth can be expected to increase between 0.5 degrees C and 2.0 degrees C (0.9 degrees F and 3.6 degrees F) by 2050 and between 2 degrees and 4.5 degrees C (3.5 degrees and 8 degrees F) by 2100, with carbon dioxide levels over 800 parts per million (ppm). On the other hand, if severe limits on carbon dioxide emissions begin soon, temperatures could rise less than 1.1 degrees C (2 degrees F) by 2100.

Whatever the temperature increase, it will not be uniform around the globe. A rise of 2.8 degrees C (5 degrees F) would result in 0.6 degrees to 1.2 degrees C (1 degree to 2 degrees F) at the equator, but up to 6.7 degrees C (12 degrees F) at the poles. So far, global warming has affected the North Pole more than the South Pole, but temperatures are still increasing at Antarctica.

Effects of Anthropogenic Climate Change

There are a variety of possible and likely effects of climate change on human and natural environments. NASA has tried to list some of those potential effects and can be found here. NASA also has a website called the Climate Time Machine, to help visualize Earth’s key climate indicators and how they are changing over time.

Human Impacts and Migration

Species Mating and Migration

The timing of events for species is changing. Mating and migrations take place earlier in the spring months, and species that are more mobile are migrating uphill. Some regions that were already marginal for agriculture are no longer farmable because they have become too warm or dry.

Melting Snowpacks and Glaciers

Decreased snow packs, shrinking glaciers, and the earlier arrival of spring will all lessen the amount of water available in some regions of the world, including the western United States and much of Asia. Ice will continue to melt, and sea level is predicted to rise 18 to 97 cm (7 to 38 inches) by 2100. An increase this large will gradually flood coastal regions where about one-third of the world’s population lives, forcing billions of people to move inland.

Glaciers are melting, and vegetation zones are moving uphill. If fossil fuel use exploded in the 1950s, why do these changes begin early in the animation? Does this mean that the climate change we are seeing is caused by natural processes and not by fossil fuel use?

Oceans and Rising Sea Levels

As greenhouse gases increase, changes will be more extreme. Oceans will become slightly more acidic, making it more difficult for creatures with carbonate shells to grow, and that includes coral reefs. A study monitoring ocean acidity in the Pacific Northwest found ocean acidity increasing ten times faster than expected and 10 percent to 20 percent of shellfish (mussels) being replaced by acid-tolerant algae.

Plant and animal species seeking cooler temperatures will need to move poleward 100 to 150 km (60 to 90 miles) or upward 150 m (500 feet) for each 1.0 degrees C (8 degrees F) rise in global temperature. There will be a tremendous loss of biodiversity because forest species cannot migrate that rapidly. Biologists have already documented the extinction of high-altitude species that have nowhere higher to go.

One may notice that the numerical predictions above contain wide ranges. Sea level, for example, is expected to rise somewhere between 18 and 97 centimeters by 2100. The reason for this uncertainty is in part because scientists cannot predict precisely how the Earth will respond to increased levels of greenhouses gases. How quickly greenhouse gases continue to build up in the atmosphere depends in part on the choices we make.

Extreme Weather

Weather will become more extreme with heat waves and droughts. Some modelers predict that the Midwestern United States will become too dry to support agriculture and that Canada will become the new breadbasket. In all, about 10% to 50% of current cropland worldwide may become unusable if CO2 doubles. There are global monitoring systems to help monitor potential droughts that could turn into famines if they occur in politically and socially unstable regions of the world and if appropriate action is not taken in time. One example is the Famine Early Warning System Network (FEWS NET), which is a network of social and environmental scientists using geospatial technology to monitor these situations. However, even with proper monitoring, if nations do not act, catastrophes can occur like in Somalia from 2010-2012.

Although scientists do not all agree, hurricanes are likely to become more severe and possibly more frequent. Tropical and subtropical insects will expand their ranges, resulting in the spread of tropical diseases such as malaria, encephalitis, yellow fever, and dengue fever.

An important question people ask is this: Are the increases in global temperature natural? In other words, can natural variations in temperature account for the increase in temperature that we see? The scientific data shows no, natural variations cannot explain the dramatic increase in global temperatures. Changes in the Sun’s irradiance, El Niño and La Niña cycles, natural changes in greenhouse gas, plate tectonics, and the Milankovitch Cycles cannot account for the increase in temperature that has already happened in the past decades.

In December 2013 and April 2014, the Intergovernmental Panel on Climate Change (IPCC) released a series of damaging reports on not only the current scientific knowledge of climate change but also on the vulnerability and impacts to humans and ecosystems. Below are two videos detailing the physical science of climate change and the risks and impacts to the planet.

6.5 Changing the Climate Change Narrative

However, it is essential to get a data-driven understanding of climate change. Along with the IPCC, other organizations like the United Nations Environmental Programme (UNEP), World Health Organizations, World Meteorological Organization (WMO), National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Environmental Protection Agency (EPA).

Chapter 7 Population and Migration for print only

Understanding how the human population is organized geographically helps us make sense of cultural patterns, the political organization of space, food production issues, economic development concerns, natural resource use and decisions, and urban systems. Additionally, themes of location, space, place, the scale of analysis, and pattern can be emphasized when studying fundamental population issues such as crude birth rates, crude death rates, total fertility rate, infant mortality rates, doubling time, and natural increase.

Explanations of why the population is growing or declining in some places are based on patterns and trends in fertility, demographic mortality, and migration. Analyses of refugee flows, immigration, and internal migration help us understand the connections between population phenomena. For example, environmental degradation and natural hazards may prompt population redistribution at various scales, which in turn creates new pressures on the environment, culture, and political institutions.

This chapter will analyze population trends across space and time as ways to consider models of population growth and decline, including Malthusian demographic transition, and the epidemiological (mortality) transition model.

Essential understanding and Learning Objectives

Population Growth

Geographers study where and why people live in particular locations. Neither people nor resources are distributed uniformly across Earth. In regards to population growth, geographers emphasize three elements: the population size; the rate of increase of world population; the unequal distribution of population growth. Geographers seek to explain why these patterns exist.

The subject of overpopulation can be highly divisive given the deep personal views that many hold on abortion. This course emphasizes a geographic perspective on population growth as a relative concept. Population, from a geography perspective, should be viewed in the context of the availability of resources. Human-environment interaction and overpopulation can be discussed in the contexts of carrying capacity, as well as the relationship between people and resources.

The study of population has never been more important than it is today.  There are over 7 billion people on the planet, but the majority of this growth has occurred in the last 100 years, mostly in developing nations. Humans do not live uniformly around the planet, but rather in clusters because of earth’s physical geography. Environments that are too dry, wet, cold, or mountainous create a variety of limiting factors to humans. Two-thirds of the world’s population is located within four major clusters: East Asia (China), South Asia (India and Indonesia), Southeast Asia, and Europe, with the majority in East and South Asia.

Demographers, scientists that study population issues, and other scientists say there is more to the story than simple population growth.  Ecologists believe that humans have out-grown the Earth’s carrying capacity, which is a scientific way of saying that the planet can no longer sustain or support human activity.  Simply put, there is just not enough of the world’s resources to give every human a standard of living expected by most Americans.  If fact, if all 7 billion people on the planet lived the average American lifestyle, it would require over three Earth’s. This raises several issues: that the planet cannot sustain a population of 7 billion, though we are expected to reach 9 billion by 2100, and that the planet cannot sustain Western lifestyles for the entire planet.

7.1: Where Humans Live

Humans only occupy five percent of the Earth’s surface because oceans, deserts, rainforests, and glaciers cover much of the planet. The term for areas where humans permanently settle is called ecumene. Population growth and technology dramatically increase the ecumene of humans, which affects the earth’s surface and natural systems.

Issues and concerns of growing human populations have less to do with space and more to do with habitual locations and access to natural resources. All 7.57 billion people on the planet could live within an area the size of Los Angeles, California, but that is not desirable, sanitary, or sustainable. The reality is that humans cannot live in many parts of the world due to moisture, temperature, mountains, or growing season issues. Twenty percent of the world is too dry to support humans. This mostly has to do with large-scale high-pressure systems around 30 degrees north and south of the equator where constant sunny conditions have created some of the world’s largest deserts. Some of these include the Sahara, Arabian Peninsula, Thar, Takla Makan, and Gobi deserts. Most deserts do not provide enough moisture to support agriculture for large populations. Those who do live in these regions tend to raise animals and are considered nomads.

Regions that receive too much moisture also cause problems for human settlement. These are tropical rainforest regions located between the Tropic of Cancer (23.5 degrees North) and the Tropic of Capricorn (23.5 degrees South). The problem with these regions of the world has to do with the soil erosion due to high precipitation. High levels of precipitation greatly hinder agricultural production because nutrients in the soil are quickly washed away. This is partly why slash-and-burn agriculture occurs in these regions. Locals will burn part of the forest to put nutrients back into the ground. This only works for a short period because the precipitation washes away nutrients within a few years, so farmers move on to other parts of the forest with their slash-and-burn practices.

Additionally, regions that are too cold pose problems for large population clusters and food production. The cold polar regions have a short growing season, snow cover, permanently frozen land called permafrost, or high-pressure systems near the poles that limit the amount of moisture an area receives. Thus, cold polar regions are not only limited by temperature, but they are also limited by lack of moisture despite access to snow, ice, and glaciers. Mountainous and highland regions lack population clusters for similar reasons: steep slopes, snow and ice cover, and short growing seasons.

Because of these environmental factors, two-thirds of the world’s population is clustered into four geographic regions: Europe, East Asia, South Asia, and Southeast Asia. In Europe, three-fourths of people living there live in cities. In East Asia, most of the people live near coastal regions by the Pacific Ocean or near major river systems. Over half of the people in East Asia live in rural areas and are likely to be farmers. Similar to East Asia, people living in South Asia live near major river systems such as the Ganges and Indus rivers in order to have access to water for farming. Southeast Asia is quite different from the other three regions because most of the people live on islands within the Pacific and Indian oceans. But similar to East Asia and South Asia, the majority of people living in Southeast Asia live in rural areas and are likely to be farmers.

7.2: Global Population Trends

Arithmetic Density Map
Arithmetic Density Map

Agricultural density refers to the number of farmers valuable to arable land. A high agricultural density suggests that the available agricultural land used for farming and the farmers who are capable of producing and harvesting food is reaching its limit for that region. If the demand for food continues or rises, the risk is that there will not be enough arable land to feed their people. In contrast, an area with a low agricultural density has a higher potential for agricultural production. Economically, a low agricultural density would be favorable for future growth. Developed countries tend to have a much lower agricultural density because of technology. When geographers study and compare physiological and agricultural densities, they can analyze and determine the relationship between a country’s population and resources.


Population pyramid of China in 2016.
Population pyramid of China 2016.

A useful and critical tool used by scientists that focus on demographics, this included geographers, demographers, and social scientists, is a population profile called a population pyramid. A population pyramid visually demonstrates a particular region’s demographic structure about males and females and is often expressed in numbers or percentages. The following are some characteristics of population profiles:

  • A bell-shaped graph will indicate that a country has experienced high population growth in the early past but is experiencing a slow decrease.
  • Pyramids with a large base indicate countries with high population growth.
  • As a country’s population boom begins to age, a strange profile shape can develop with a wider top and a narrower base.
  • Populations that have stabilized have profiles where the majority of the pyramid is uniform in shape and gets smaller towards the top.
  • When a country has a large immigrant population, specifically “guest workers” than usually tend to be men, the male side of the graph will be dramatically wider than the women side of the graph.

If a country has experienced war, a catastrophic disaster, or a genocide that eliminates an entire generation, that generation will have a smaller number or percent than the generations before or after. For example, a major war may cause a reduction in populations in their mid-20s and 30s, and potentially a greater loss of males, which would appear on the profile graph.

Demographic Transition Model (DTM) pyramids.
Demographic Transition Model (DTM) pyramids.


Before we look at the model used to analyze how populations change, it is essential to look at key factors that influence the structure of a population. A region’s population will grow as long as their crude birth rates are greater than their crude death rates. A crude birth rate (CBR) is the total number of live births for every 1,000 people in a given year. So a crude birth rate of 10 would mean ten babies are born every year for every 1,000 people in that region. Crude death rates (CDR) are the total number of deaths per 1,000 people in a given year.


Crude Death Rates Map
Crude Death Rates Map

When CBRs are compared to CDRs, a region’s natural increase rate can be determined. A natural increase rate (NIR) is the percent a population will grow per year, excluding annual migration. Usually, a NIR of 2.1 is required to maintain or stabilize a region’s population. Any more than that and the population will grow, any less than a NIR of 2.1 causes population contraction. The reason why the NIR percent is 2.1 and not 2.0 for stability is because not every human will pair up and have a child because of genetics, choice, or death before childbearing years. Once we know the NIR, we can determine doubling time. Doubling time is the how many years would it take for a defined population to double in size, assuming that NIR stays the same over time. Over 95 percent of the world’s natural increase is occurring in developing countries. Subsaharan Africa and parts of Southwest Asia have NIR over 2.0, leading to large population growth, whereas regions in Europe have NIR near zero causing the population to decline. Currently, about 75 million people are added to the world’s global population every year.

The total fertility rate (TFR) is the average number of children a woman would be expected to have during the childbearing years (between 15-49 years old). The global average for TFRs is about 2.5, but in developing countries, it is as high as 5.0 or higher, and in more developed countries it is as low as 2.0 or less. The total fertility rate is a direct expression of a nation’s health care system because it reflects a population’s access to doctors, nurses, hospitals, and medicine.

The next important term to understand is the infant mortality rate (IMR). The IMR is determined by calculating how many children die before the age of 1 per 1,000 live births annually. The highest IMRs are in developing countries where rates can be as high as 80 or more. Conversely, in regions like Europe, it is as low as 5 per 1,000 live births annually.

Life expectancy at birth is an average of how many years a newborn is expected to live, assuming that mortality rates stay consistent. In more developed countries, the average life expectancy is over 80 years old, and in developing countries, it is only around 40 years. When we compare CBRs, CDRs, and TFRs, we find that the world has a large population of youth with the largest percent in developing countries. This causes high stress on the education systems and to some extent the health care systems within more impoverished countries.

However, more developed countries tend to have older demographics, which tends to cause stresses on the health care and social safety nets of those countries. The dependency ratio discussed later in this chapter, is used to understand these stresses and is the number of people who are too young or too old to work compared to the number of people who are in their “productive years.” The larger the ratio, the higher the economic stress on those nations.

7.4 Demographic Theories

Geographers and other social scientists have long looked at population issues as central to understanding human interactions. Below we will look at four theories about population that inform sociological thought: Malthusian, zero population growth, cornucopian, and demographic transition theories.

Demographic Transition Model

Whether you believe that we are headed for environmental disaster and the end of human existence as we know it, or you think people will always adapt to changing circumstances, we can see clear patterns in population growth. Societies develop along a predictable continuum as they evolve from unindustrialized to postindustrial. Demographic transition theory (Caldwell and Caldwell 2006) suggests that future population growth will develop along a predictable four-stage model.

Human geographers have determined that all nations go through a four-stage process called the Demographic Transition Model (DTM). The DTM’s function is to demonstrate the natural sequence of population change over time-based on development and modernization. This can help geographers, and other scientists examine the causes and consequences of fertility, mortality, and natural increase rates. Though controversial, the DTM has been used as the benchmark for forecasting human population growth regionally and globally.



Humans have lived in the first stage of the DTM for most of our existence. In this first stage, CBRs and CDRs fluctuated greatly regionally, globally, and over time because of living conditions, food output, environmental conditions, war, and disease. Ultimately, the natural increase of the world was stable because CBRs and CDRs were about equal. However, around 8,000 BC, the world’s population began to grow dramatically due to the agricultural revolution. During this time, humans learn to domesticate plants and animals for personal use and became less reliant on hunting and gathering for sustenance. This allowed for more stable food production and allowed village populations to grow. War and disease prevented population growth from occurring on a global scale.


Around the mid-1700s, global populations began to grow ten times faster than in the past because of the Industrial Revolution. The Industrial Revolution brought with it a variety of technological improvements in agricultural production and food supply. Increased wealth in Europe, and later North America, because the Industrial Revolution meant that more money and resources could be devoted to medicine, medical technology, water sanitation, and personal hygiene. Sewer systems were installed in cities; thus public health improved. All of this dramatically caused CDRs to drop around the world. At first, CBRs stayed high as CDRs dropped, this caused populations to increase in Europe and North America. Over time, this would change.

Africa, Asia, and Latin America moved into Stage 2 of the demographic transition model 200 years later for different reasons than their European and North American counterparts. The medicine created in Europe and North America was brought into these developing nations creating what is now called the medical revolution. This revolution or diffusion of medicine to this region caused death rates to drop quickly. While the medical revolution reduced death rates, it did not bring with it the wealth and improved living conditions, and development that the Industrial Revolution created. Global population growth is most significant in the regions that are still in Stage 2.


Today, Europe and North America have moved to Stage 3 of the demographic transition model. A nation moves from Stage 2 to Stage 3 when CBRs begin to drop while CDRs remain low or even continue to fall. It should be noted that the natural rate of increase in nations within Stage 3 is moderate because CBRs are somewhat higher than CDRs. The United States, Canada, and nations in Europe entered this stage in the early 20th Century. Latin American nations entered this stage later in the century.

Advances in technology and medicine cause decrease in IMR and overall CDR during Stage 2. Social and economic changes bring about a decrease in CBR during Stage 3. Countries that begin to acquire wealth tend to have fewer children as they move away from rural-based development structures toward urban-based structures because more children survive childhood and the need for large families for agricultural work decreases. Additionally, women gained more legal rights and chose to enter the workforce, own property, and have fewer children as nations move into Stage 3.


A country enters Stage 4 of the demographic transition model when CBRs equal to or become less than CDRs. When CBRs are equal to CDRs, a nation will experience zero population growth (ZPG). This occurs in many countries where girls do not live as long before they reach their childbearing years due to gender inequality.

A country in the first two stages of the transition model will have a broad base of young people and a smaller proportion of older people. A country in Stage 4 will have a much smaller base of young people (fewer children), but a much larger population of elderly (decreased CDR). A country with a large youth population is more likely to be rural with high birthrates and possibly high death rates; helping geographers analyze a nation’s health care system. Moreover, a country in Stage 4 with a large elderly population will have much fewer young people supporting the economy. These two examples represent the dependency ratio, mentioned earlier in this chapter. This ratio is the number of people, young and old, who are dependent on the working force.

Human geographers like to focus on the following demographic groups: 0-14 years old, 15-64 years old, and 65 and older. Individuals who are 0-14 and over 65 are considered dependents (though this is changing in older generations). One-third of all young people live in developing nations. Moreover, this places great strain on those nations’ infrastructure such as schools, hospitals, and day-care. Older individuals in more developed nations (MDL) benefit from health care services, but require more help and resources from the government and economy.

Another ratio geographers look at is the number of males compared to females, called the sex ratio.  Globally, more males are born than females, but males have a higher death rate than females.  However, understanding a country’s sex ratio and their dependency ratio helps human geographers analyze fertility rates and natural increase.

As noted earlier, population growth has increased dramatically in the last century. No country is still in Stage 1, and very few have moved into Stage 4. The majority of the world is either in Stage 2 or 3, which both have higher CBRs than CDRs; creating a human population over 7.5 billion today.


Many demographers believe a new stage in the DTM should be added to address issues starting to develop in countries within Europe and Japan. In this final stage, CBR would be extremely low and an increasing CDR. This would cause the area’s NIR to potentially become negative, leading to declining population growth. This may create an enormous strain on the social safety net programs of a country as is tries to support older citizens who are no longer working and contributing to the economy.

Currently, most of Europe has entered Stage 4. The United States would be approaching this stage if it were not for migration into the country. The first country that would enter Stage 5 would be Japan.

In summary, the demographic transition model is a model that helps human geographers understand and predict the demographics of individual nations. In Stage 1, CBR and CDR are very high and thus produce a low natural increase. In Stage 2, a nation’s CBR stays relatively high, but the CDR drops dramatically, producing the highest growth in population. In Stage 3, CDR stays low; however, changes in social customs and economic conditions. Finally, nations in Stage 4 have nearly equal CBR and CDR (sometimes higher CDR), creating a drop in natural increase.

Malthusian Theory

Overpopulation occurs when the number of people in an area exceeds the carrying capacity of the environment to support life at a decent standard of living. Thomas Malthus (1766–1834) was an English clergyman who made dire predictions about earth’s ability to sustain its growing population. According to Malthusian theory, three factors would control human population that exceeded the earth’s carrying capacity, or how many people can live in a given area considering the amount of available resources. Malthus identified these factors as war, famine, and disease (Malthus 1798). He termed them “positive checks” because they increase mortality rates, thus keeping the population in check. They are countered by “preventive checks,” which also control the population but by reducing fertility rates; preventive checks include birth control and celibacy. Thinking practically, Malthus saw that people could produce only so much food in a given year, yet the population was increasing at an exponential rate. Eventually, he thought people would run out of food and begin to starve. They would go to war over increasingly scarce resources and reduce the population to a manageable level, and then the cycle would begin anew.

Of course, this has not exactly happened. The human population has continued to grow long past Malthus’s predictions. There are three reasons sociologists believe we are continuing to expand the population of our planet. First, technological increases in food production have increased both the amount and quality of calories we can produce per person. Second, human ingenuity has developed new medicine to curtail death from disease. Finally, the development and widespread use of contraception and other forms of family planning have decreased the speed at which our population increases.

Some still believe Malthus was correct and that ample resources to support the earth’s population will soon run out. While new technologies have helped to increase food production, there are not enough emerging technologies to handle supply and demand. Adding to the problem is the fact that many insects have developed a resistance to pesticides. These problems have caused a slowdown and leveling off of food production in many regions of the world. Without breakthroughs in safe and sustainable food production, food supply will not keep up with population growth.

Others believe that population growth is not a bad thing. A large population could stimulate economic growth, and therefore, production of food. Population growth could generate more customers and more ideas for improving technology. Additionally, some maintain that no cause-and-effect relationship exists between population growth and economic development. They argue that poverty, hunger, and other social welfare problems associated with a lack of economic development, famines, and war are a result of unjust social and economic institutions, not population growth.

Zero Population Growth

A neo-Malthusian researcher named Paul Ehrlich brought Malthus’s predictions into the twentieth century. However, according to Ehrlich, it is the environment, not specifically the food supply, that will play a crucial role in the continued health of planet’s population (Ehrlich 1968). Ehrlich’s ideas suggest that the human population is moving rapidly toward complete environmental collapse, as privileged people use up or pollute a number of environmental resources such as water and air. He advocated for a goal of zero population growth (ZPG), in which the number of people entering a population through birth or immigration is equal to the number of people leaving it via death or emigration. While support for this concept is mixed, it is still considered a possible solution to global overpopulation.

Epidemiological Transition Model

One problem with the Demographic Transition Model is that it poorly considers health threats to populations within each stage. The epidemiological transition addresses precise health threats to countries in demographic transition. Said another way, it focuses on specific causes of death within each stage of the DTM. Epidemiology is a branch of health science that analyzes the causes, distribution, and control of disease in a population. Researchers in epidemiology have a strong background in geography and spatial science.


Infectious diseases and parasites are the greater killers of humans on the planet. The greatest epidemic in human history was the Black Plague, which killed nearly a half of Europe’s population between 1347 and 1350. It is believed that 25 million people died in those three years.


A pandemic is an epidemic of infectious disease that has spread across a large region, affecting high proportions of the population. Diseases like cholera and malaria greatly impact countries in Stage 2 of the DTM because of overcrowding, contaminated water sources, and lack of a strong health care infrastructure.


The causes of death for countries in Stage 3 of the DTM tend to be more from chronic disorders related to age and less from infectious diseases. Rather than dying from cholera, malaria, AIDS, or Ebola, populations in Stage 3 die from cancer or cardiovascular diseases such as heart attacks. The reason why countries in Stage 2 die less from degenerative diseases is that their life expectancy is much shorter.


Though degenerative diseases still exist for countries in this stage, medical advances and technology prolong the life expectancy further than countries in the third stage. Delayed degenerative diseases are reduced further as society makes lifestyle changes in health regarding diet, tobacco and alcohol consumption, and exercise.


As noted earlier, the United States Census Bureau estimates that the world population is roughly 7.57 billion people. Governments and other entities can dramatically influence population change as a way to increase or decrease population growth in a particular country. For example, some countries take dramatic steps to reduce their population. China’s One-Child Policy dictated that each family (husband and wife) could legally have only one child. Families that followed this policy were often given more money by the government or better housing. If a family illegally had another child, the family would be fined heavily. Children born illegally cannot attend school and have a difficult time finding jobs, getting government licenses, or even getting married. Some have reported that the government would force abortions on families with more than one child. One of the significant consequences of this policy was a dramatic increase in abortions and infanticides, especially of females. Female infanticide is linked directly to a global cultural trend that privileges males over females—baby boys are desired, especially if the family is only allowed, one child. This specific focus on eliminating women is called gendercide. Half the Sky, written by Nicholas Kristof and Sheryl WuDunn, documents global gendercide and what is being done to combat this problem.

After the two great world wars, the United Nations Population Commission and the International Planned Parenthood Federation began to advocate for more global population control. Many groups who advocate for population control focus on:

  • Changing cultural attitudes that keep population rates high (or low)
  • Providing contraception to developing countries
  • Helping countries study population trends by improving census counts
  • Empowering women and emphasizing gender equality

It is believed that worldwide, over 60 percent of women between ages 15-49 use some form of contraception, though this varies regionally. In the United States, contraception use is at nearly 75 percent, whereas in Africa it is around 30 percent. The consensus today is that the focus on population planning should be on gender equality and improving the social status of women around the world. This is the focus of the International Conference on Population and Development. Religious organizations are also concerned with population growth; however, they focus on contraception issues and not strictly population growth. Some religions and political entities find contraception use immoral, which has influenced some governments to make access to them and use of them illegal.

7.6: Global Migration

Migration, a form of relocation diffusion, is defined as the permeant movement of people to a new location. Emigration is a form of migration from a particular location. Immigration is the migration to a new location. The numerical difference between emigration and immigration is called net migration.

Though geography does not have a comprehensive theory on migration, nineteenth-century geographer, E. G. Ravenstein created a few migration laws that can help us understand migration. These rules focus on the distance people migrate, the reasons why they relocate, and the characteristics of migrants.


Most people that migrate travel only a short distance from their original destination and usually within their country, usually due to economic factors. This is called internal migration. Internal migration can be divided up even further into interregional migration (the permanent movement from one region of a country to another region) and intraregional migration (the permanent movement within a single region of a country). The other type of migration is called international migration, which is the movement from one country to another. Roughly 10 percent of the people in the world are international migrants, meaning they currently live in a country they were not born in.

Some people are allowed to voluntarily migrate based on individual choice. At other times, a people relocate against their will, called forced migration. Ultimately, the distance people migrate is depends on economic, gender, family status, and cultural factors. For example, long-distance migration tends to involve males looking for employment and traveling by themselves rather than risk taking their families.

Migration is very dynamic around the world with peaks in different regions at different times. There are several reasons why people migrate to someplace or from someplace. Migration transition is the change in migration patterns within a society caused by industrialization, population growth, and other social and economic changes that also produce the demographic transition. A critical factor in all forms of migration is mobility, the ability to move either permanently or temporarily. Most international migrants come from countries in Stage 2 of the Demographic Transition Model, whereas internal migrants tend to originate from countries in Stage 3 or 4 of demographic transition.

There has been a dramatic increase in immigration into the United States from Latin America, Africa, and the Middle East. Some from these regions migrate to the U.S. out of economic necessity. We hear quite a lot about guest workers in the United States. These are individuals who migrate temporarily to take up jobs in other countries. Others migrate to escape conflicts such as the civil wars in Somalia, Sudan, and Ethiopia. Genocides in Rwanda (1994) and more recently Darfur, Sudan have forced internal and international migration. The wars in Afghanistan and Iraq have also forced migration from these regions. Washington Post reporter Sudarsan Raghavan reported on February 4, 2007, that the U.N. High Commission for Refugees estimates that over 2 million Iraqis (nearly 8 percent of the pre-war population) have been forced to migrate to nearby nations of Jordan, Syria, and Lebanon.


There are several reasons why people migrate, and these are called push and pull factors, and they usually occur because of an area’s political, economic, cultural, or environmental conditions. Push factors are events and conditions that compel an individual to move from a location. Pull factors are conditions that influence migrants to move to a particular location. The number one reason why people migrate is for economic reasons. This is because people either get “pushed” away from where they live due to a lack of employment opportunities or pulled because somewhere else either offer more jobs/higher paying jobs.

Cultural and political push factors usually involve slavery, political instability, ethnic cleansing, famine, or war. People who choose to flee or are forced to flee as a result of these problems are often called refugees. The United States Committee for Refugees classifies a refugee as someone who has been forced from their homes and cannot return because of their religion, race, nationality, or political opinion. In 2010, the United Nations High Commission for Refugees estimated that there are over 44 million people worldwide that have been forcibly displaced. The number grows to another 27 million when internally displaced persons are factored in. An internally displaced person (IDP) is someone who has been forced to migrate, but has not migrated across an international border. Some migrants are considered asylum seekers, who are people that have migrated to another country in hopes of being recognized as a refugee. Political or cultural pull factors could include people who want to live in democratic societies, gender equality, or educational or religious opportunities.

A variety of environmental push and pull factors also influence migration patterns. Environmental pull factors can include people wanting to live in particular environments. For example, many older adults like to live in southwestern states in the United States because they prefer the recreational opportunities that are provided for retired individuals. Some people want to live where snow activities are available or near an ocean.

Push factors often are related to the frequency of natural disasters such as earthquakes, tsunamis, hurricanes, or flash floods that a region could experience. Climatic push and pull factors, such as droughts, also influence migration patterns. A very recent example of this is the famine in Somalia. The main reason for environmental refugees is because of water; either too much or not enough. Sometimes people who want or need to relocate find various intervening obstacles, which are environmental or cultural features of the landscape that hinders migration.

The United States Agency for International Development (USAID) and the Famine Early Warning System track potential famines globally so that relief organizations can have a heads up and be more proactive when events occur. People who have been pushed for environmental reasons are called environmentally displaced persons (also called environmental refugees). The problem with these refugees is that they are not protected or given the same rights under the 1951 Refugee Convention. Under the convention, a refugee is a person with: “well-founded fear of being persecuted for reasons of race, religion nationality, membership of a particular social group or political opinion, who is outside the country of his nationality and is unable o, owing to such fear, is unwilling to avail himself of the protection of that country.” However, more and more people are becoming environmental refugees because of climate change, droughts, flooding from massive storm systems, water shortages, and more.


As mentioned earlier, most people relocate for economic push or pull factors. The United States, Canada, and Europe are primary locations migrants seek to relocate to for economic reasons. A struggle that many countries try to address is determining if a migrant is seeking economic opportunities or refugees fleeing governmental persecution. This distinction is important because many developed countries, including the United States, treat those two categories differently. Migrants who seek economic opportunities are less likely to be allowed into a country unless they provide a specific skill set the economy needs. If they are allowed into a country, it usually is on a temporary basis. Whereas, refugees receive special priorities with being allowed into a country and are more often than not, allowed to stay permanently.

A common practice of migrants who find work in another country will send a portion of their wages to family members back home. When migrants transfer money back to their home of origin, it is called remittance.


Ravenstein theorized that males were more likely to migrate than females, the longer the distance to relocate. The idea is that men are more likely to find employment than women. For much of human history, this was actually the case. But in the 1990s, gender patterns regarding migration began to change. Now, more women migrate to the United States than males.

Ravenstein also believed that long-distance migration occurred more with young adults, rather than children and elderly. In the United States, over 40 percent of immigrants are young adults. Children make up roughly 16 percent, and elderly make up less than 5 percent of immigration into the United States.

There is a growing concern of unaccompanied minors, between 12 to 17 years old in age, migrating to the United States. The majority of them are males, coming from Honduras and El Salvador because of gang violence.

Unauthorized Immigration

The political border between the United States and Mexico is 1,951 miles long. Currently, the United States has built various barriers along roughly one-quarter of the border. Protection of the border consists of a variety of technologies and resources including steel fences, drones, check-points, and immigration officers.

As noted earlier, the United States would be nearly the end of Stage 3 in the Demographic Transition Model if it were not for immigration. The desire to migrate to the United States continues to grow, but many cannot enter the country legally. Those who enter the country illegally, without proper documentation, are called unauthorized immigrants. The main pull factor for migrants to enter illegally is for economic reasons.

The Pew Research Center believes that as of 2013, roughly 11.3 million unauthorized immigrants currently live in the United States. The Center also determined that California and Texas have the fastest growing unauthorized immigrants. The majority of them originate from Mexico, followed by Latin America. Of the 11.3 million unauthorized immigrants, roughly 1 million are children.

Unauthorized immigrants have also given birth to roughly 4.5 million babies, which are legal U.S. citizens under current law. And finally, of the 11.3 million unauthorized immigrants, approximately 8 million are currently employed in the United States.

There are greater concerns in the United States and Europe regarding unauthorized immigration. In the United States, many Americans are growing concerned about border security. In December 2018 through January 2019, the U.S. federal government was shut down over a dispute between Congress and the President around funding the government and border security. Most Americans want stronger border security, but question how much to pay and what to invest in for that protection. Others have concerns about jobs being given to unauthorized immigrants, even though most of those jobs are not sought after by most Americans.

Interestingly enough, unauthorized immigration is controversial in Mexico as well. Most of the immigration from Mexico comes from the north of the country. But immigration from Mexico’s southern border comes from Latin American countries such as Guatemala. The people of southern Mexico are unsure of immigration from their southern border for many of the same reasons as the United States.

In Europe, immigrants come from poorer regions from the south looking for economic opportunities. Poorer countries favor allowing their citizens to migrate to Europe as a way to take stress off their low employment. Immigrants who migrate to Europe also send remittances back to their places of origin. As a way to accommodate and benefit from these migrants, many European countries use to have guest worker programs. Typically, guest workers come from developing countries and are allowed to stay and work legally, temporarily. Circular migration occurs when a migrant temporarily moves to a country to work, returns home, but returns again when work is needed again. But today in Europe, most guest worker programs have been dissolved.

Attitudes of immigrants in Europe and the United States have eroded over the years. Many blame immigrants for crime, unemployment, and stress on their social safety net and welfare programs. Ultimately, anti-immigration groups fear that immigrants will interfere with cultural traditions as migrants bring different religions, languages, foods, and habits with them. These tensions are fueling extremist groups and a recent resurgence in nationalism, racism, and bigotry in Europe and the United States.


United States created the Quota Act in 1921 and the National Origins Act in 1924, as a way to curb unrestricted immigration. These laws created a quota, a maximum limit on the number of people allowed to migrate to the United States every year. Because more migrants want to relocate to the United States than the country will allow in, the country has created the following priorities:

  • Roughly three-fourths of legal immigration into the United States is for family reunification.
  • Migrants who offer specific economic, scientific, or technological skill sets are the second largest group allowed to migrate into the country.
  • Finally, a small portion of migrants is allowed into the country through a lottery system to increase diversity from countries who have historically sent few people to the United States.

The quota system for the United States does not include refugees. Some countries have stated that because the United States allows migrants who offer important or skilled work to enter the country legally, it leads to a brain drain from the countries these migrants come from. Another aspect of immigration in the United States deals with chain migration. When skilled workers are allowed to migrate to the United States, they have the ability to bring family members into the country legally, called chain migration.

Chapter 8 Cultural Patterns and Processes for print only

Understanding the components and regional variations of cultural patterns and processes are critical to human geography. We studied the concepts of culture and cultural traits and learned how geographers assess the spatial and place dimensions of cultural groups as defined by language, religion, ethnicity, and gender, in the present as well as the past.

This module also explored cultural interaction at various scales, along with the adaptations, changes, and conflicts that may result. The geographies of language, religion, ethnicity, and gender are studied to identify and analyze the patterns and processes of cultural differences. We distinguished between languages and dialects, ethnic religions and universal religions, and folk and popular cultures, as well as between ethnic political movements. These distinctions help students understand the forces that affect the geographic patterns of each cultural characteristics.

Another significant emphasis of the module was the way culture shapes relationships between humans and the environment. We learned how culture is expressed in landscapes and how land use, in turn, represents cultural identity. Built environments enable the geographer to interpret cultural values, tastes, symbolism, and beliefs.

Learning Objectives

Concepts of culture frame the shared behaviors of a society.

  • Explain the concept of culture and identity of cultural traits.
  • Explain how geographers assess the spatial and place dimensions of cultural groups in the past and present.
  • Explain how globalization is influencing cultural interactions and change.

Culture varies by place and region.

  • Explain cultural patterns and landscapes as they vary by place and region.
  • Explain the diffusion of culture and cultural traits through time and space.
  • Compare and contrast ethnic and universalizing religions and their geographic patterns.
  • Explain how culture is expressed in landscapes and how land and resources use represents cultural identity.
  • Compare and contrast popular and folk culture and the geographic patterns associated with each.

8.1 Understanding Race and Ethnicity

Defining Race and Ethnicity

The idea of race refers to superficial physical differences that a particular society considers significant, while ethnicity describes shared culture. Moreover, the term “minority groups” describe subordinate groups, or that lack power in society regardless of skin color or country of origin. For example, in modern U.S. history, the elderly might be considered a minority group due to a diminished status that results from widespread prejudice and discrimination against them. Ten percent of nursing home staff admitted to physically abusing an older person in the past year, and 40 percent admitted to committing psychological abuse (World Health Organization 2011). In this chapter, we focus on racial and ethnic minorities.

Race, in biological terms, refers to a socially constructed way to identify humans based on physical characteristics, resulting from genetic ancestry. Shared genetic ancestry is a result of geographical isolation. Geographic isolation, since the era of colonization and even before then, has significantly decreased in most areas of the world. Less geographic isolation results in the mixing of racial groups. Thus, classifying people by their race with any accuracy is difficult.

Most biologists, geographers, and social scientists have all taken an official position rejecting the biological explanations of race. Over time, the typology of race that developed during early racial science has fallen into disuse, and the social construction of race is a more sociological way of understanding racial categories. Research in this school of thought suggests that race is not biologically identifiable and that previous racial categories were arbitrarily assigned, based on pseudoscience, and used to justify racist practices (Omi and Winant 1994; Graves 2003). When considering skin color, for example, the social construction of race perspective recognizes that the relative darkness or fairness of skin is an evolutionary adaptation to the available sunlight in different regions of the world.

Contemporary conceptions of race, therefore, which tend to be based on socioeconomic assumptions, illuminate how far removed modern understanding of race is from biological qualities. In modern society, some people who consider themselves “white” actually have more melanin (a pigment that determines skin color) in their skin than other people who identify as ”black.” In some countries, such as Brazil, class is more important than skin color in determining racial categorization. People with high levels of melanin may consider themselves “white” if they enjoy a middle-class lifestyle. On the other hand, someone with low levels of melanin might be assigned the identity of “black” if he or she has little education or money.

The social construction of race is also reflected in the way names for racial categories change with changing times. It is worth noting that race, in this sense, is also a system of labeling that provides a source of identity; specific labels fall in and out of favor during different social eras. For example, the category ”Negroid,” popular in the nineteenth century, evolved into the term “negro” by the 1960s, and then this term fell from use and was replaced with “African American.” This latter term was intended to celebrate the multiple identities that a black person might hold, but the word choice is a poor one: it lumps together a large variety of ethnic groups under an umbrella term while excluding others who could accurately be described by the label but who do not meet the spirit of the term. For example, actress Charlize Theron is a blonde-haired, blue-eyed “African American.”

PBS has created an exciting website called RACE – The Power of an Illusion that looks at whether race indeed is a biological characteristic of humans or a social construct. Take the Sorting People quiz and watch The Human Family Tree and Black in Latin America: An Island Divided to “witness” how migration and geography play a role in the complex issues surrounding race and ethnicity. Pay attention to how the racial and ethnic landscape of the island of Hispaniola impacts cultural identity and the geopolitics both within Hispaniola and beyond its shores.

Ethnicity is a term that describes shared culture – the practices, values, and beliefs of a group. This culture might include shared language, religion, and traditions, among other commonalities. Like race, the term ethnicity is difficult to describe, and its meaning has changed over time. Moreover, as with race, individuals may be identified or self-identify with ethnicities in complex, even contradictory, ways. For example, ethnic groups such as Irish, Italian American, Russian, Jewish, and Serbian might all be groups whose members are predominantly included in the “white” racial category.

Shared geography, language, and religion can often, but not always, factor into ethnic group categorizations. Ethnic groups distinguish themselves differently from one period to another. Ethnic identity can be used by individuals to identify themselves with others who have shared geographic, cultural, historical, linguistic, and religious ancestry; however, like race, ethnicity has been defined by the stereotypes created by dominant groups as a method of “Othering.” Othering is a process in which one group, usually the dominant group, views and represents themselves as “us/same” and another group as “them/other.”

Ethnicity, like race, continues to be an identification method that individuals and institutions use today—whether through the census, affirmative action initiatives, nondiscrimination laws, or simply in day-to-day personal relations.

Intergroup Relationships

Intergroup relations (relationships between different groups of people) range along a spectrum between tolerance and intolerance. The most tolerant form of intergroup relations is pluralism, in which no distinction is made between minority and majority groups, but instead, there is equal standing. At the other end of the continuum are amalgamation, expulsion, ethnic cleansing, and even genocide – stark examples of intolerant intergroup relations.

Ethnic Cleansing and Genocide

The 20th Century was also the deadliest century, regarding war, in human history.  This century experienced two world wars, multiple civil wars, genocides in Rwanda (Tutsis and moderate Hutus), Sudan, Yugoslavia, and the Holocaust that decimated the Jewish population in Europe during WWII. In addition to WWI and WWII, this century experienced the Korean War, the Vietnam War, the Cold War, and the first Gulf War. Additionally, this century saw regional and civil conflicts such as those experienced in the Congo (6 million people died), as well as an upsurge in child soldiers and modern slavery.

Some of the worst acts by humans have been concerning ethnic cleansing and genocide. The United Nations Security Council established Resolution 780, which states that ethnic cleansing is “a purposeful policy designed by one ethnic or religious group to remove by violent and terror-inspiring means the civilian population of another ethnic or religious group from certain geographic areas.”

Genocide is usually defined as the intentional killing of large sums of people targeted because of their ethnicity, political ideology, religion, or culture. At first glance, it appears that ethnic cleansing and genocide are similar. With ethnic cleansing, the aim is to remove a group of people with similar ethnic backgrounds from a specific geographic region by any means possible. This could include forced migration, terror and rape, destruction of villages, and large-scale death. With genocide, the real intent is the death of a group of people at any scale possible until they are extinct. This has happened many times in recent history including Bosnia-Herzegovina, Burma, Cambodia, the Democratic Republic of the Congo, Rwanda, Sudan, and now Syria. Sadly, with all these ethnic conflicts, most were not officially declared as genocides by the United Nations Security Council, but the conditions on the ground and the reasons why they were occurring fit the definition.

The treatment of aboriginal Australians is also an example of genocide committed against indigenous people. Historical accounts suggest that between 1824 and 1908, white settlers killed more than 10,000 native Aborigines in Tasmania and Australia (Tatz 2006).

Another example is the European colonization of North America. Some historians estimate that Native American populations dwindled from approximately 12 million people in the year 1500 to barely 237,000 by the year 1900 (Lewy 2004). European settlers coerced American Indians off their lands, often causing thousands of deaths in forced removals, such as occurred in the Cherokee or Potawatomi Trail of Tears.

Settlers also enslaved Native Americans and forced them to give up their religious and cultural practices. However, the primary cause of Native American death was neither slavery nor war nor forced removal: it was the introduction of European diseases and Indians’ lack of immunity to them. Smallpox, diphtheria, and measles flourished among indigenous American tribes who had no exposure to the diseases and no ability to fight them. Quite simply, these diseases decimated the tribes. How planned this genocide was remains a topic of contention. Some argue that the spread of disease was an unintended effect of conquest, while others believe it was intentional citing rumors of smallpox-infected blankets being distributed as “gifts” to tribes.

Genocide is not just a historical concept; it is practiced today. Recently, ethnic and geographic conflicts in the Darfur region of Sudan have led to hundreds of thousands of deaths. As part of an ongoing land conflict, the Sudanese government and their state-sponsored Janjaweed militia have led a campaign of killing, forced displacement, and systematic rape of Darfuri people. Although a treaty was signed in 2011, the peace is fragile.

Today, there are a few situations that may be classified as a genocide. The first is in Myanmar, where the Buddhist government has been systematically driving out Muslim populations called Rohingya.

In July 2011, South Sudan became the world’s newest country when it voted to break away from Sudan. Yet by December 2013, fighting between the new government and rebel fighters created a new civil war within the new country. Thousands of civilians have been killed, with millions more displaced by the violence. Like Yemen, there is now growing concern that the civil war will create a nationwide famine.


Segregation refers to the physical separation of two groups, particularly in residence, but also in the workplace and social functions. It is essential to distinguish between de jure segregation (segregation that is enforced by law) and de facto segregation (segregation that occurs without laws but because of other factors). A stark example of de jure segregation is the apartheid movement of South Africa, which existed from 1948 to 1994. Under apartheid, black South Africans were stripped of their civil rights, and forcibly relocated to areas that segregated them physically from their white compatriots. Only after decades of degradation, violent uprisings, and international advocacy was apartheid finally abolished.

Thumbnail for the embedded element "Apartheid: The rise and fall of South Africa's 'apartness' laws"

A YouTube element has been excluded from this version of the text. You can view it online here:



Pluralism is represented by the ideal of the United States as a “salad bowl”: a great mixture of different cultures where each culture retains its own identity and yet adds to the flavor of the whole. Genuine pluralism is characterized by mutual respect on the part of all cultures, both dominant and subordinate, creating a multicultural environment of acceptance. In reality, true pluralism is a challenging goal to reach. In the United States, the mutual respect required by pluralism is often missing, and the nation’s past pluralist model of a melting pot posits a society where cultural differences aren’t embraced as much as erased.


Assimilation describes the process by which a minority individual or group gives up its own identity by taking on the characteristics of the dominant culture. In the United States, which has a history of welcoming and absorbing immigrants from different lands, assimilation has been a function of immigration.

Most people in the United States have immigrant ancestors. In relatively recent history, between 1890 and 1920, the United States became home to around 24 million immigrants. In the decades since then, further waves of immigrants have come to these shores and have eventually been absorbed into U.S. culture, sometimes after facing extended periods of prejudice and discrimination. Assimilation may lead to the loss of the minority group’s cultural identity as they become absorbed into the dominant culture, but assimilation has minimal to no impact on the majority group’s cultural identity.

Some groups may keep only symbolic gestures of their original ethnicity. For instance, many Irish Americans may celebrate Saint Patrick’s Day, many Hindu Americans enjoy a Diwali festival, and many Mexican Americans may celebrate Cinco de Mayo (a May 5 acknowledgment of Mexico’s victory at the 1862 Battle of Puebla). However, for the rest of the year, other aspects of their originating culture may be forgotten.

Assimilation is antithetical to the “salad bowl” created by pluralism; rather than maintaining their cultural flavor, subordinate cultures give up their traditions in order to conform to their new environment. Social scientists measure the degree to which immigrants have assimilated to a new culture with four benchmarks: socioeconomic status, spatial concentration, language assimilation, and intermarriage. When faced with racial and ethnic discrimination, it can be difficult for new immigrants to assimilate fully. Language assimilation, in particular, can be a formidable barrier, limiting employment and educational options and therefore constraining growth in socioeconomic status.


Amalgamation is the process by which a minority group and a majority group combine to form a new group. Amalgamation creates the classic “melting pot” analogy; unlike the “salad bowl,” in which each culture retains its individuality, the “melting pot” ideal sees the combination of cultures that results in a new culture entirely.

Amalgamation, also known as miscegenation, is achieved through intermarriage between races. In the United States, anti-miscegenation laws flourished in the South during the Jim Crow era. It was not until 1967’s Loving v. Virginia that the last anti-miscegenation law was struck from the books, making these laws unconstitutional.

8.2: Understanding Culture

Defining Culture

Humans are social creatures. Since the dawn of Homo sapiens nearly 250,000 years ago, people have grouped into communities in order to survive. Living together, people form everyday habits and behaviors – from specific methods of childrearing to preferred techniques for obtaining food. In modern-day Paris, many people shop daily at outdoor markets to pick up what they need for their evening meal, buying cheese, meat, and vegetables from different specialty stalls. In the United States, the majority of people shop once a week at supermarkets, filling large carts to the brim. How would a Parisian perceive U.S. shopping behaviors that Americans take for granted?

Almost every human behavior, from shopping to marriage to expressions of feelings, is learned. In the United States, people tend to view marriage as a choice between two people, based on mutual feelings of love. In other nations and in other times, marriages have been arranged through an intricate process of interviews and negotiations between entire families, or in other cases, through a direct system, such as a “mail-order bride.” To someone raised in New York City, the marriage customs of a family from Nigeria may seem strange or even wrong. Conversely, someone from a traditional Kolkata family might be perplexed with the idea of romantic love as the foundation for marriage and lifelong commitment. In other words, how people view marriage depends mostly on what they have been taught.

Behavior based on learned customs is not a bad thing. Being familiar with unwritten rules helps people feel secure and “normal.” Most people want to live their daily lives, confident that their behaviors will not be challenged or disrupted — however, even action as seemingly simple as commuting to work evidences a great deal of cultural propriety.

Culture consists of thoughts and tangible things. Material culture refers to the objects or belongings of a group of people. Nonmaterial culture, in contrast, consists of the ideas, attitudes, and beliefs of a society. Material and nonmaterial aspects of culture are linked, and physical objects often symbolize cultural ideas. These material and nonmaterial aspects of culture can vary subtly from region to region.

Ethnocentrism and Cultural Relativism

Despite how much humans have in common, cultural differences are far more prevalent than cultural universals. For example, while all cultures have language, analysis of particular language structures and conversational etiquette reveal tremendous differences. In some Middle Eastern cultures, it is common to stand close to others in conversation. North Americans keep more distance and maintain an ample “personal space.” Even something as simple as eating and drinking varies significantly from culture to culture. If your professor comes into an early morning class holding a mug of liquid, what do you assume she is drinking? In the United States, it’s most likely filled with coffee, not Earl Grey tea, a favorite in England, or Yak Butter tea, a staple in Tibet.

The way cuisines vary across cultures fascinates many people. Some travelers pride themselves on their willingness to try unfamiliar foods, like celebrated food writer Anthony Bourdain, while others return home expressing gratitude for their native culture’s fare. Often, people in the United States express disgust at other cultures’ cuisine and think that it is gross to eat meat from a dog or guinea pig, for example, while they do not question their habit of eating cows or pigs. Such attitudes are an example of ethnocentrism, or evaluating and judging another culture based on how it compares to one’s cultural norms. Ethnocentrism, as social scientists William Graham Sumner (1906) described the term, involves a belief or attitude that one’s own culture is better than all others. Almost everyone is a little bit ethnocentric. For example, Americans tend to say that people from England drive on the “wrong” side of the road, rather than on the “other” side. Someone from a country where dog meat is standard fare might find it off-putting to see a dog in a French restaurant—not on the menu, but as a pet and patron’s companion. An example of ethnocentrism is referring to parts of Asia as the “Far East.” One might question, “Far East of where?”

A high level of appreciation for one’s own culture can be healthy; a shared sense of community pride, for example, connects people in a society. However, ethnocentrism can lead to disdain or dislike for other cultures and could cause misunderstanding and conflict. People with the best intentions sometimes travel to a society to “help” its people, because they see them as uneducated or backward – inherently inferior. In reality, these travelers are guilty of cultural imperialism, the deliberate imposition of one’s own cultural values on another culture. Europe’s colonial expansion, begun in the sixteenth century, was often accompanied by a severe cultural imperialism. European colonizers often viewed the people in the lands they colonized as uncultured savages who needed European governance, dress, religion, and other cultural practices. A more modern example of cultural imperialism may include the work of international aid agencies who introduce agricultural methods and plant species from developed countries while overlooking indigenous varieties and agricultural approaches that are better suited to the particular region.

Ethnocentrism can be so strong that when confronted with all of the differences of a new culture, one may experience disorientation and frustration, called culture shock. A traveler from Chicago might find the nightly silence of rural Montana unsettling, not peaceful. An exchange student from China might be annoyed by the constant interruptions in class as other students ask questions – a practice that is considered rude in China. Perhaps the Chicago traveler was initially captivated with Montana’s quiet beauty, and the Chinese student was initially excited to see a U.S.-style classroom firsthand. However, as they experience unanticipated differences from their own culture, their excitement gives way to discomfort and doubts about how to behave appropriately in the new situation. Eventually, as people learn more about a culture, they recover from culture shock.

Culture shock may appear because people are not always expecting cultural differences. Anthropologist Ken Barger (1971) discovered this when he conducted a participatory observation in an Inuit community in the Canadian Arctic. Initially, from Indiana, Barger hesitated when invited to join a local snowshoe race. He knew he would never hold his own against these experts. Sure enough, he finished last, to his mortification. However, the tribal members congratulated him, saying, “You really tried!” In Barger’s own culture, he had learned to value victory. To the Inuit people, winning was enjoyable, but their culture valued survival skills essential to their environment: how hard someone tried could mean the difference between life and death. Throughout his stay, Barger participated in caribou hunts, learned how to take shelter in winter storms, and sometimes went days with little or no food to share among tribal members. Trying hard and working together, two nonmaterial values, were indeed much more important than winning.

During his time with the Inuit tribe, Barger learned to engage in cultural relativism. Cultural relativism is the practice of assessing a culture by its own standards rather than viewing it through the lens of one’s own culture. Practicing cultural relativism requires an open mind and a willingness to consider, and even adapt to, new values and norms. However, indiscriminately embracing everything about a new culture is not always possible. Even the most culturally relativist people from egalitarian societies — ones in which women have political rights and control over their own bodies — would question whether the widespread practice of female genital mutilation in countries such as Ethiopia and Sudan should be accepted as a part of cultural tradition. Human geographers attempting to engage in cultural relativism, then, may struggle to reconcile aspects of their own culture with aspects of a culture that they are studying.

Sometimes when people attempt to rectify feelings of ethnocentrism and develop cultural relativism, they swing too far to the other end of the spectrum. Xenocentrism is the opposite of ethnocentrism, and refers to the belief that another culture is superior to one’s own. (The Greek root word xeno, pronounced “ZEE-no,” means “stranger” or “foreign guest.”) An exchange student who goes home after a semester abroad or a geographer who returns from the field may find it difficult to associate with the values of their own culture after having experienced what they deem a more upright or nobler way of living.

Perhaps the greatest challenge for geographers and other social scientists studying different cultures is the matter of keeping a perspective. It is impossible for anyone to keep all cultural biases at bay; the best we can do is strive to be aware of them. Pride in one’s own culture does not have to lead to imposing its values on others. Moreover, an appreciation for another culture should not preclude individuals from studying it with a critical eye.

Elements of Cultural Values and Beliefs

The first, and perhaps most crucial, elements of culture we will discuss are its values and beliefs. Values are a culture’s standard for discerning what is good and just in society. Values are deeply embedded and critical for transmitting and teaching a culture’s beliefs. Beliefs are the tenets or convictions that people hold to be true. Individuals in a society have specific beliefs, but they also share common values. To illustrate the difference, Americans commonly believe in the American Dream—that anyone who works hard enough will be successful and wealthy. Underlying this belief is the American value that wealth is useful and important.

Values help shape a society by suggesting what is right and wrong, beautiful and ugly, sought, or avoided. Consider the value that the United States places upon youth. Children represent innocence and purity, while a youthful adult appearance signifies sexuality. Shaped by this value, individuals spend millions of dollars each year on cosmetic products and surgeries to look young and beautiful. The United States also has an individualistic culture, meaning people place a high value on individuality and independence. In contrast, many other cultures are collectivist, meaning the welfare of the group and group relationships are a primary value.

Living up to a culture’s values can be difficult. It is easy to value good health, but it is hard to quit smoking. Marital monogamy is valued, but many spouses engage in infidelity. Cultural diversity and equal opportunities for all people are valued in the United States, yet the country’s highest political offices have been dominated by white men.

Values often suggest how people should behave, but they do not accurately reflect how people do behave. Values portray an ideal culture; the standards society would like to embrace and live up to. However, ideal culture differs from real culture, the way society actually is, based on what occurs and exists. In an ideal culture, there would be no traffic accidents, murders, poverty, or racial tension. However, in real culture, police officers, lawmakers, educators, and social workers continuously strive to prevent or repair those accidents, crimes, and injustices

One way societies strive to put values into action is through rewards, sanctions, and punishments. When people observe the norms of society and uphold their values, they are often rewarded. A boy who helps an elderly woman board a bus may receive a smile and a “thank you.” A business manager who raises profit margins may receive a quarterly bonus. People sanction certain behaviors by giving their support, approval, or permission, or by instilling formal actions of disapproval and nonsupport. Sanctions are a form of social control, a way to encourage conformity to cultural norms. Sometimes people conform to norms in anticipation or expectation of positive sanctions: good grades, for instance, may mean praise from parents and teachers. From a criminal justice perspective, properly used social control is also inexpensive crime control. Utilizing social control approaches pushes most people to conform to societal rules, regardless of whether authority figures (such as law enforcement) are present.

When people go against a society’s values, they are punished. A boy who shoves an older woman aside to board the bus first may receive frowns or even a scolding from other passengers. A business manager who drives away customers will likely be fired. Breaking norms and rejecting values can lead to cultural sanctions such as earning a negative label—lazy, no-good bum—or to legal sanctions, such as traffic tickets, fines, or imprisonment.

Values are not static; they vary across time and between groups as people evaluate, debate, and change collective societal beliefs. Values also vary from culture to culture. For example, cultures differ in their values about what kinds of physical closeness are appropriate in public. It is rare to see two male friends or coworkers holding hands in the United States, where that behavior often symbolizes romantic feelings. However, in many nations, masculine physical intimacy is considered natural in public. This difference in cultural values came to light when people reacted to photos of former president George W. Bush holding hands with the Crown Prince of Saudi Arabia in 2005. A simple gesture, such as hand-holding, carries significant symbolic differences across cultures.


So far, the examples in this chapter have often described how people are expected to behave in certain situations – for example, when buying food or boarding a bus. These examples describe the visible and invisible rules of conduct through which societies are structured, or what social scientists call norms. Norms define how to behave in accordance with what a society has defined as good, right, and important, and most members of the society adhere to them.

Formal norms are established, written rules. They are behaviors worked out and agreed upon in order to suit and serve the most people. Laws are formal norms, but so are employee manuals, college entrance exam requirements, and “no running” signs at swimming pools. Formal norms are the most specific and clearly stated of the various types of norms, and they are the most strictly enforced. However, even formal norms are enforced to varying degrees and are reflected in cultural values.

For example, money is highly valued in the United States, so monetary crimes are punished. It is against the law to rob a bank, and banks go to great lengths to prevent such crimes. People safeguard valuable possessions and install anti-theft devices to protect homes and cars. A less strictly enforced social norm is driving while intoxicated. While it is against the law to drive drunk, drinking is, for the most part, an acceptable social behavior. Moreover, though there are laws to punish drunk driving, there are few systems in place to prevent the crime. These examples show a range of enforcement regarding formal norms.

There are plenty of formal norms, but the list of informal norms – casual behaviors that are generally and widely conformed to – is longer. People learn informal norms through observation, imitation, and general socialization. Some informal norms are taught directly, while others are learned by observation, including observations of the consequences when someone else violates a norm. However, although informal norms define personal interactions, they extend into other systems as well. Most people do not commit even benign breaches of informal norms. Informal norms dictate appropriate behaviors without the need for written rules.

Cultural Change

Culture is always evolving. Moreover, new things are added to material culture every day, and they affect nonmaterial culture as well. Cultures change when something new (say, railroads or smartphones) opens up new ways of living and when new ideas enter a culture (say, as a result of travel or globalization).

Innovation: Discovery and Intervention

Innovation refers to an object or concept’s initial appearance in society – it is innovative because it is markedly new. There are two ways to come across an innovative object or idea: discover it or invent it. Discoveries make known previously unknown but existing aspects of reality. In 1610, when Galileo looked through his telescope and discovered Saturn, the planet was already there, but until then, no one had known about it. When Christopher Columbus encountered America, the land was, of course, already well known to its inhabitants. However, Columbus’s discovery was new knowledge for Europeans, and it opened the way to changes in European culture, as well as to the cultures of the discovered lands. For example, new foods such as potatoes and tomatoes transformed the European diet, and horses brought from Europe changed hunting practices of Native American tribes of the Great Plains.

Inventions result when something new is formed from existing objects or concepts—when things are put together in an entirely new manner. In the late 1800s and early 1900s, electric appliances were invented at an astonishing pace. Cars, airplanes, vacuum cleaners, lamps, radios, telephones, and televisions were all new inventions. Inventions may shape a culture when people use them in place of older ways of carrying out activities and relating to others, or as a way to carry out new kinds of activities. Their adoption reflects (and may shape) cultural values, and their use may require new norms for new situations.

Consider the introduction of modern communication technology, such as mobile phones and smartphones. As more and more people began carrying these devices, phone conversations no longer were restricted to homes, offices, and phone booths. People on trains, in restaurants, and other public places became annoyed by listening to one-sided conversations. Norms were needed for cell phone use. Some people pushed for the idea that those who are out in the world should pay attention to their companions and surroundings. However, technology-enabled a workaround such as texting, which enables quiet communication and has surpassed phoning as the leading way to meet today’s highly valued ability to stay in touch anywhere, everywhere.

When the pace of innovation increases, it can lead to generation gaps. A skeptical older generation sometimes dismisses technological gadgets that catch on quickly with one generation. A culture’s objects and ideas can cause not just generational but cultural gaps. Material culture tends to diffuse more quickly than nonmaterial culture; technology can spread through society in a matter of months, but it can take generations for the ideas and beliefs of society to change. Sociologist William F. Ogburn coined the term culture lag to refer to this time that elapses between the introduction of a new item of material culture and its acceptance as part of nonmaterial culture (Ogburn 1957).

Culture lag can also cause tangible problems. The infrastructure of the United States, built a hundred years ago or more, is having trouble supporting today’s more densely populated and fast-paced life. There is a lag in conceptualizing solutions to infrastructure problems. Rising fuel prices, increased air pollution, and traffic jams are all symptoms of culture lag. Although people are becoming aware of the consequences of overusing resources, the means to support changes take time to achieve.

Diffusion and Globalization

The integration of world markets and technological advances of the last decades have allowed for greater exchange between cultures through the processes of globalization and diffusion. Beginning in the 1980s, Western governments began to deregulate social services while granting greater liberties to private businesses. As a result, world markets became dominated by multinational companies in the 1980s, a new state of affairs at that time. We have since come to refer to this integration of international trade and finance markets as globalization. Increased communications and air travel have further opened doors for international business relations, facilitating the flow not only of goods but also of information and people as well (Scheuerman 2014 (revised)). Today, many U.S. companies set up offices in other nations where the costs of resources and labor are cheaper. When a person in the United States calls to get information about banking, insurance, or computer services, the person taking that call may be working in another country.

Alongside the process of globalization is diffusion, or the spread of material and nonmaterial culture. While globalization refers to the integration of markets, diffusion relates to a similar process in the integration of international cultures. Middle-class Americans can fly overseas and return with a new appreciation of Thai noodles or Italian gelato. Access to television and the Internet has brought the lifestyles and values portrayed in U.S. sitcoms into homes around the globe. Twitter feeds from public demonstrations in one nation have encouraged political protesters in other countries. When this kind of diffusion occurs, material objects and ideas from one culture are introduced into another.

Theoretical Perspectives on Culture

Music, fashion, technology, and values—all are products of culture. However, what do they mean? How do human geographers perceive and interpret culture based on these material and nonmaterial items? Let us finish our analysis of culture by reviewing them in the context of three theoretical perspectives: functionalism, conflict theory, and symbolic interactionism.

Functionalists view society as a system in which all parts work—or function—together to create society as a whole. In this way, societies need culture to exist. Cultural norms function to support the fluid operation of society, and cultural values guide people in making choices. Just as members of a society work together to fulfill a society’s needs, culture exists to meet its members’ basic needs.

Functionalists also study culture in terms of values. Education is an essential concept in the United States because it is valued. The culture of education—including material culture such as classrooms, textbooks, libraries, dormitories—supports the emphasis placed on the value of educating a society’s members.

Conflict theorists view social structure as inherently unequal, based on power differentials related to issues like class, gender, race, and age. For a conflict theorist, culture is seen as reinforcing issues of “privilege” for certain groups based upon race, sex, class, and so on. Women strive for equality in a male-dominated society. Senior citizens struggle to protect their rights, their health care, and their independence from a younger generation of lawmakers. Advocacy groups such as the ACLU work to protect the rights of all races and ethnicities in the United States.

Inequalities exist within a culture’s value system. Therefore, a society’s cultural norms benefit some people but hurt others. Some norms, formal and informal, are practiced at the expense of others. Women were not allowed to vote in the United States until 1920. Gay and lesbian couples have been denied the right to marry in some states. Racism and bigotry are very much alive today. Although cultural diversity is supposedly valued in the United States, many people still frown upon interracial marriages. Same-sex marriages are banned in most states, and polygamy—common in some cultures—is unthinkable to most Americans.

At the core of conflict theory is the effect of economic production and materialism: dependence on technology in rich nations versus a lack of technology and education in emerging nations. Conflict theorists believe that a society’s system of material production affects the rest of the culture. People who have less power also have less ability to adapt to cultural change. This view contrasts with the perspective of functionalism. In the U.S. culture of capitalism, to illustrate, we continue to strive toward the promise of the American dream, which perpetuates the belief that the wealthy deserve their privileges.

Symbolic interactionism is a sociological perspective that is most concerned with the face-to-face interactions between members of society. Interactionists see culture as being created and maintained by the ways people interact and in how individuals interpret each other’s actions. Proponents of this theory conceptualize human interactions as a continuous process of deriving meaning from both objects in the environment and the actions of others. This is where the term symbolic comes into play. Every object and action has a symbolic meaning, and language serves as a means for people to represent and communicate their interpretations of these meanings to others. Those who believe in symbolic interactionism perceive culture as highly dynamic and fluid, as it is dependent on how meaning is interpreted and how individuals interact when conveying these meanings.

We began this chapter by asking what culture is. Culture is comprised of all the practices, beliefs, and behaviors of a society. Because culture is learned, it includes how people think and express themselves. While we may like to consider ourselves individuals, we must acknowledge the impact of culture; we inherit thought language that shapes our perceptions and patterned behavior, including about issues of family and friends, and faith and politics.

To an extent, culture is a social comfort. After all, sharing a similar culture with others is precisely what defines societies. Nations would not exist if people did not coexist culturally. There could be no societies if people did not share heritage and language, and civilization would cease to function if people did not agree on similar values and systems of social control. Culture is preserved through transmission from one generation to the next, but it also evolves through processes of innovation, discovery, and cultural diffusion. We may be restricted by the confines of our own culture, but as humans, we can question values and make conscious decisions. No better evidence of this freedom exists than the amount of cultural diversity within our society and around the world. The more we study another culture, the better we become at understanding our own.


Environmental determinism argues that both general features and regional variations of human cultures and societies are determined by the physical and biological forms that make up the earth’s many natural landscapes. Geographers influenced by Semple and Huntington tended to describe and explain what they believed to be “superior” European culture (civilization) through the application of the theory of environmental determinism. From their writings, it does not seem that they ever recognized the inaccuracies of their position, let alone the arrogant, racist foundation upon which it rested.

Although modern geographers rarely discuss the impacts of environmental determinism except to note its serious flaws as a model for spatial analysis, its basic concepts were used by the Third Reich to justify German expansion in the 1930s and 1940s. Friedrich Ratzel, a German geographer (American geographer, Ellen Churchill Semple was one of his students) argued that nation states are organic and therefore, must grow in order to survive. In other words, states must continually seek additional “lebensraum” (living room). The state, a living thing, was a natural link between the people and the natural environment (blood and soil). Moreover, the state provided a living tie between people and a place. This application of environmental determinism, and Social Darwinism, eventually came to be more than a mere academic exercise because it was used to justify, or legitimize, the conquering of one people by another. At the height of European imperialism, academics depicted the tremendous colonial empires as natural extensions of superior European cultures that had developed in the beneficial natural surrounding of the mid-latitudes. The concept of “manifest destiny” was used similarly to justify the expansion of the United States from the Atlantic to Pacific shores, at the expense of indigenous people.

Although Ratzel, Semple, and Huntington never expected their ideas to be used to justify Adolf Hitler’s conquest of Europe, Nazi geographers and political scientists built upon their work to develop theories of Nordic racial and cultural superiority. Semple and Huntington wanted nothing more than to define the boundaries of their discipline and to explain the differences in “cultures” and “places” throughout the world. They were merely striving to carve out a piece of academic or intellectual turf for themselves and like-minded colleagues.

By the 1920s, environmental determinism was already under attack by people such as Carl Sauer (at the University of California, Berkeley). Nevertheless, many scholars continued to base their work on the belief that human beings are primarily a product of the environment in which they live. Frederick Jackson Turner, the American historian who eloquently described the westward expansion of the United States, and Sir Halford Mackinder, the British political scientist who developed the “Heartland Theory,” explained away the conquering of indigenous people by Europeans as perhaps regrettable, but nonetheless, natural and unavoidable (given the superiority of cultures spawned in the mid-latitude environs of Western Europe).

The Cultural Landscape

Carl Sauer was probably the most influential cultural geographer of the twentieth century. Sauer’s work is characterized by a focus on the material landscape tempered with an abiding interest in human ecology, and the damaging impacts of humans on the environment. Additionally, and of equal importance, Sauer worked tirelessly to trace the origins and diffusions of cultural practices such as agriculture, the domestication of animals, and the use of fire.

Although there is no question that Sauer’s contributions to cultural geography are of great worth, some also criticize him for an anti-modern, anti-urban bias. Even so, his efforts to correct the inherent flaws associated with “environmental determinism” significantly strengthened the discipline of geography, and cultural geography in particular.

In 1925, Sauer published The Morphology of Landscape. In this work, he sought to demonstrate that nature does not create culture, but instead, culture working with and on nature, creates ways-of-life. Sauer considered human impacts on the landscape to be a manifestation of culture. Therefore, he argued, in order to understand a culture, a geographer must learn to read the landscape.

Sauer looked at “culture” holistically. Simply put, Sauer regarded “culture” as a way of life. Sauer, however, did not fully develop an explanation of what “culture” is. Instead, he left it to anthropologist Franz Boas to debunk “environmental determinism” and “social Darwinism” and to call for the analysis of cultures on “their” own terms (as opposed to using a hierarchical ranking system). Although mildly rooted in “cultural relativism,” he was not interested in necessarily justifying cultural practices. To the contrary, he wanted to eliminate the application of personal biases when studying cultures (as in Mitchell, Don, Cultural Geography: A Critical Introduction).

8.3: Geography of World Languages

Language and religion are two essential cultural characteristics for human geographers to study. Geographers describe the historical and spatial distributions of language and religion across the landscape as a way of understanding cultural identity. Furthermore, when geographers study religion, they are less concerned with theology and more concerned with the diffusion and interaction of religious ideologies across time and space and the imprint it has on the cultural landscape.

Defining Language

Language and religion are two essential cultural characteristics for human geographers to study. Geographers describe the historical and spatial distributions of language and religion across the landscape as a way of understanding cultural identity. Furthermore, when geographers study religion, they are less concerned with theology and more concerned with the diffusion and interaction of religious ideologies across time and space and the imprint it has on the cultural landscape.

Languages relate to each other in much the same way that family groups (think of a family tree) relate to each other. Language is a system of communication that provides meaning to a group of people through speech. Nearly all languages around the world have a literary tradition: a system of written communication. Most nations have an official language. Most citizens of a nation with an official language speak and write in that language. Additionally, most official or governmental documents, monetary funds, and transportation signs are communicated in the official language. However, some regions, such as the European Union have 23 official languages.

A language family is a collection of languages related through a common prehistorical language that makes up the main trunk of language identity. A language tree will have language branches, a collection of languages related through a common ancestral language that existed thousands of years ago. Finally, a language group is a collection of languages within a single branch that shares a common origin from the relatively recent past and displays relatively few differences in grammar and vocabulary.


There are various dialects within any language, and English in the United States is no exception. A dialect is a regional variation of a language, such as English, distinguished by distinctive vocabulary, spelling, and pronunciation. In the United States, there is a dialect difference between southern, northern, and western states. We can all understand each other, but the way we say things may sound accented or “weird” to others. There is also a dialect difference between American English and English spoken in Britain, as well as other parts of the British Commonwealth.

Origins and Diffusions of Language

All modern languages originate from an ancient language. The origin of every language may never be known because many ancient languages existed and changed before the written record. Root words within languages are the best evidence that we have to indicate that languages originated from pre-written history. The possible geographic origin of ancient languages is quite impressive. For example, several languages have similar root words for winter and snow, but not for the ocean. This indicates that the original language originated in an interior location away from the ocean. It was not until people speaking this language migrated toward the ocean that the word ocean was added to the lexicon (a catalog of a language’s words).

There are many layers within the Indo-European language family, but we will focus on the specifics. Though they sound very different, German and English, come from the same Germanic branch of the Indo-European language group. The Germanic branch is divided into High German and Low German. Most Germans speak High German, whereas English, Danish, and Flemish are considered subgroups of Low German. The Romance branch originated 2,000 years ago and is derived from Latin. Today, the Romance languages are Spanish, Portuguese, French, and Italian. The Balto-Slavic branch uses to be considered one broad language called Slavic in the 7th Century, but subdivided into a variety of smaller groups over time. Today the Balto-Slavic branch is composed of the following groups: East Slavic, West, Slavic, South Slavic, and Baltic. The Indo-European language branch spoken by most people around the world is Indo-Iranian with over 100 individual languages.

The origin of Indo-European languages has long been a topic of debate among scholars and scientists. In 2012, a team of evolutionary biologists at the University of Auckland led by Dr. Quentin Atkinson released a study that found all modern IE languages could be traced back to a single root: Anatolian — the language of Anatolia, now modern-day Turkey.

Distribution of Language Families

The next question that must be asked is why languages are diffused where they are diffused?  Social scientists, specifically linguistics and archaeologists, disagree on this issue because some believe that languages are diffused by war and conquest, whereas others believe diffusion occurs by peaceful/symbiotic means such as food and trade. For example, English is spoken by over 2 billion people and is the dominant language in 55 countries. Much of this diffusion has to do with British imperialism. The primary purpose of British imperialism was to appropriate as much foreign territory as possible to use as sources of raw materials. Imperialism involves diffusion of language through both conquest and trade.

The linguistic structure of the Sino-Tibetan language family is very complex and different from the Indo-European language family. Unlike European languages, the Sino-Tibetan language is based on hundreds of one-syllable spoken words. The other distinctive characteristic of this language is the way it is written. Rather than letters used in the Indo-European language, the Chinese language is written using thousands of characters called ideograms, which represent ideas or concepts rather than sounds. Sino-Tibetan language family exists mainly in China—the most populous nation in the world—and is over 4,000 years old. Of the over 1 billion Chinese citizens, 75 percent speak Mandarin, making it the most common language used in the world.

There are a large variety of other language families in Eastern and Southeast Asian. There is Austronesian in Indonesia, Austro-Asiatic that includes Vietnamese, Tai Kadai that is spoken in Thailand and surrounding countries, Korean and Japanese. In Southwest Asia (also called the Middle East), there are three dominant language families. The Afro-Asiatic languages are spoken by over 200 million people in several countries in the form of Arabic and are the written language of the Muslim holy book called the Quran. Hebrew is another Afro-Asiatic language and is the language of the Torah and Talmud (Jewish sacred texts).

The largest group of the Altaic language family is Turkish. The Turkish language used to be written with Arabic letters, but in 1928 the Turkish government required the use of the Roman alphabet in order to adapt the nation’s cultural and economic communications to those in line with their Western-European counterparts. Finally, the Uralic language family originated 7,000 years ago, near the Ural mountains in Siberia. All European countries speak Indo-European languages except Estonia, Finland, and Hungary, which speak Uralic instead.

The countries that make up Africa have a wealthy and sophisticated family of languages.  Africa has thousands of languages that have resulted from 5,000 years of isolation between the various tribes. Just like species that evolve differently over thousands of years of isolation, Africa’s languages have evolved into various tongues. However, there are three major African language families to focus on. The Niger-Congo language family is spoken by 95 percent of the people in sub-Saharan Africa. Within the Niger-Congo language is Swahili, which is the official language of only 800,00 people, but a secondary language is spoken by over 30 million Africans. Only a few million people in Africa speak languages from the Nilo-Saharan language family. The Khoisan language family is spoken by even fewer, but is distinctive because of the “clicking sounds” when spoken.

In a world dominated by communication, globalization, science, and the Internet, English has grown to be the dominant global language. Today English is considered a lingua franca (a language mutually understood and commonly used in trade by people who have different native languages). It is now believed that 500 million people speak English as a second language. There are other lingua fraca such as Swahili in Eastern Africa and Russian in nations that were once a part of the Soviet Union.

Endangered Languages and Preserving Language Diversity

An isolated language is one that is unrelated to any other language. Thus it cannot be connected to any language family. These remote languages, and many others, are experiencing a mass extinction and are quickly disappearing off the planet. It is believed that nearly 500 languages are in danger of being lost forever. Think about the language you speak, the knowledge and understanding acquired and discovered through that language. What would happen to all that knowledge if your language suddenly disappeared? Would all of it be transferred to another language or would major components be lost to time and be rewritten by history? What would happen to your culture if your language was lost to time? Ultimately, is it possible that the Information Age is causing a Dis-information Age as thousands of languages are near extinction? Click here to view an Esri story map on Endangered Languages.

Consider the impact of language on culture, particularly religion. Most religions have some form of written or literary tradition or history, which allows for information to be transferred to future generations.  However, some religions are only transferred verbally, and when that culture disappears (which is happening at a frightening rate), so does all of the knowledge and history of that culture.

The Endangered Languages Project serves as an online resource for samples and research on endangered languages, as well as a forum for advice and best practices for those working to strengthen linguistic diversity.

8.4: Geography of World Religions

Origins and diffusion of World Religions

Our world’s cultural geography is very complex with language and religion as two cultural traits that contribute to the richness, diversity, and complexity of the human experience. Nowadays, the word “diversity” is gaining a great deal of attention, as nations around the world are becoming more culturally, religiously, and linguistically complex and interconnected. Specifically, in regards to religion, these prestigious cultural institutions are no longer isolated in their place of origin, but have diffused into other realms and regions with their religious history and cultural dominance. In some parts of the world, this has caused religious wars and persecution; in other regions, it has helped initiate cultural tolerance and respect for others.

These trends are, in some ways, the product of a history of migratory push and pull factors along with a demographic change that have brought together peoples of diverse religious and even linguistic backgrounds. It is critical that people critically learn about diverse cultures by understanding important cultural traits, such as the ways we communicate and maintain spiritual beliefs. Geographers need to be aware that even though our discipline might not be able to answer numerous questions related to language structure or address unique aspects of theological opinion, our field can provide insight by studying these cultural traits in a spatial context. In essence, geography provides us with the necessary tools to understand the spread of cultural traits and the role of geographic factors, both physical and cultural, in that process. People will then see that geography has influenced the distribution and diffusion of differing ideologies, as well as the diverse ways they practice their spiritual traditions.

As is the case with languages, geographers have a method of classifying religions so people can better understand the geographic diffusion of belief systems. Although religions are by themselves complex cultural institutions, the primary method for categorizing them is simple. In essence, there are two main groups: universalizing religions, which actively invite non-members to join them, and ethnic religions, which are associated with particular ethnic or national groups. Everyone can recount moments in his or her life in which there was interaction with individuals eager to share with others their spiritual beliefs and traditions. Also, that same person might have encountered individuals who are very private, perhaps secretive, when it comes to personal religious traditions deemed by this individual as exclusive to his or her family and the national group. A discussion of these life experiences can generate fascinating examples that serve as testimony to our world’s cultural richness when it comes to different religious traditions.

Origins of World Religions

A significant portion of the world’s universalizing religions has a precise hearth or place of origin. This designation is based on events in the life of a man, and the hearths where the largest universalizing religions originated are all in Asia. Of course, not all religions are from Asia. The three universalizing religions diffused from specific hearths, or places of origin, to other regions of the world. The hearths where each of these three largest universalizing religions originated are based on the events in the lives of key individuals within each religion. Together, Christianity, Islam, and Buddhism have over 2.5 billion adherents combined.

Religious Conflict

Religion is often the catalyst of conflict between local values or traditions with issues and values that come with nationalism or even globalization. Religion tends to represent core beliefs that represent cultural values and identity, which, along with language, often represent local ideology rather than national or international ideology. There are some reasons why, but some include:

Types of World Religions

The major religions of the world (Hinduism, Buddhism, Islam, Confucianism, Christianity, Taoism, and Judaism) differ in many respects, including how each religion is organized and the belief system each upholds. Other differences include the nature of belief in a higher power, the history of how the world and the religion began, and the use of sacred texts and objects.

Note that some religions may be practiced – or understood – in various categories. For instance, the Christian notion of the Holy Trinity (God, Jesus, Holy Spirit) defies the definition of monotheism, which is a religion based on a belief in a single deity, to some scholars. Similarly, many Westerners view the multiple manifestations of Hinduism’s godhead as polytheistic, which is a religion based on a belief in multiple deities,, while Hindus might describe those manifestations are a monotheistic parallel to the Christian Trinity. Some Japanese practice Shinto, which follows animism, which is a religion that believes in the divinity of nonhuman beings, like animals, plants, and objects of the natural world, while people who practice totemism believe in a divine connection between humans and other natural beings.

It is also important to note that every society also has nonbelievers, such as atheists, who do not believe in a divine being or entity, and agnostics, who hold that ultimate reality (such as God) is unknowable. While typically not an organized group, atheists and agnostics represent a significant portion of the population. It is essential to recognize that being a nonbeliever in a divine entity does not mean the individual subscribes to no morality. Indeed, many Nobel Peace Prize winners and other great humanitarians over the centuries would have classified themselves as atheists or agnostics.

Religions have emerged and developed across the world. Some have been short-lived, while others have persisted and grown. In this section, we will explore seven of the world’s major religions.


The oldest religion in the world, Hinduism originated in the Indus River Valley about 4,500 years ago in what is now modern-day northwest India and Pakistan. It arose contemporaneously with ancient Egyptian and Mesopotamian cultures. With roughly one billion followers, Hinduism is the third-largest of the world’s religions. Hindus believe in a divine power that can manifest as different entities. Three main incarnations—Brahma, Vishnu, and Shiva—are sometimes compared to the manifestations of the divine in the Christian Trinity.

Multiple sacred texts, collectively called the Vedas, contain hymns and rituals from ancient India and are mostly written in Sanskrit. Hindus generally believe in a set of principles called dharma, which refers to one’s duty in the world that corresponds with “right” actions. Hindus also believe in karma, or the notion that spiritual ramifications of one’s actions are balanced cyclically in this life or a future life (reincarnation).


Buddhism was founded by Siddhartha Gautama around 500 B.C.E. Siddhartha was said to have given up a comfortable, upper-class life to follow one of poverty and spiritual devotion. At the age of thirty-five, he famously meditated under a sacred fig tree and vowed not to rise before he achieved enlightenment (bodhi). After this experience, he became known as Buddha, or “enlightened one.” Followers were drawn to Buddha’s teachings and the practice of meditation, and he later established a monastic order.

Buddha’s teachings encourage Buddhists to lead a moral life by accepting the four Noble Truths: 1) life is suffering, 2) suffering arises from attachment to desires, 3) suffering ceases when attachment to desires ceases, and 4) freedom from suffering is possible by following the “middle way.” The concept of the “middle way” is central to Buddhist thinking, which encourages people to live in the present and to practice acceptance of others (Smith 1991). Buddhism also tends to deemphasize the role of a godhead, instead of stressing the importance of personal responsibility (Craig 2002).


Confucianism was the official religion of China from 200 B.C.E. until it was officially abolished when communist leadership discouraged the religious practice in 1949. The religion was developed by Kung Fu-Tzu (Confucius), who lived in the sixth and fifth centuries B.C.E. An extraordinary teacher, his lessons—which were about self-discipline, respect for authority and tradition, and jen (the kind treatment of every person)—were collected in a book called the Analects.

Some religious scholars consider Confucianism more of a social system than a religion because it focuses on sharing wisdom about moral practices but does not involve any specific worship; nor does it have formal objects. Its teachings were developed in the context of problems of social anarchy and a near-complete deterioration of social cohesion. Dissatisfied with the social solutions put forth, Kung Fu-Tzu developed his model of religious morality to help guide society (Smith 1991).


In Taoism, the purpose of life is inner peace and harmony. Tao is usually translated as “way” or “path.” The founder of the religion is generally recognized to be a man named Laozi, who lived sometime in the sixth century B.C.E. in China. Taoist beliefs emphasize the virtues of compassion and moderation.

The central concept of tao can be understood to describe a spiritual reality, the order of the universe, or the way of modern life in harmony with the former two. The ying-yang symbol and the concept of polar forces are central Taoist ideas (Smith 1991). Some scholars have compared this Chinese tradition to its Confucian counterpart by saying that “whereas Confucianism is concerned with day-to-day rules of conduct, Taoism is concerned with a more spiritual level of being” (Feng and English 1972).


After their Exodus from Egypt in the thirteenth century B.C.E., Jews, a nomadic society, became monotheistic, worshipping only one God. The Jews’ covenant, or promise of a special relationship with Yahweh (God), is an essential element of Judaism, and their sacred text is the Torah, which Christians also follow as the first five books of the Bible. Talmud refers to a collection of sacred Jewish oral interpretation of the Torah. Jews emphasize moral behavior and action in this world as opposed to beliefs or personal salvation in the next world.


Probably one of the most misunderstood religions in the world is Islam. Though predominantly centered in the Middle East and Northern Africa, Islam is the fastest growing religion in the world with 1.3 billion and is only second to Christianity is members. Islam is also divided into two major branches: Sunni and Shiite. The Sunni branch is the largest, composed of 83 percent of all Muslims. The Shiite branch is more concentrated in clusters such as Iran, Iraq, and Pakistan.

Islam is monotheistic religion and it follows the teaching of the prophet Muhammad, born in Mecca, Saudi Arabia, in 570 C.E. Muhammad is seen only as a prophet, not as a divine being, and he is believed to be the messenger of Allah (God), who is divine. The followers of Islam, whose U.S. population is projected to double in the next twenty years (Pew Research Forum 2011), are called Muslims.

Islam means “peace” and “submission.” The sacred text for Muslims is the Qur’an (or Koran). As with Christianity’s Old Testament, many of the Qur’an stories are shared with the Jewish faith. Divisions exist within Islam, but all Muslims are guided by five beliefs or practices, often called “pillars”: 1) Allah is the only god, and Muhammad is his prophet, 2) daily prayer, 3) helping those in poverty, 4) fasting as a spiritual practice, and 5) pilgrimage to the holy center of Mecca.

In Western nations, the primary loyalty of the population is to the state. In the Islamic world, however, loyalty to a nation-state is trumped by dedication to religion and loyalty to one’s family, extended family, tribal group, and culture. In regions dominated by Islam, tribalism and religion play determining roles in the operation of social, economic, cultural, and political systems. As a result, the nation states within the Islamic civilization are weak and generally ineffectual. Instead of nationalism, Muslims are far more interested in identifying with “ummah,” (Islamic civilization).

Furthermore, despite the lack of a core Islamic state, the leaders of the many Muslim nations created (1969) the Organization of the Islamic Conference in order to foster a sense of solidarity between Muslim states. Almost all nations with large Muslim populations are now members of the organization. Additionally, some of the more powerful Muslim states have sponsored the World Muslim Conference and the Muslim League to bring Muslims together in a unified block.


Today the largest religion in the world, Christianity began 2,000 years ago in Palestine, with Jesus of Nazareth, a charismatic leader who taught his followers about caritas (charity) or treating others as you would like to be treated yourself.

The sacred text for Christians is the Bible. While Jews, Christians, and Muslims share many of same historical religious stories, their beliefs verge. In their shared sacred stories, it is suggested that the son of God—a messiah—will return to save God’s followers. While Christians believe that he already appeared in the person of Jesus Christ, Jews and Muslims disagree. While they recognize Christ as a prominent historical figure, their traditions do not believe he is the son of God, and their faiths see the prophecy of the Messiah’s arrival as not yet fulfilled.

Different Christian groups have variations among their sacred texts. For instance, Mormons, an established Christian sect, also use the Book of Mormon, which they believe details other parts of Christian doctrine and Jesus’ life that is not included in the Bible. Similarly, the Catholic Bible includes the Apocrypha, a collection that, while part of the 1611 King James translation, is no longer included in Protestant versions of the Bible. Although monotheistic, Christians often describe their god through three manifestations that they call the Holy Trinity: the father (God), the son (Jesus), and the Holy Spirit. The Holy Spirit is a term Christians often use to describe the religious experience, or how they feel the presence of the sacred in their lives. One foundation of Christian doctrine is the Ten Commandments, which decry acts considered sinful, including theft, murder, and adultery.


Some of the places that in some ways contributed to the foundation and development of a faith frequently gain sacred status, either by the presence of a natural site ascribed as holy, or as the stage for miraculous events, or by some historical event such as the erection of a temple.  When a place gains that “sacred” reputation, it is not unusual to see peoples from different parts of the world traveling or making a pilgrimage to this site with the hope of experiencing spiritual and physical renewal.

Buddhists have eight holy sites because they have special meaning or essential events during the Buddha’s life. The first one is in Lumbini, Nepal where the Buddha was born around 563 B.C. The second holy site is in Bodh Gaya, Nepal, where it is believed Siddhartha reached enlightenment to become the Buddha. The third most important site is in Sarnath, India where he gave his first sermon. The fourth holiest site is Kusinagara, India where the Buddha died at the age of 80 and became enlightened. The other four holy sites are where Buddha performed/experienced specific miracles. People who practice Buddhism or Shintoism erect and use pagodas to house relics and sacred texts. Pagodas are also used for individual prayer and meditation.

Islam’s holiest sites are located in Saudi Arabia. The holiest city is Mecca, Saudi Arabia where the Prophet Muhammad was born. It is also the location of the religion’s holiest objects called the Ka’ba, a cube-like structure believed to have been built by Abraham and Ishmael. The second holiest site to Muslims in Medina, Saudi Arabia where Muhammad began his leadership and gained initial support from the people. Every healthy and financially able Muslim is supposed to make at least one pilgrimage to Mecca in their lifetime. For Muslims, a mosque is considered a holy site of worship, but also a place for community assembly. Usually assembled around a courtyard, the pulpit faces Mecca so that all Muslims pray toward their holiest site. Mosques will have a tower called a minaret where someone summons people to worship.

Meaning lord, master, or power, a Christian church is a place of gathering and worship. Compared to other religions, churches play a more important role because they are created to express values and principles. Churches also play a vital role in the landscape. In earlier days and smaller towns, churches tend to be the most significant buildings. Also because of their importance, Christian religions spend lots of money and commitment to the building and maintenance of their churches.

8.5 References

AJ+. (n.d.-b). South Africa Is Still Under Apartheid | Direct From With Dena Takruri – AJ+. Retrieved from

Al Jazeera English. (n.d.). Ethnic Cleansing of Bosnian Muslims —explained. Retrieved from

AP Human Geography Course Description Effective 2015. (2015). 73.

BBC News. (n.d.). “America is a stolen country.” Retrieved from

Business Insider. (n.d.). Animated map shows how Christianity spread around the world. Retrieved from

Carl O. Sauer. (2019). In Wikipedia. Retrieved from

CBS News. (n.d.). Yemen’s famine could be world’s worst in 100 years. Retrieved from

Chapter 3: Race, Ethnicity, and Culture – Introduction to Human Geography. (n.d.). Retrieved January 25, 2019, from

CrashCourse. (n.d.-a). Buddha and Ashoka: Crash Course World History #6. Retrieved from

CrashCourse. (n.d.-b). Christianity from Judaism to Constantine: Crash Course World History #11. Retrieved from

CrashCourse. (n.d.-c). Islam, the Quran, and the Five Pillars All Without a Flamewar: Crash Course World History #13. Retrieved from

CrashCourse. (n.d.-d). Racial/Ethnic Prejudice & Discrimination: Crash Course Sociology #35. Retrieved from

CrashCourse. (n.d.-e). Religion: Crash Course Sociology #39. Retrieved from

Cultural Intelligence. (n.d.). Retrieved May 29, 2019, from OER Commons website:

Cultures, Subcultures, and Countercultures: Crash Course Sociology #11 – YouTube. (n.d.). Retrieved May 29, 2019, from

Eastern Philosphy – Lao Tzu – YouTube. (n.d.). Retrieved May 29, 2019, from

Endangered Languages Project. (n.d.). Retrieved February 3, 2019, from

Environmental Determinism – Environmental Science – Oxford Bibliographies. (n.d.). Retrieved February 3, 2019, from

Gannon,LiveScience, M. (n.d.). Race Is a Social Construct, Scientists Argue. Retrieved February 3, 2019, from Scientific American website:

Global News. (n.d.). Apartheid: The rise and fall of South Africa’s “apartness” laws. Retrieved from

HISTORY. (n.d.). Japanese-American Internment During WWII | History. Retrieved from

Introduction to Culture – Introduction to Sociology 2e – OpenStax CNX. (n.d.). Retrieved May 29, 2019, from

Islam and Politics: Crash Course World History 216 – YouTube. (n.d.). Retrieved February 3, 2019, from

Maps, E. S. (n.d.). One World, Many Voices: Endangered Languages and Cultural Heritage. Retrieved January 25, 2019, from Esri website:

Morgan, K. (n.d.). Research Guides: Open Educational Resources (OER): Geography. Retrieved May 29, 2019, from //

NowThis World. (n.d.). What’s The Most Common Language In The World? Retrieved from

Organisation of Islamic Cooperation. (n.d.). Retrieved February 3, 2019, from

Project Implicit. (n.d.). Retrieved February 3, 2019, from

RACE – The Power of an Illusion | Ten Things Everyone Should Know. (n.d.). Retrieved February 3, 2019, from

Smith, M., & Sobhan, T. (2018, August 29). Opinion | Capturing Their Genocide on Their Cellphones. The New York Times. Retrieved from

South Sudan may be heading towards genocide – YouTube. (n.d.). Retrieved May 29, 2019, from

Studies Weekly. (n.d.). Segregation and Jim Crow. Retrieved from

TED. (n.d.-a). A young poet tells the story of Darfur | Emtithal Mahmoud. Retrieved from

TED. (n.d.-b). Why I love a country that once betrayed me | George Takei. Retrieved from

TED-Ed. (n.d.-a). How languages evolve – Alex Gendler. Retrieved from

The Definition of Race. (n.d.). Retrieved February 3, 2019, from website:

The US may be aiding war crimes in Yemen – YouTube. (n.d.). Retrieved May 29, 2019, from

Vox. (n.d.-a). American segregation, mapped at day and night. Retrieved from

Wisdom Land. (n.d.). Great Animated Map Shows Origins Of  World’s First Written Languages & How They Spread. Retrieved from

Chapter 9 Political Geography for print only


The 20th century was also the deadliest century, in terms of war, in human history.  This century experienced two world wars, multiple civil wars, genocides in Rwanda (Tutsis and moderate Hutus), Sudan, Yugoslavia, and the Holocaust that decimated the Jewish population in Europe during WWII. In addition to WWI and WWII, this century experienced the Korean War, the Vietnam War, the Cold War, and the first Gulf War. Additionally, this century saw regional and civil conflicts such as those experienced in the Congo (6 million people died), as well as an upsurge in child soldiers and modern slavery.

9.1 Defining Nation-States

The term nation refers to a homogeneous group of people with a common heritage, language, religion, or political ambition. A state is an organized political community acting under a government. States may be classified as sovereign if they are not dependent on, or subject to, any other power or state. States are considered to be subject to external sovereignty, or hegemony if their ultimate sovereignty lies in another state. A federated state is a territorial, constitutional community that forms part of a federation. Such states differ from sovereign states, in that they have transferred a portion of their sovereign powers to a federal government. A location claimed by a sovereign state is called a territory.

To understand the differences between state and nation, consider an example like Poland. The people of Poland have long formed a nation with a shared language and culture, but that nation has, through history, been crosscut by various political borders. Thus, at times, members of the Polish nation have been governed by different states. Today, Poland’s boundaries roughly align with the geographical area where the people of the Polish nation live, and thus Poland can be thought of as a nation state.

States may be classified as sovereign if they are not dependent on, or subject to, any other power or state. Other states are subject to external sovereignty or hegemony where ultimate sovereignty lies in another state. A federated state is a territorial and constitutional community forming part of a federation. Such states differ from sovereign states, in that they have transferred a portion of their sovereign powers to a federal government. When people of the same nation and state come together, there is a true nation-state, wherein most citizens share a common heritage and a united government.

The concept of the state is different from the concept of government. A government is a particular group of people that controls the state apparatus at a given time. In other words, governments are the means through which state power is employed; for example, by applying the rule of law. The rule of law is a legal maxim whereby governmental decisions are made by applying known legal principles. The rule of law is rule not by one person, as in an absolute monarchy, but by laws, as in a democratic republic; no one person can rule and even top government officials are under and ruled by the law.

The concept of the state is also different from the concept of a nation, which refers to a large geographical area, and the people therein who perceive themselves as having a collective identity. The state is a political and geopolitical entity; the nation is a cultural or ethnic entity. The nation-state is a state that self-identifies as deriving its political legitimacy from serving as a sovereign entity for a nation as a sovereign territorial unit. The term nation-state implies that the two geographically coincide.

In classical thought, the state was identified with political society and civil society as a form of the political community. In contrast, modern thought distinguishes the nation-state as a political society from civil society as a form of economic society. Civil society is the arena outside of the family, the state, and the market where people associate to advance common interests. It is sometimes considered to include the family and the private sphere and then referred to as the third sector of society, distinct from government and business.


A colony is a territory that is controlled by a sovereign state. European powers focused on establishing settlements and political power around the world by imposing their military, economic, political, and cultural influence through colonialism. Colonialism is control of previously uninhabited or sparsely inhabited land. Europeans used colonialism to promote political control over religion, extract natural resources, increase economic influence, and to expand political and military power. The European states first colonized the New World of the Americas, but later redirected their focus to Africa and Asia. This colonial expansion across the globe is called imperialism. Imperialism is the control of territory already occupied and organized by an indigenous society.

State Formation and the Centralization of Power

Today we take it for granted that different societies are governed by different states, but this has not always been the case. Since the late nineteenth century, virtually the entirety of the world’s inhabitable land has been parceled up into areas with more or less definite borders claimed by various states. Earlier, quite large land areas had been either unclaimed or uninhabited, or inhabited by nomadic peoples who were not organized as states. In fact, for most of human history, people have lived in stateless societies, characterized by a lack of concentrated authority, and the absence of significant inequalities in economic and political power.

The first known states were created in Ancient Egypt, Mesopotamia, India, China, the Americas (e.g., Aztec civilization, Inca civilization). Most agree that the earliest states emerged when agriculture and writing made it possible to centralize power durable. Agriculture allowed communities to settle and also led to class division: some people devoted all their time to food production, while others were freed to specialize in other activities, such as writing or ruling. Thus, states, as an institution, were a social invention. Political sociologists continue to debate the origins of the state and the processes of state formation.

9.2 Political Institutions of a State

There are various forms of government a country can adopt and how government forms the foundations of the institutions that countries build. Although this course tries to give a global perspective on government, a lot of the specifics we will look at will be from the perspective of the United States.

Divisions of Power

How do societies remain free? Constitutions, as we have seen, can declare there are all kinds of freedoms. For them to work, people have to obey the law. One answer has been dividing power within a government, so that there are checks on the power of any one part of the government, or the power of any particular interest group. If the power of the government is limited, citizens see that government is not overstepping its bounds, and are more likely to go along and obey the law.

The power within a government can be divided in various ways. Obviously, in authoritarian governments, power is not divided, and so there is no check on the power of whoever has the authority. This can create a couple of problems. First, it robs people of the ability to peacefully take action if the government does something they do not like. Second, there are no brakes if the government gets carried away – nothing in the system that could force those in authority to adhere to the laws as written.

Checks on power begin with elections. Elections effectively split power between the people and the government. If citizens do not like something government is doing, they can vote elected leaders out of office. However, elections are periodic – they only happen every so often – and in the short term, the government can do things that an election will take too long to rectify.

A second check on power is the division of power into different branches. This is not very common around the world; many republics tend to concentrate power in the legislative branch. That is especially true of parliamentary systems, where the head of government, the prime minister, is usually the leader of the majority party in parliament. So in that system, there is no separate branch that checks the power of parliament (except, perhaps, a constitutional court that can rule on the constitutionality of a particular law). This is called legislative supremacy – most power in the government rests with the legislative body. It has the advantage of letting things happen more quickly. In a parliamentary system, a new majority party can make changes more quickly, as there is no president to veto new laws, or usually even another legislative chamber where proposed changes can bog down.

That happens in a country such as the United States, where power is divided between co-equal branches of government. In the case of the U.S., that means only Congress can pass laws; the president must sign them to become law, and the court system can declare laws to be unconstitutional and thereby null and void. Of course, the president appoints federal judges, who must be confirmed by the U.S. Senate, and Congress as a whole can impeach and remove any federal official from office for “high crimes and misdemeanors.” The problem with this term is that the Founding Fathers never clarified what “misdemeanors” constituted a big enough crime to remove a sitting president from office. The ancient Roman Republic had even more checks on power, to the point where needed reforms were impossible to push through because somebody nearly always had the power to keep them from happening. The American government can sometimes look that way, although when the game is on the line, the system does allow change to happen, such as the passage of civil rights laws in the 1960s. On the other hand, it took nearly 100 years after the Civil War for the question of civil rights to be meaningfully addressed. Consequently, division of power into branches is both a prize and a penalty in government. The checks and balances inherent in such a division make it harder for government to get carried away, and also make it harder to get anything done.

Unitary and Federal States

Most governments are placed into two categories: federal states or unitary states. Unitary states place most of the political power in the hands of a central government. The unitary state model works best with states that have little cultural or ethnic diversity and strengthen national unity. The United Kingdom is an example of a unitary state. Federal states, like the United States, works best with nations that have greater diversity. Size also determines if a government tends to be unitary or federal. Large states like the United States, Russia, or Canada tend to be federal because having the entire country controlled by one city (i.e., capital) becomes impractical. Many states around the world have been pressured to decentralize their governments and provide more political power to smaller ethnic groups.

Federalism, Unitary Systems, and Confederations

Federalism is a system of government that divides power between different levels of government. A Confederacy would give most if not all the power to states that make up the confederation, while a unitary system of government puts all the power in the hands of the central government.

The vast majority of the world’s governments are unitary. A strong central government lends power to subnational governments, who cannot make and execute policy on their own. Unitary governments can create or abolish subnational units of governments. Federal governments typically cannot. The U.S. national government, for example, cannot decide that Wyoming would be much better as a part of Montana, or that two Dakotas is just one too many.

The other choice usually is a confederation, in which a group of states is equal partners in a government. While this prevents a strong central government from dictating to its members, it also means nobody is in charge. The United States, from 1783-1788, was a confederacy, under the Articles of Confederation. It did not work very well. The national government could not pay its debts, which caused the economy to shrink; the states were on the edge of war over trade and territorial issues. The Confederate States of America seceded from the Union in 1861, leading to the Civil War. They, too, suffered the problem of being unable to compel the member states to support the war effort fully.

The European Union is a confederation. Although there is a freely elected European Parliament, it lacks the full authority to force the 27 member states to do everything it might. The power of the confederation primarily exists because the member nations have signed on to the treaties creating it, because they share a common currency (the Euro) and because states such as Germany and France have so much more economic power than the other members (and cannot afford to see it all fail). It helps that all the member nations are relatively well-developed states and all republics with regular elections of their own. The EU also seems to be very careful in not stepping on the sovereignty of its member nations. As a consequence, despite EU provisions that require member nations to maintain roughly balanced budgets, significant budget deficits in Greece, Italy, and Spain have provoked a financial crisis for the entire union.

imageFederalism divides and shares power between the national government (often referred to as the federal government in the U.S.) and subnational governments such as states or provinces. Subnational governments may be bound by a national constitution, but have some ability to work within that framework to create their particular laws. In U.S. federalism, for example, states can regulate trade within their borders, but only the federal government can regulate commerce that crosses state borders. National governments usually retain the sole ability to provide for national defense and the conduct of foreign relations, whereas both the states and the national government can create traffic and environmental laws. Both levels can raise revenues and spend money, while only national governments can address topics relating to international trade. Larger nations sometimes turn to federalism to manage widespread territories, such as the United States, Canada, and Australia.

Federalism comes in varies degrees. In weak federalism, states do not get very much power, as in Mexico or Brazil. In strong federalism, subnational governments have a higher degree of power, as in Canada. The federalism in the United States is somewhere in between. Worldwide, 26 states are federal republics; nine more have granted some local authority to regional governments.

For example, for most of its history, the United Kingdom was a unitary state. England conquered Wales and Ireland, and was united with Scotland when James I became king of both nations in 1603. Ireland won its independence in 1921, but the six counties of what became Northern Ireland voted to remain in the United Kingdom. However, then, in 1997, people in Scotland and Wales voted for devolution, by which the central government granted some authority to local assemblies there. Northern Ireland also now has its local assembly as well. All can raise taxes, spend money, and order their affairs, but they are not sovereign states.

9.3 Shape of States

The shape of a state is essential because it helps determine potential communication internally, military protection, access to resources, and more. The following is a list of the six types of state shapes and can be viewed in Google Maps by clicking on the links provided.

Compact states have relatively equal distances from their center to any boundary, much like a circle. They are often regarded as efficient states. An example of a compact state would be Kenya, Rwanda, Uganda, and Burundi.

Elongated states have a long and narrow shape. The major problem with these states is with internal communication, which causes isolation of towns from the capital city. Malawi, Chile, and Vietnam are examples of elongated states.

Prorupted states occur when a compact state has a portion of its boundary extending outward exceedingly more than the other portions of the boundary. Some of these types of states exist so that the citizens can have access to a specific resource such as a large body of water. In other circumstances, the extended boundary was created to separate two other nations from having a common boundary. An example of a prorupted state would be Namibia.

Perforated states have other state territories or states within them. A great example of this is Lesotho, which is a sovereign state within South Africa.

Fragmented states exist when a state is separated. Sometimes large bodies of water can fragment a state. Indonesia is an example of a fragmented state. Fragmentation also occurs when a state is separated by another state. An example in the U.S. would be Michigan.

Landlocked states lack a direct outlet to a significant body of water such as a sea or ocean. This becomes problematic specifically for exporting trade and can hinder a state’s economy. Landlocked states are most common in Africa, where the European powers divided up Africa into territories during the Berlin Conference of 1884. After these African territories gained their independence and broke into sovereign states, many became landlocked from the surrounding ocean. An example here would be Niger.

Types of State Boundaries

State boundaries are determined either by physical features such as rivers, mountains, deserts, or glaciers or by cultural features such as religion, culture, or ethnicity. Boundaries are dynamic features that vary with space and time. Throughout most of human history, boundaries were determined by frontiers where no political entity controlled the area. These were often large, uninhabitable regions such as deserts, oceans, and glaciers. However, technological and communication advancements have allowed nations to protect their regions without the need of frontiers. Today, most frontiers have been replaced by boundaries.

Desert boundaries can be quite significant barriers for states and can serve for protection. Deserts are typical along 30 degrees north or south of the equator where permanent high pressure creates sunny, dry conditions year-round.

Mountainous boundaries can also protect large areas if they are difficult to climb through. However, they can also isolate societies from each other using transportation, trade and export, and culture. Like desert boundaries, they can also make geopolitics difficult when determining the boundary of a state since it is not a clear boundary or line.

Often, water boundaries like rivers, lakes, and oceans create state boundaries. If the body of water is large enough, it can be protective. Invading armies would need to use boats and limited resources to attack a state from its water boundary. However, boundaries that use rivers and lakes can be problematic with changing climates. If a river meanders to a new location, does the boundary of that country also change?

Geometric boundaries are straight lines drawn on a map.

Cultural boundaries are used to separate people with differences in both of these cultural traits. Often, cultural and ethnic conflicts occur between people with different languages or religions. Religious differences often coincide with boundaries between states, but in only a few cases has religion been used to select the actual boundary line. The most notable example was in South Asia, when the British partitioned India into two states based on religion. The predominantly Muslim portions were allocated to Pakistan, whereas the predominantly Hindu portions became the independent state of India. Language is an essential cultural characteristic for drawing boundaries, especially in Europe. By global standards, European languages have strong literacy traditions and formal rules of grammar and spelling. Language has long been an essential means of distinguishing distinctive nationalities in Europe. In 2011, the state of Sudan separated into Sudan and South Sudan along a language boundary.

9.4 International Institutions

Even as the Cold War dragged on, the nations of the world created international forums for attempting to address disputes between nations. World War I, the war to end all wars, as it was known at the time, prompted the victors to create an international body known as the League of Nations. At its peak, it included 58 nations, and created several forums for addressing political and economic issues. It lasted from 1920 to 1942, and suffered immediately from the failure of the United States to join. The U.S. became somewhat isolationist following World War I, the end of which created only an uneven peace and seemed to foster as many problems as it solved.

Nonetheless, the league represented the high point of interwar idealism, built on a belief that nations could talk instead of shoot, and that diplomacy would solve more problems than would bombs. Despite its best intentions, it was mostly powerless, and the member nations failed to act when Italy invaded Italy unprovoked in 1935. The league effectively collapsed with the start of World War II.

Following the end of the war, however, the nations gathered to try it again, creating the United Nations in 1947. The U.N., headquartered in New York City, declared its support in its charter for a broad range of human rights, and attempted to provide a multilateral forum for talking things out. Although every member nation gets one vote, a certain number of decisions must be funneled through the 15-member Security Council, which consists of five permanent members, including the United States, France, China, the Russia Federation (formerly the Soviet Union), and the United Kingdom. The other ten members are elected by the General Assembly to two-year terms, with each region of the globe represented on the council.

The five permanent members each have veto power, and can block action by the council. Also, since the members are often taking what can only be described as a realist perspective on their approach to foreign policy, Russia may seek to block concerted action in war-torn Syria, where it has interests, just as the U.S. will block U.N. resolutions to condemn Israel’s handling of the Palestinian question. Which is, in case you have missed it, whether there will ever be a fully sovereign Palestinian state. The Security Council’s permanent membership is overwhelmingly white and western. One suggestion has been to add Brazil, India, Germany and Japan (sometimes called the G-4) as permanent members, plus perhaps one African and one Arab state. The existing permanent members have not exactly jumped on that bandwagon, as doing so would reduce their power on the council. The U.S. supports adding Japan and perhaps India; the Chinese oppose adding Japan. Great Britain and France have supported adding the entire G-4.

The U.N., through its member nations and its various branches, has had some success. Member nations have contributed combat troops for peacekeeping missions, which attempt to separate belligerent groups in one country or region to forestall all-out war. It has in fact, since its inception, negotiated 172 peace settlements that have prevented all-out war in various parts of the world. U.N.-led efforts, via the World Health Organization, to stamp out various diseases have met with some success, a few nations will object to efforts to end deadly diseases such as smallpox. U.N. cultural efforts have probably also helped preserve important historical sites all over the world, and have at least underscored the importance of preserving some of our shared past. So while the U.N. has not managed to end the war, it has not been an abject failure.

One of the essential documents that came from the United Nations is called the Declaration of Human Rights (  Based on the United States Bill of Rights, this declaration declares what rights humans have throughout the world no matter what nation they are a citizen of.

The U.N. includes the International Court of Justice, which has been used to settle disputes between nations. It has 15 justices elected from the U.N. General Assembly, and while the Security Council can enforce its decisions, council members may also veto that action. Consequently, the court has acted with mixed success. In 1984, for example, the court ruled that U.S. efforts in Nicaragua, in fact, violated international law; the U.S. ignored the decision. In other instances, the court has been able to help solve border disputes between nations. Special courts also have been established by the U.N. to try war criminals from conflicts in Rwanda and the former Yugoslavia.

Other international organizations have had some impact globally, particularly in economic areas. The World Bank and the International Monetary Fund have attempted to spur economic developments and end poverty, with decidedly mixed results. Critics abound on both the left and the right. Conservative critics say they waste too much money; liberal and left critics say it merely helps cement the economic dominance of the western world. Sometimes they fund projects that make sense, such as wastewater treatment projects around the world, while at other times, they support efforts, like digging a canal to flood a seasonal river in Africa to produce fish in the desert, manage only to produce the most expensive fish in the world. Similarly, the World Trade Organization (WTO), which is a forum for resolving trade disputes and for encouraging open trade, is neither all good nor all bad.

Not every intergovernmental organization (IGO) is global in scope. The world is peppered with regional organizations, ranging from the European Union (EU) to the African Union.

The EU is particularly noteworthy. It grew out of the end of World War II, beginning with a customs union to ease trade between Belgium, the Netherlands, and Luxembourg. From there it grew into trade agreements over coal and steel, to the European Common Market, and finally to the EU in 1993. It now has 27 member states in a political and economic union. While not quite the United States of Europe, it does have an elected parliament with the ability to make some common law for the entire group, and a common currency, the euro. Travel and trade over national borders are considerably eased, and crossing from one EU state to another is now little more complicated than crossing from one U.S. state to another.

No other intergovernmental organization is quite that extensive. For example, ASEAN, the Association of Southeast Asian Countries, has ten member states and focuses on promoting economic development and shared expertise and resources. The North Atlantic Treaty Organization (NATO) is a relic of the Cold War. Initially created to help forestall Soviet aggression in Europe, it remains a mutual defense pact between the U.S., Canada and much of Europe. An attack on one member is regarded as an attack on all, so that the U.S. response to 9.11 was in fact at NATO response.

To the extent that international institutions work at all, it is because nations adhere to what the institutions say. While a hard-line realist perspective would encourage ignoring the U.N. or the WTO, a liberal perspective would suggest that nations go along if only because it is in their interest for others to do the same. A nation cannot very well expect another nation to observe the rule of law if it does not do so itself. International law, therefore, works because of reciprocity—each state expects the others to behave the same way, so it adheres to the law to encourage others to do the same.

The United Nations

The United Nations (UN), headquartered in New York City in 1949, is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace. The UN was founded in 1945 after World War II to replace the League of Nations, to stop wars between countries, and to provide a platform for dialogue. It contains multiple subsidiary organizations to carry out its missions.

Replacing the League of Nations

The League of Nations failed to prevent World War II (1939–1945). Because of the widespread recognition that humankind could not afford a third world war, the United Nations was established to replace the flawed League of Nations in 1945. The League of Nations formally dissolved itself on April 18, 1946, and transferred its mission to the United Nations: to maintain international peace and promote cooperation in solving international economic, social, and humanitarian problems.

Creation of the United Nations

The earliest concrete plan for a new world organization was begun under the aegis of the U.S. State Department in 1939. Franklin D. Roosevelt first coined the term ‘United Nations’ as a term to describe the Allied countries. The term was first officially used on January 1, 1942, when 26 governments signed the Atlantic Charter, pledging to continue the war effort.

On April 25, 1945, the UN Conference on International Organization began in San Francisco, attended by 50 governments and several non-governmental organizations involved in drafting the United Nations Charter. The UN officially came into existence on October 24, 1945, upon ratification of the Charter by the five then-permanent members of the Security Council – France, the Republic of China, the Soviet Union, the United Kingdom, and the United States – and by a majority of the other 46 signatories. The first meetings of the General Assembly, with 51 nations represented, and the Security Council, took place in London in January 1946. Since then, the UN’s aims and activities have expanded to make it the archetypal international body in the early 21st century.

UN Peacekeeping

The United Nations Peacekeeping began in 1948. Its first mission was in the Middle East to observe and maintain the ceasefire during the 1948 Arab-Israeli War. Since then, United Nations peacekeepers have taken part in a total of 63 missions around the globe, 17 of which continue today. The peacekeeping force as a whole received the Nobel Peace Prize in 1988.

Though the term “peacekeeping” is not found in the United Nations Charter, the authorization is generally considered to lie in (or between) Chapter 6 and Chapter 7. Chapter 6 describes the Security Council’s power to investigate and mediate disputes, while Chapter 7 discusses the power to authorize economic, diplomatic, and military sanctions, as well as the use of military force, to resolve disputes. The founders of the UN envisioned that the organization would act to prevent conflicts between nations and make future wars impossible; however, the outbreak of the Cold War made peacekeeping agreements extremely difficult due to the division of the world into hostile camps. Following the end of the Cold War, there were renewed calls for the UN to become the agency for achieving world peace, and the agency’s peacekeeping dramatically increased, authorizing more missions between 1991 and 1994 than in the previous 45 years combined.

9.5 Challenges to the Nation-State

In the world in which we live, the globe is divided up into sovereign nations. Remember that a sovereign state is one in which the state in the form of the government is the highest earthly power – there is no place to appeal a decision of the state except the state itself. So a sovereign state has defined borders that are respected by its neighbors, and control over its territory. In this part of the discussion, when we use the term “the state,” we mean a sovereign nation, not a political subdivision such as a U.S. or Mexican state. States in federal systems such as the U.S. and Mexico are formally referred to as sovereign states, but they are still ultimately dominated by national governments.

Moreover, this is where the challenges of international relations begin. In much of our discussion of politics, it is presumed that the state holds power and uses it as the people who control the state see fit. The power may be divided into different branches and levels of government, or not divided; through mechanisms such as elections, different people may assume power and state policies may change as a result of those elections. This presumption of a kind of state and a kind of allocation of power casts the study and practice of politics in a particular light. There is a way to resolve disputes; ultimately, somebody has the power to say yes or no and, absent violent revolution; everybody has to go along. However, in a world of genuinely sovereign states, which recognize no higher authority than themselves, the system is best described as anarchy.

A sovereign state is said to be the ultimate authority within its boundaries, borders that are respected by its neighbors. The government is legitimate in the eyes of the citizens, who generally obey the law. The United States is a sovereign nation; so are France and Indonesia. Most of the 192 recognized nations on earth are, in fact, sovereign nations.

Somalia, on the east coast of Africa, is not quite. The nation is currently divided into three parts. First is the former legitimate government of Somalia, which controls very little of the country, mostly in the south, and is beset by various warlords and religious factions. In the middle is a functioning state calling itself Puntland, which does not seek independence from Somalia but, at this point, might as well be. In the north is a state calling itself Somaliland, which is mainly functioning as a sovereign nation although few other countries currently recognize it as such.

This world of sovereign states came together in a treaty called the Peace of Westphalia in 1648. That treaty ended the 30 Years War, literally a three-decade-long conflict between Catholic and Protestant rulers and their subjects that tore apart what is now Germany and caused widespread suffering across Europe. Throughout history, people have found creative and largely pointless reasons for killing each other. However, the upshot of the treaty was that states had a right to order their affairs, in this case, the most northern, Protestant principalities of Germany and what was then called the Holy Roman Empire. The treaty, in effect, created the notion of sovereignty as an acknowledged fact of international law and diplomacy, and the Europeans exported the idea from there to the rest of the world.

European colonialism, as when the European nation states carved up Africa at the end of the 1800s, forced sovereignty onto sometimes disparate groups of people that had previously been more or less sovereign nations in their parts of the continent. Only two African states – Liberia, which which had been carved out earlier in the century by freed American slaves, and Ethiopia, which had been successfully fending off invaders for a thousand years—survived the onslaught. Although Africa had long been home to several substantial kingdoms and empires, the Europeans by the late 1800s had taken a technological leap forward that allowed them to conquer the continent in a few decades. The redrawing of the African map lumped together with groups of people who had previously been part of different states, creating political challenges when the Europeans were forced out after World War II.

A world comprising sovereign states means that there is no overarching world power that can tell them what to do. Why not, then, a world government to sort everything out? First, most if not all the sovereign states would have to agree, and both political leaders and ordinary citizens tend to dislike having someone else tell them what to do. The farther away from that someone is, the less they like it. Visions of black helicopters and invading U.N. troops were the stuff of many Americans’ paranoid nightmares in the 1970s and 1980s, despite the lack of any reality to this fear. Even if such a government could be established, the variety and diversity of the world would make it very difficult to rule, even in a highly democratic state. A world government would have to keep control and settle local and regional disputes, becoming, in the process, as despotic as the states it replaces, if not more so.

So, what we are left with are a lot of sovereign states, and a world system that is based on that single fact. Moreover, as there is no referee or overarching power, one state can erase another, as when Prussia and Russia effectively erased Poland, once the most significant state in Europe, from the map in 1795. The Poles, and their language, culture, and traditions remained, but the Polish state did not reappear until 1918. This does not mean that a state can act without consequence. When Iraq invaded Kuwait in 1990, states from around the world united in the effort to drive the Iraqis out and re-establish Kuwaiti sovereignty. Later in the same decade, Europeans and Americans joined to end ethnic cleansing in what was then Yugoslavia. So no state operates in a vacuum.

What remained of Poland after its 18th-century partition, and what most defines a place such as Somalia today, is a nation. In the precise terminology of international relations, a state has defined borders, but a nation has a cultural, linguistic, or ethnic similarity among a group of people. A nation is a sense of community among a group of people; that group of people may want to control themselves politically and become a nation as well. So, for example, the Kurds, of whom around 30 million live in the Middle East, are a nation but not a state. They are divided chiefly between Turkey, Iraq, Syria, Iran, comprising the largest single ethnic group in the world without its state. Kurdish separatists have fought for independence in Turkey, and all but carved out a sovereign state in the north of Iraq. However, at the moment, the Kurds remain a nation, and not quite a state.

9.6 Terrorism

The term terrorist (Latin for “to frighten”) has become a mainstream term since the attacks of September 11, 2001, in New York, Virginia, and Pennsylvania. Terrorism is the systematic use of violence by a group in order to intimidate ordinary citizens as a way to coerce a government into granting the group’s demands. Violence is considered necessary by terrorists to bring widespread publicity to goals and grievances that they believe cannot be addressed through peaceful means.  Belief in the cause is so strong that terrorists do not hesitate to strike despite knowing they will probably die in the act. State-sponsored terrorism exists when a state provides sanctuary for terrorists that are wanted by other countries; provides weapons, money, and intelligence to terrorist groups; or helps in planning a terrorist attack.

Geospatial technology is used heavily in geopolitical conflicts within the National Geospatial-Intelligence Agency, National Security Agency, and the Department of Homeland Security, to name a few. The video on the right is a section of the Geospatial Revolution, Episode 3 that focuses on war and conflict.

Click here to read an interesting article from WIRED Magazine titled How Geospatial Analytics is Helping Hunt the LRA and al-Shabaab.

Geospatial technology can also be used for humanitarian efforts as a way to end conflict or monitor situations before they escalate. One organization, called the Satellite Sentinal Project, was created by The Enough Project and the largest private satellite imagery corporation called Digital Globe. The organization was first used satellite imagery from Digital Globe and Google Earth to monitor potential humanitarian conflicts along the border of Sudan and the newly created South Sudan. Now it is using satellite imagery to track poachers who use the money from the black market to fund civil wars like the Lord’s Resistance Army (LRA).

Chapter 10 Economic Geography: Agriculture and food for print only


10.1: The Roots of Agriculture

The traditional story about agriculture goes something like this: initially, people were hunter-gatherers who lived short lives because they had to scrounge for food from what nature provided. At some point, someone in the tribe made the discovery that people could plant crops. This led to better food supplies, less work, and more leisure time to develop higher civilization. Geographers now know that this traditional story gets it backward in many ways. Hunting and gathering is a comfortable way of life, while agriculture is often an adaptation of necessity with significant negative ramifications.

To start, we need to define “agriculture.” The traditional story proposes that there is a significant leap forward – sometimes called the “agricultural revolution” or “Neolithic revolution” – when societies invent agriculture. However, it is more accurate to see agriculture as one stage on a continuum of intensification. Intensification refers to the amount of production per unit of land that is extracted for human use. Raising the level of intensification practiced by society requires increased manipulation of natural processes by humans. We can imagine a scale of intensification running from a wilderness where the only human activity is hikers picking a few berries to eat on their way, to a modern industrial farm that mass-produces corn.

Hunter-gatherers do not merely wander the landscape, picking up whatever food and other resources they happen across. Hunter-gatherer societies have the sophisticated knowledge of the plants and animals found in their territory, and when and how they can be harvested. While they are somewhat at the mercy of the earth’s cycles and the bioclimatic zone in which they live, hunter-gatherers do not just wait for nature to provide them with resources. Instead, they are astute observers of weather and the seasonal migration patterns of animals and growth patterns of plants, and they may deliberately manipulate the environment to encourage the production of the plants and animals they want.

Agriculture is defined as the cultivation of crops and efforts to breed better strains. Cultivate means “to care for,” and a crop is any plant cultivated by people. If society continues to increase its level of intensification, eventually it will find itself practicing types of production that we would recognize as agriculture. This is what occurred in different regions dating from 10,000 to 8,000 BC in the Fertile Crescent and perhaps 8000 BC in the Kuk Early Agricultural Site of Melanesia. There are various debates within the scientific community between human geographers, sociologists, and anthropologists as to why agriculture arose throughout these various locations, called hearths, around the world. Despite the debate, in each hearth area, the transition from a largely nomadic hunter-gatherer way of life to a more settled, agrarian-based one, included not just the cultivation and domestication of plants, but also the domestication of animals.

Figure 10.1 Map showing centers of origin of agriculture and its spread: the Fertile Crescent (11,000 BP), the Yangtze and Yellow River basins (9,000 BP) and the New Guinea Highlands (9,000–6,000 BP), Central Mexico (5,000–4,000–3,000 BP) by Joey Row (CC BY)

We can make some general assumptions that the cultivation of plants and domestication of animals was because of environmental or cultural push factors. It was likely a combination of both, since a variety of agricultural hearths were grown around the world and under different circumstances. From a climate science perspective, the likely catalyst of agriculture was that around 10,000 years ago, the earth was shifting away from the Pleistocene Ice Age and into a warming period called an interglacial period.

Still, the question lingers: why would a society intensify to the point of developing agriculture? Agriculture increases the output of food per unit of land. Farmers can get more food and other resources, and hence support more people, out of a given chunk of land than hunter-gatherers can. Agriculture is thus associated with a boom in population. However, if a population declines, a society may de-intensify to hunting and gathering.

10.2 Types of agriculture

Today, there are two divisions of agriculture, subsistence and commercial, which roughly correspond to the less developed and more developed regions. One of the most significant divisions between more and less developed regions is the way people obtain the food they need to survive. Most people in less developed countries are farmers, producing the food they and their families need to survive. In contrast, fewer than 5 percent of the people in North America are farmers. These farmers can produce enough to feed the remaining inhabitants of North America and to produce a substantial surplus.

Subsistence agriculture is the production of food primarily for consumption by the farmer and mostly found in less developed countries. In subsistence agriculture, small-scale farming is primarily grown for consumption by the farmer and their family. Sometimes if there is a surplus of food, it might be sold, but that is not common. In commercial agriculture, the primary objective is to make a profit.

The most abundant type of agriculture practiced around the world is intensive subsistence agriculture, which is highly dependent on animal power, and is commonly practiced in the humid, tropical regions of the world. This type of farming is evidenced by significant efforts to adapt the landscape to increase food production. As the word implies, this form of subsistence agriculture is highly labor intensive on the farmer using limited space and limited waste. This is a widespread practice in East Asia, South Asia, and Southeast Asia where population densities are high, and land use is limited. The most common form is wet rice fields, but could also include non-wet rice fields like wheat and barley. In sunny locations and long growing seasons, farmers may be able to efficiently get two harvests per year from a single field, a method called double cropping.

Another form of subsistence agriculture is called shifting cultivation because the farmers shift around to new locations every few years to farm new land. Farming a patch of land tends to deplete its fertility and land that is highly productive after it is first cleared, loses its productivity throughout several harvests. In the first agricultural revolution, shifting cultivation was a common method of farming.

There are two processes in shifting cultivation: 1) farmers must remove and burn the earth in a manner called slash-and-burn agriculture where slashing the land clears space, while burning the natural vegetation fertilizes the soil, and 2) farmers can only grow their crops on the cleared land for 2-3 years until the soil is depleted of its nutrients then they must move on and remove a new area of the earth; they may return to the previous location after 5-20 years after the natural vegetation has regrown. The most common crops grown in shifting cultivation are corn, millet, and sugarcane. Another cultural trait of LDCs is that subsistence farmers do not own the land; instead, the village chief or council controls the earth. Slash-and-burn agriculture has been a significant contributor to deforestation around the world. To address deforestation and the protection of species, humans need to address root issues such as poverty and hunger.

Pastoral nomadism is similar to subsistence agriculture except that the focus is on domesticated animals rather than crops. Most pastoral nomads exist in arid regions such as the Middle East and Northern Africa because the climate is too dry for subsistence agriculture. The primary purpose of raising animals is to provide milk, clothing, and tents. What is interesting with pastoral nomads is that most do not slaughter their herds for meat; most eat grains by trading milk and clothing for grain with local farmers.

The type of animals chosen by nomads is highly dependent on the culture of the region, the prestige of animals, and the climate. Camels can carry heavy cargo and travel great distances with very little water; a significant benefit in arid regions. Goats require more water, but can eat a wider variety of food than the camel.

Most probably believe that nomads wander randomly throughout the area in search of water, but this is far from the truth. Instead, pastoral nomads are very aware of their territory. Each group controls a specific area and will rarely invade another area. Each area tends to be large enough to contain enough water and foliage for survival. Some nomad groups migrate seasonally between mountainous and low-lying regions; a process called transhumance.

The second agricultural revolution coincided with the Industrial Revolution; it was a revolution that would move agriculture beyond subsistence to generate the kinds of surpluses needed to feed thousands of people working in factories instead of in agricultural fields. Innovations in farming techniques and machinery that occurred in the late 1800s and early 1900s led to better diets, longer life expectancy, and helped sustain the second agricultural revolution. The railroad helped move agriculture into new regions, such as the United States Great Plains. Geographer John Hudson traced the major role railroads, and agriculture played in changing the landscape of that region from open prairie to individual farmsteads. Later, the internal combustible engine made possible the mechanization of machinery and the invention of tractors, combines, and a multitude of large farm equipment. New banking and lending practices helped farmers afford new equipment. In the 1800s, Johann Heinrich von Thünen (1983-1850) experienced the second agricultural revolution firsthand— because of which he developed his model (the Von Thünen Model), which is often described as the first effort to analyze the spatial character of economic activity. This was the birth of commercial agriculture.

More developed nations tend to have commercial agriculture with a goal to produce food for sale in the global marketplace called agribusiness. The food in commercial agriculture is also rarely sold directly to the consumer; rather, it is sold to a food-processing company where it is processed into a product. This includes produce and food products.

An interesting difference between emerging countries and most developed countries (MDC) regarding agriculture is the percent of the workforce that farm. In emerging countries, it is not uncommon that over half of the workforce are subsistence farmers. In MDCs like the United States, the workforce that is farmers are far fewer than half. In the United States alone, less than 2 percent of the workforce are farmers, yet have the knowledge, skills, and technology to feed the entire nation.

One of the reasons why only 2 percent of the United States workforce can feed the entire nation has to do with machinery, which can harvest crops at a large scale and very quickly. MDCs also have access to transportation networks to provide perishable foods like dairy long distances in a short amount of time. Commercial farmers rely on the latest scientific improvements to generate higher yields, including crop rotation, herbicides and fertilizers, and hybrid plants and animal breeds.

Another form of commercial agriculture found in warm, tropical climates, are plantations. A plantation is a large-scale farm that usually focuses on the production of a single crop such as tobacco, coffee, tea, sugar cane, rubber, and cotton, to name a few. These forms of farming are commonly found in LDCs but often owned by corporations in MDCs. Plantations also tend to import workers and provide food, water, and shelter necessities for workers to live there year-round.

There has always been a delicate balance between how much of the Earth’s surface can be used for agriculture and the ability to produce enough food to sustain a growing population. Climate, terrain, groundwater, and soil composition create limits on what and where crops can be produced without major human adaptations to the landscape. New technologies and scientific knowledge have helped to increase the world’s cultivated land significantly. However, spatial variations in land resources like rainfall and temperature zones are still the most significant factors in determining what land is suitable for specific crops and types of agriculture.

10.3 Agricultural regions

The world’s cultivated land has grown by 12 percent over the last 50 years, mostly at the expense of forest, wetland and grassland habitats. At the same time, the global irrigated land has doubled. The distribution of these land and water assets is unequal among countries. Although only a small part of the world’s land and water is used for crop production, most of the easily accessible and (thus economic) resources are under cultivation or have other ecologically and economically valuable uses. Therefore, the ability to expand more cultivated land is limited. Only parts of South America and sub-Saharan Africa still offer a scope for some expansion. At the same time, competition for water resources has also been growing to the extent that today, more than 40 percent of the world’s rural population is now living in water-scarce regions.

The total global land area is 13.2 billion hectares (ha). A hectare is a metric system area unit and widely used land measurement for agriculture and forestry; it equals to 10,000 square meters. Of this, 12 percent (1.6 billion ha) is currently in use for cultivation of crops, 28 percent (3.7 billion ha) is under forest, and 35 percent (4.6 billion ha) comprises grasslands and woodland ecosystems. Low-income countries cover about 22 percent of the land area, but they account for 38 percent of the global population.

Land use varies with climatic and soil conditions and human influences (Figure 10.12). Figure 10.13 further shows the dominant land use by region. Deserts prevail across much of the lower northern latitudes of Africa and Asia. Dense forests predominate in the heartlands of South America, along with the seaboards of North America, and across Canada, Northern Europe and much of Russia, as well as in the tropical belts of Central Africa and Southeast Asia. Cultivated land is 12 to 15 percent of the total land in each category.

Cultivated land is a leading land use (a fifth or more of the land area) in South and Southeast Asia, Western and Central Europe, and Central America and the Caribbean, but is less critical in sub-Saharan and Northern Africa, where cultivation covers less than a tenth of the area. In low-income countries, soils are often more deficient, and only 28 percent of the total cultivated land is suitable for high yield crops.

imageIt is also important to note that with overall growth in cultivated land, rain-fed croplands have declined slightly and irrigated cropland has more than doubled in the time between 1961-2008. This helps us to understand how humans have adapted the landscape for agricultural purposes.

Water resources available for irrigation are very unevenly distributed, with some countries having an abundance of water while others live in conditions of extreme scarcity or shortage of water. Also, even where water may appear abundant, much of it is not accessible or is very expensive to develop, or is not close to lands that can be developed for agriculture. Water scarcity has three dimensions: physical (when the available supply does not satisfy the demand), infrastructural (when the infrastructure in place does not allow for satisfaction of water demand by all users) and institutional (when institutions and legislation fail to ensure reliable, secure and equitable supply of water to users).

Evolution of land under irrigated and rainfed cropping (1961–2008) (FA-SOLAW)

In some regions, particularly in the Middle East, Northern Africa, and Central Asia, countries are already using water resources more than what is available. The resultant stresses on ecosystems are increasingly apparent. It is now estimated that more than 40 percent of the world’s rural population lives in river basins that are, physically water, scarce.

Table 10.1: Types of Rainfed Production Systems and Regions

System Characteristics and Examples
Rain-fed agriculture: highlands  Low productivity, small-scale subsistence (low- input) agriculture; a variety of crops on small plots plus few animals.
Rain-fed agriculture: dry tropics Drought-resistant cereals such as maize, sorghum, and millet. Livestock often consists of goats and sheep, especially in the Sudano-Sahelian zone of Africa, and in India. Cattle are more widespread in southern Africa and Latin America.
Rain-fed agriculture: humid tropics Mainly root crops, bananas, sugar cane, and notably soybean in Latin America and Asia. Maize is the most important cereal. Sheep and goats are often raised by more impoverished farmers while cattle are held by wealthier ones.
Rain-fed agriculture: subtropics Wheat (the essential cereal), fruits (e.g., grapes and citrus), and oil crops (e.g., olives). Cattle are the most dominant livestock. Goats are also essential in the southern Mediterranean, while pigs are dominant in China and sheep in Australia.
Rain-fed agriculture: temperate Principal crops include wheat, maize, barley, rapeseed, sugar beet, and potatoes. In the industrialized countries of Western Europe, the United States and Canada, this agricultural system is highly productive and often combined with intensive, penned livestock (mainly pigs, chickens, and cattle).

At the same time, in more developed countries, urban and industrial demand, has been growing faster than agricultural demand. Whereas in less-developed countries agricultural use remains dominant, in Europe 55 percent of water is used by industry. Water stresses occur locally across the globe, but some entire regions are highly stressed, particularly the Middle East, the Indian subcontinent, and northeastern China. Sub-Saharan Africa and the Americas experience lower levels of water stress. The quality of water is also impacted when run-off returns to the environment. In general, increasing population and economic growth combined with little or no water treatment have led to more negative impacts on water quality. Agriculture, as the largest water user, is a significant contributor. Key pollutions include nutrients and pesticides derived from crop and livestock management.

Rain-fed agriculture depends on rainfall for crop production, with no permanent source of irrigation. Rain-fed agriculture produces about 60 percent of global crop output in a wide variety of production systems (Table 10.1). The most productive systems are concentrated in temperate zones of Europe, followed by Northern America, and rain-fed systems in the subtropics and humid tropics. Rain-fed cropping in highland areas and the dry tropics tend to be relatively low- yielding, and is often associated with subsistence farming systems. Evidence from farms worldwide shows that less than 30 percent of rainfall is used by plants in the process of cultivation. The rest evaporates into the atmosphere, percolates to groundwater or contributes to river runoff.

Agricultural Economics

We know that climate and terrain place physical limits on what can be grown in specific locations on Earth. However, we must also take into account the geographic nature of the choices farmers make when deciding what to plant. Once subsistence farming intensifies to the point of producing more food than it requires to feed a family or local community, it makes financial sense for farmers to sell their excess products. In this shift from substance to commercial agriculture farms need to be profitable; and the more profitable, the better, so farmers carefully choose the crops and animals they raise. These decisions, in turn, affect what we eat.

You might be thinking, “Farmers do not control what I eat. I eat what tastes good”, but opinions vary wildly on the issue of taste preference from country to country, and even within the countries. Taste preferences for food vary within and across ethnicities, and even house to house among people that would seem alike in almost every way. Still, some trends characterize regions, in the US, and around the world, many of these foodways have roots in the local geography of a place. It is often said, “you are what you eat,” but geographers might add the rejoinder “what you eat depends on where you eat.” Family traditions determine what people eat, but understanding the evolution of those traditions requires an analysis of the spatial contexts in which they evolved.

Our ethnic heritage explains much of our taste preferences. European immigrants to the US established most American foodways. Europeans living 300 years ago would have readily recognized many American dietary staples, such as beef, pork, chicken, bread, pasta, cheese, and milk, as well as a number of the fruits and vegetables we commonly eat. Modern Americans also copy foodways borrowed from the indigenous people of the Americas. Less prominent elements of American’s diet are traceable to Asia and Africa.

Eating is a daily ritual, and as such, it is a deeply ingrained cultural routine. What you like to eat is probably not that different from what your parents and grandparents like to eat. The same was true for your grandparents, giving dietary habits exceptional staying power. This fact is part of the reason behind our obesity crisis. Our lifestyle has changed as rapidly as technology, and the economy has evolved, but many of our foodways are stubbornly resistant to change. The diets that served our ancestors who were farmers or laborers engaged in strenuous daily activities, provides too many calories and fat for a generation working and living in the information age. Cultural lag is the term that describes the inability of cultural practices to keep pace with changes in technological advancement. Numerous behaviors exhibit cultural lag, and culturally conservative regions exhibit a higher degree of cultural lag than places with more progressive tendencies

A sizeable portion of the American diet is purely American. We have adopted several foodstuffs favored by Native Americans. Maize, better known in America as “corn,” is perhaps the most American part of our diet. Domesticated by the indigenous people of Mexico thousands of years ago, it has proven a versatile and hardy plant. It is so versatile that today much of the world eats maize in some fashion. Most Americans know maize mostly as sweet corn. Americans eat sweet corn like corn on the cob, but also canned, frozen and fresh “off the cob,” and in a variety of dishes.

Less well known are maize varieties are known as field corn, although it is far more common because of its great versatility. Field corn is too hard to eat raw, so we modify it. Some of it is processed into cornmeal or cornstarch, which we in turn use to make things like corn chips, tortillas, and sauces. We also consume a lot of corn syrup and high fructose corn syrup (HFCS) made from field corn. Corn syrups are used as a sweetener, thickeners, and to keep foods moist or fresh. HFCS is an inexpensive replacement for cane and beet sugars, and therefore is the most common sweetener used in processed foods and soft drinks.

10.4 Making Sense of Land Use

Geographers are concerned with understanding why things happen in geographical spaces. Johann Heinrich von Thünen (1783-1850) was a farmer on the north German plain, and he developed the foundation of rural land use theory. Because he was a keen observer of the landscape around him, he noticed that similar plots of land in different locations were often used for very different purposes. He concluded that these differences in land use between plots with similar physical characteristics might be the result of differences in location relative to the market. Thus, he went about trying to determine the role that distance from markets plays in creating rural land-use patterns. He was interested in finding laws that govern the interactions between agricultural prices, distance, and land use as farmers sought to make the greatest profit possible.

The von Thünen model is focused on how agricultural is distributed around a city in concentric circles. The dot represents a city, and the first ring (white) is dedicated to market gardening and fresh milk production. That is because of milk products and garden crops, such as lettuce, spoil quickly. Remember that at the time von Thünen developed this model, there was no refrigeration, so it was necessary to get perishable produce to the market immediately. Because of this, producers of perishable crops were willing to outbid producers of less perishable crops to gain access to the land closest to the market. This means that land close to the community created a higher level of economic rent.

Johann Heinrich von Thünen’s model of agricultural distribution around a city in concentric circles (Wikimedia, Public Domain)

The second ring, von Thünen believed, would be dedicated to the production and harvest of forest products. This was because, in the early 19th century, people used wood for building, cooking, and heating. Wood is bulky and heavy and therefore difficult to transport. Still, it is not nearly as perishable as milk or fresh vegetables. For those reasons, von Thünen reasoned that wood producers would bid more for the second ring of land around the market center than all other producers of food and fiber, except for those engaged in the production of milk and fresh vegetables.

The third ring, von Thünen believed, would be dedicated to crop rotation systems. In his time, rye was the most important cash grain crop. Inside the third ring, however, von Thünen believed there would be differences in the intensity of cultivation. Because the cost of gaining access to the land (rent) drops with distance from the city, those farming at the other edges of the ring would find that lower rents would offset increased transportation costs. Moreover, because those farming the outer edges would pay less rent, the level of input they could invest prior to reaching the point of decreasing marginal returns (the term “marginal returns” refers to changes in production relative to changes in input), would be at a lower level than would be the case for those paying higher rent to be closer to the market. Therefore, they would not farm as intensely as those working land closer to the urban center.

The fourth ring would be dedicated to livestock ranching. Von Thünen reasoned that unlike perishable or bulky items, animals could be walked to the market. Additionally, products such as wool, hide, horn, and so on could be transported easily without concern about spoilage.

In von Thünen’ s model, wilderness bounded the outer margins of von Thünen’ s Isolated state. These lands, he argued, would eventually develop rent value, as the population of the state increased. Thus, in this fundamental theory, the only variable was the distance from the market.

Von Thünen was a farmer, and as such, he understood that his model did not exist in the whole of the real world. He developed it as an analytical tool that could be manipulated to explain rural land-use patterns in a world of multiple variables. To do this, Von Thünen relaxed his original assumptions, one at a time, to understand the role of each variable.

One of the more stringent assumptions in the Von Thünen model was his assumption that all parts of the state would have equal access to all other parts of the nation (with distance being the only variable allowed). He knew that this did not represent reality because already in his time, some roads were better than others, railways existed, and navigable water routes significantly reduced the friction of distance between the places they served. Therefore, he introduced a navigable waterway into his model, and found that because produce would be hauled to docks on the stream for transport, each zone of production would elongate along the stream.

Von Thünen model, left – modified by a river, right by George Van Otten and Dennis Bellafiore (https://www.e-

Von Thünen also considered what would happen if he relaxed his assumption that production costs were equal in all ways except for the costs associated with distance from the market. Eventually, as he worked with his model, he began to consider the effects of differences in climates, topography, soils, and labor. Each of these could serve to benefit or restrict production in a given place. For example, lower wages might offset the advantages realized by being near a market. The difference in the soil might also offset the advances of being close to the market. Thus, a farmer located some distance from the market with access to well-drained, well-watered land with excellent soil, and low-cost labor nearby, might be willing to pay higher rent for the property in question even if it were a bit further from the market than another piece of land that did not have such amenities.

Von Thünen’s concentric circles were the result of the limits he imposed on his model in order to remove all influences except for distance. Once real-world influences are allowed to invade the model, the concentric land-use pattern does not remain in place. Modern technology, such as advances in transportation systems, increasingly complicates the basic concentric circle model. Recent changes, like the demand for agricultural products, also influence land-use patterns.

Changes in demand for farm products often have dramatic impacts on land uses. For example, when fuel production companies demanded dramatically increased quantities of corn to produce ethanol, and the price of corn rose accordingly, farmers responded by shifting from other food crops to ethanol-producing corn. As a result, land well suited for corn production now sells at premium prices (in Iowa and other corn-producing states, an acre of farmland may bring $12,000.00 or more). Currently, there is little extra farmland available upon which an expansion might take place. Therefore, changes in demand typically result in farmers shifting to crops that will bring the highest return.

The mid-Willamette Valley of Oregon provides another example of how changes in demand affect agricultural land uses. For years, the mid-Willamette Valley was the site of many medium-sized grain farms. The primary grain crops included wheat, barley, oats, Austrian peas, and clover. Also, farmers in the region produced row crops, orchard crops, hay, and grass seed. During the 1970s, in response to increasing demand, the price of grass seed increased dramatically. As a result, Willamette Valley farmers quickly changed their focus from the production of grain to grass seed. Soon after, several grain processing facilities closed, and grass seed cleaning, storage, and market facilities opened. There were other unexpected impacts, as well. For example, Willamette Valley grain farms once provided excellent habitat for Chinese pheasants. Pheasants eat grain, but they do not eat grass seed. When the grain fields disappeared, so, too, did the pheasants.

Like pheasants, people do not eat grass seed. On the other hand, oats, wheat, and barley are all food crops. Once a nation can meet its basic food needs, agriculture can meet other demands, such as the demand for Kentucky bluegrass for use on golf courses, lawns, and other landscaping. As incomes go up, the demand for food crops will grow proportionately. Eventually, however, when the demand for food is satiated, subsequent increases in income will no longer bring corresponding increases in the demand for food. This is the result of the elasticity of demand relative to changes in income. The measure of elasticity of demand is calculated by noting the amount of increase in demand for an item that a unit of increase in income generates. For example, luxury products such as expensive wines have a high elasticity of demand, whereas more common items such as rice have a low elasticity of demand. Once a family has all the rice they can typically eat, it will not purchase more as a result of more income. More income, however, would likely bring an increase in the consumption of prime cuts of beef or other such luxury foods.

New technologies in transportation, agricultural production, and the processing of food and fiber often have substantial impacts on the use of rural land. Technological changes mainly influence transportation. For example, the construction of the rail lines that connected the Midwestern United States with the market centers of the East made it possible for farmers in Iowa, Illinois, and other prairie states to improve their profits by feeding the corn they grew to hogs which they then shipped to the markets in the east. This is because the value of a pound of pork has always been far greater than the value of a pound of corn. Thus, by feeding the corn to the hogs, and then shipping the hogs, the farmers could earn greater profits because the shipping costs of their product were lower. In a sense, the farmers were selling corn on the hoof. Without easy access to railheads, this profitable agricultural scheme would not have been possible.

Of course, some folks have specialized in selling corn after it has been distilled into a liquid form. When the sale of alcohol was illegal in the USA, the transport of “liquid corn” was made easier when, in 1932, Henry Ford introduced the Ford V8, thereby enabling “Moonshiners” to move their product from hidden distilleries to waiting markets without being caught by the police. Additionally, “moonshiners” became expert mechanics who could turn a standard 60 horsepower V8 into a powerful, fast, agile machine. People who specialized in modifying these stock cars became pioneers in NASCAR racing.

Over the years, improvements in technologies have tended to drive down the relative costs associated with shipping farm produce. Furthermore, inventions such as refrigerated rail cars and trucks have eliminated some of the land- use constraints that once limited the locational choices of farmers who produced perishable goods. Less expensive haulage costs, decreased transit times, and better handling and processing methods have all served to make transportation systems more efficient and, hence, less expensive.

In theory, this should serve to reduce the importance of distance relative to other non-distance factors. Consider how far from the market a producer of fresh vegetables could locate in the early 19th century. The lack of all-weather roads and reliance on the transportation conveyances of the time (human and animal power) dictated a production location within a few miles of the market. The creation of all-weather roads that could be traversed by a horse and wagon, however, changed the situation. Without the roads, fresh vegetable growers would have been forced to pay high prices for land very near the market. With the roads, they were able to use less expensive land and still get their crops to market before spoilage made it impossible to sell them.

If the creation of an all-weather road made such a difference in land uses, imagine the impacts of the refrigerated aircraft now used to deliver loads of fresh flowers. Currently, many of the fresh flowers sold in US supermarkets come to the United States from the Netherlands via giant jet transport aircraft. This technology has significantly altered the importance of distance relative to the production of fresh flowers.

10.5 Population and Food Production

Recall that English economist Thomas Malthus (1766-1834) proposed that the world rate of population growth was far outrunning the development of food supplies. Malthus proposed that the human population was growing exponentially, while food production was growing linearly. Below is an example:

During Malthus’s time, only a few relatively wealthy countries had entered Stage 2 of the demographic transition model high population growth. He failed to anticipate that relatively emerging countries would have the most rapid population growth because of a medical revolution. Many social scientists and even environmentalists are strong supporters of Malthus’s hypothesis of the coming global food shortage and are taking it several steps further. Human population growth and consumption may be outstripping a wide variety of the earth’s natural resources, not just food production. Billions of people may soon be engaged in a search for food, water, energy, and resources. These days, technology is allowing us to convert food into a fuel called ethanol. In the United States, large amounts of corn are being used to create biofuel as a way to remove ourselves from our addiction to oil. This has caused global corn prices to rise dramatically. Wars and civil violence will increase in the coming years because of scarcities.

Others discredit Malthus because his hypothesis is based on the world supply of resources being fixed rather than flexible and expanding. Technology may enable societies to be more efficient with scarce resources or allow for the use of new resources that were once not feasible. Some believe population growth is not a bad thing either. A large population could stimulate economic growth and, therefore, the production of food.

Marxists believe that there is no direct connection between human population growth and economic development within an area. Social constructs of hunger and poverty are the result of unjust social and economic power structures through globalization, rather than because of human population growth.

So even with a global community of 7 billion, food production has grown faster than the global rate of natural increase. Better growing techniques, higher-yielding, and genetically modified seeds, and better cultivation of more land have helped expand food supplies globally. However, many have noted that food production has started to slow and level off. Without new technology breakthroughs in food production, the food supply will not keep up with population growth.

The third agricultural revolution, also known as the Green Revolution, has been in response to these fears of a Malthusian food crisis. The Green Revolution consists of improvements to agriculture brought about by the application of modern scientific methods to the development of new crop varieties and agricultural inputs. The technologies of the Green Revolution first made their mark in the United States, but the term is most commonly used about their extension to farmers in developing countries.

Taking up Green Revolution technology involves adopting a whole package of inputs — improved seeds, new fertilizers, and new pesticides and herbicides, all of which have been designed to work together. The improved seeds were created through selective breeding and hybridization. The fertilizers and pesticides are composed of artificial chemicals designed to provide just the nutrients that crops need and to target their main pests and weeds. The Green Revolution produced dramatic gains in crop productivity where it was implemented, in some cases doubling or even tripling yields. Norman Borlaug, the agronomist who was the guiding force behind the Green Revolution and one of its most prominent spokespeople, was widely hailed as a hero who saved millions from starvation and won the Nobel Peace Prize.

There are many critics of the Green Revolution. While acknowledging some of the gains in the total food supply, these critics argue that the Green Revolution has several critical shortcomings. The health critiques raise concerns about whether the Green Revolution crops are safe to eat. This concern is particularly salient with respect to genetically modified organisms (GMOs). While tests have generally shown GMOs to be safe to eat, critics worry that modified organisms could trigger adverse reactions in people, for example, if a person with a peanut allergy ate corn that had a peanut gene spliced into it. There is also concern that work on improving crops has focused on boosting the size and appearance of fruits, kernels, and more, at the expense of making them less nutritious. Finally, health may be impacted by the growing style of Green Revolution crops. The Green Revolution aggressively suppresses any organism in the field that could compete with the main crop. However, for many poor farmers, “weeds” are an important supplementary source of food. Ironically, adding vitamin A to rice through genetic modification is proposed as a solution when the vitamin A deficiencies that it will fix were caused in part by a loss of leafy green “weeds” to Green Revolution herbicides.

Environmental critiques raise questions about whether Green Revolution agriculture is good for the wider environment. There are several ways in which the environment could be affected. First, the successful use of Green Revolution technology often requires increased use of water. This can deplete water supplies in dry areas (and lead to demands for environmentally-disruptive dams to increase the water supply). Pesticides, herbicides, and fertilizers frequently run off the farm into streams, with adverse effects on downstream ecosystems. Green Revolution farming can also, in some cases, pollute and deplete the soil, meaning that the gains in productivity will not be sustainable. There are also concerns about the heavy use of pesticides and herbicides, leading to the evolution of chemical-resistant super-bugs and super-weeds. Green Revolution farms can further exacerbate the problems of mono-cropping, converting large areas to farms with very low biodiversity and thus increasing susceptibility to disasters (weather-related, pest infestations, etc.). In the case of GMOs, a major worry is that modified genes will spread beyond the field. Wind and insects can carry plant pollen into neighboring non-GMO fields and non-farm areas. If the plants that receive the pollen cross-breed with the GMOs, the modified gene may become established off-farm, with potentially ecological severe consequences depending on the nature of the gene.

Social critiques center on the economic system that farmers become a part of when they adopt Green Revolution technology. Traditional agriculture was largely self- contained. Farmers produced their inputs by saving seeds from previous harvests to plant next year, by collecting their natural fertilizers, and by using their household labor to till the fields. However, the improved seeds and the package of chemical inputs that make up the Green Revolution cannot be produced on the local farm. They have to be mass-produced by large agribusiness companies and then sold to farmers. Farmers then become dependent on companies like Monsanto to buy their inputs and sell their products. The contracts that farmers sign with these companies often put small farmers at a disadvantage. Depending on the arrangements made by the farmers, they may then become highly dependent on the international agricultural market — meaning that global shifts in prices for both inputs and farm products can determine their ability to make ends meet.

An emerging trend in agriculture, which is in some ways opposed to but in other ways parallel to the Green Revolution, is the rise of organic agriculture. Organic agriculture is agriculture that avoids the use of “artificial” chemical inputs and genetically modified crops. The organics movement originated as an attempt to avoid the problems arising from the Green Revolution by creating a farming system that works in harmony with the land. This original vision of organic agriculture is reflected, for example, in community supported agriculture programs, which usually practice organic farming. In community supported agriculture, customers buy a “share” or subscription at the beginning of the growing season, then receive a portion of whatever produce the farm manages to grow. This system is meant to spread the risks of farming between farmers and consumers, create a closer bond between the farmer and consumer, and make organic agriculture more profitable. As the popularity of organic food has grown, organics have become big business. Major corporations now coordinate the production of organic ingredients all over the world. Due to the diversity of techniques and differing demands of different crops, there remains much controversy over how well organic farming achieves its goals of reducing its ecological footprint and improving consumer nutrition.

Chapter 11 Economic Geography: Industry for print only


R. Adam Dastrup, David Dorrell;Joseph Henderson; Todd Lindley;, and Georgeta Connor

11.1 Industrial Revolution

We live in a globalized world. Products are designed in one place, assembled in another from parts produced in multiple other places. These products are marketed nearly everywhere. Until a few decades ago, such a process would have been impossible. Two hundred years ago, such an idea would have been beyond comprehension. What happened to change the world in such a way. What eventually tied all the economies of the world into a global economy? Industry did. The Industrial Revolution changed the world as much as the Agricultural Revolution. Industry has made the modern lifestyle possible.

The Industrial Revolution began in England, which was by 1750, one of the wealthiest nations in the world and controlled an empire that covered one-quarter of the world’s land mass. It started with England’s textile industry, which was struggling to produce goods cheaper and faster for growing consumer markets. Making cloth, by hand, for pants, shirts, socks, bedspreads, and other domestic items had always required lots of skill and time.

As the population grew in England, more people needed textile goods. In the late 18th century, a series of innovations created by savvy businessmen and factory workers solved many of the difficulties in textile production. As the scale of production grew, the factory emerged as a centralized location where wage laborers could work on machines and raw material provided by capitalist entrepreneurs. Moreover, cotton led the way. In the 1700s, cotton textiles had many production advantages over other types of cloth. The first textile factory in Great Britain was actually for making silk, but since only wealthy people could afford the product, production remained very low. Cotton, on the other hand, was far less expensive. It was also stronger and more easily colored and washed than wool or linen.

By the late 18th century, steam power was adapted to power factory machinery, sparking an even more significant surge in the size, speed, and productivity of industrial machines. Heavy industries like ironworking were also revolutionized by new ideas, and new transportation technologies were developed to move products further and faster. Growing businesses soon outstripped the financial abilities of individuals and their families, leading to legal reforms that allowed corporations to own and operate businesses.

Nineteenth-century industrialization was closely associated with the rapid growth of European cities during the same period. Cities grew because of the influx of people desiring to take advantage of the factory jobs available in urban areas. Urbanization extended industrialization as factories were built to take advantage of urban workforces and markets.

Industrialization changed the relationship that existed between cities and their surrounding rural areas. In preindustrial times, cities consumed foodstuffs produced in rural areas but produced little that rural areas needed in return. As a result, some historians describe preindustrial cities as “economically parasitic.” Following the Industrial Revolution, cities became urgent centers of production and were able to offer a wide variety of manufactured goods to rural areas, becoming vital centers of production as well as consumption. Europe experienced the development of the major cities of its realm during this period. In England, for example, in 1800 only 9 percent of the population lived in urban areas. By 1900, some 62 percent were urban dwellers.

While industrialization alone cannot account for the rapid growth of the European population during the nineteenth century (this growth was underway before industrialization), it is believed to have been responsible for changing patterns of population density on the continent. Between 1750 and 1914, most industrialized nations (England, Belgium, France, Germany) also acquired the highest population densities. This correlation reflects not only the rapid urbanization of these countries but also the high population densities of their urban areas and the improved standards of living associated with industrializing economies.

Working in new industrial cities influenced people’s lives outside of the factories as well. As workers migrated from the country to the city, their lives and the lives of their families were utterly and permanently transformed. For many skilled workers, the quality of life decreased a great deal in the first 60 years of the Industrial Revolution. Skilled weavers, for example, lived well in pre-industrial society as a kind of middle class. They tended their gardens, worked on textiles in their homes or small shops, and raised farm animals. They were their bosses. However, after the Industrial Revolution, the living conditions for skilled weavers significantly deteriorated. They could no longer live at their own pace or supplement their income with gardening, spinning, or communal harvesting.

In the first sixty years or so of the Industrial Revolution, working-class people had little time or opportunity for recreation. Workers spent all the light of day at work and came home with little energy, space, or light to play sports or games. The new industrial pace and factory system were at odds with the old traditional festivals which dotted the village holiday calendar. Plus, local governments actively sought to ban traditional festivals in the cities. In the new working-class neighborhoods, people did not share the same traditional sense of a village community. Owners fined workers who left their jobs to return to their villages for festivals because they interrupted the efficient flow of work at the factories. After the 1850s, however, recreation improved along with the rise of an emerging the middle class. Music halls sprouted up in big cities. Sports such as rugby, cricket, and football became popular. Cities had become the places with opportunities for sport and entertainment that they are today.

There was a necessary trade-off in the Industrial Revolution for the working-class. Material standards of living were in some ways, improving more material goods were produced, so they were available at lower costs, and factories provided a variety of employment opportunities not previously available. At the same time, working conditions were often horrible, and the pay was terrible, and it was often difficult for unskilled workers to move to higher skill levels and escape the working class. The traditional protections of the medieval and early modern eras, such as guilds and mandated wage-and-price standards, were disappearing.

Gradually, very gradually, middle class, or “middling sort,” did emerge in industrial cities, mostly toward the end of the 19th century. Until then, there had been only two major classes in society: aristocrats born into their lives of wealth and privilege, and low-income commoners born in the working classes. However new urban industries gradually required more of what we call today “white collar” jobs, such as business people, shopkeepers, bank clerks, insurance agents, merchants, accountants, managers, doctors, lawyers, and teachers. One piece of evidence of this emerging middle class was the rise of retail shops in England that increased from 300 in 1875 to 2,600 by 1890. Another mark of distinction of the middle class was their ability to hire servants to cook and clean the house from time to time. Not surprisingly, from 1851 to 1871, the number of domestic servants increased from 900,000 to 1.4 million. This small but rising middle class prided themselves on taking responsibility for themselves and their families. They viewed professional success as a result of a person’s energy, perseverance, and hard work.

In this new middle class, families became a sanctuary from stressful industrial life. The home remained separate from work and took on the role of emotional support, where women of the house created a moral and spiritual safe harbor away from the rough-and-tumble industrial world outside. Most middle-class adult women were discouraged from working outside the home. They could afford to send their children to school. As children became more of an economic burden, and better health care decreased infant mortality, middle-class women gave birth to fewer children.

Ironically, life in the middle class still had its downside. Stuck in a new position in the middle of society, the new middle class were hostile both to the aristocracy and to the lower classes. They were angered by their political exclusion from power in a system that still favored aristocrats they felt they had the wealth and education to deserve a political voice. They also had contempt for the lower classes, particularly the growing mass of urban poor. In their lifestyles and political positions, they tried to separate themselves from this uneducated and politically powerless herd, with whom they had less and less culturally in common (and who often worked for them in their factories).

By the early twentieth century additional countries, usually culturally associated with Europe, began to industrialize, including Russia, Japan, other nations in Eastern and Southern Europe, Australia, and New Zealand. Britain and the other previously industrialized countries became highly urbanized. The last craft industries, such as shoemaking and glassmaking, became industrialized. The most developed countries, such as the United States, mass-produced consumer goods – such as dishwashers, furniture, and even houses – for the growing middle classes. The service sector grew and matured with jobs for teachers, waiters, accountants, lawyers, police, and clerks. Essential inventions included the assembly line, the automobile, and the airplane. Western countries and businesses typically controlled world trade and took direct or indirect control of critical industries in less developed countries, enriching themselves in the process.

The Industrial Revolution, an era that began in England at the end of the 18th century, has yet to end. Since the 1950s the so-called “Asian Tigers” (Hong Kong, Singapore, Taiwan, South Korea) rapidly industrialized by taking advantage of their educated and cheap labor to export inexpensive manufactured goods to the West. Other countries in Asia and the Americas, such as China, India, Brazil, Chile, and Argentina, began to develop key economic sectors for export in the global economy.

The world moved gradually toward global free trade. Western countries in Europe and North America turned increasingly to service and high technology economies as manufacturing moved to the cheap labor markets of developing countries. The important new inventions of this phase were the computer and the Internet. This era is now referred to as the “Post-Industrial age,” since the most developed countries focus on service jobs rather than manufacturing, called the “Information Age.” With only a few exceptions, most impoverished nations have not become wealthy in the fiercely competitive global market. There is an increasing wealth gap between more developed and less developed countries in the world.

11.2 The Economies of Geography

It is easier to understand why people move from rural to urban, from the periphery to core, from Mexico to the United States when one begins to understand the global economy. Economic conditions are connected to how countries gain national income, opportunities, and advantages. One way of gaining wealth is simply by taking someone else’s wealth. This method has been common practice throughout human history: a group of armed individuals attacks another group and takes their possessions or resources. This is regularly practiced through warfare. Unfortunately, this pillage-and-plunder type of activity has been a standard way of gaining wealth throughout human history.

The taking of resources by force or by war is frowned upon today by the global economic community, though it still occurs. The art of piracy, for example, is still practiced on the high seas in various places around the globe, particularly off the coast of Somalia.

The main methods countries use to gain national income are based on sustainable national income models and value-added principles. The traditional three areas of agriculture, extraction/mining, and manufacturing are a result of primary and secondary economic activities. Natural resources, agriculture, and manufacturing have been traditionally targeted as the means to gain national income. Postindustrial activities in the service sector, including tertiary, quaternary, and quinary economic activities, have exploded in the past seventy-five or so years.

Services constitute over 50 percent of income to citizens in low-income nations. The service economy is also crucial to growth, for instance, it accounted for 47 percent of economic growth in sub-Saharan Africa over the period 2000 – 2005; industry contributed 37 percent and agriculture 16 percent in the same period. This means that recent economic growth in Africa relies as much on services as on natural resources or textiles, despite many of those countries benefiting from trade preferences in primary and secondary goods. As a result, employment is also adjusting to the changes, and people are leaving the agricultural sector to find work in the service economy. This job creation is particularly useful as often it employs low-skilled labor in the tourism and retail sectors, thus benefiting the poor and representing an overall net increase in employment.

Places around the world have sometimes been named after the methods used to gain wealth. For example, the Gold Coast of western Africa received its label because of the abundance of gold in the region. The term breadbasket often refers to a region with abundant agricultural surpluses. Another example is the Champagne region of France, which has become synonymous with the beverage made from the grapes grown there. The Banana Republic earned their name because their large fruit plantations were the primary income source for the large corporations that operated them. Places such as Copper Canyon and Silver City are examples of towns, cities, or regions named after the natural resources found there.

The United States had its Manufacturing Belt, referring to the region from Boston to St. Louis, which was the core industrial region that generated wealth through heavy manufacturing for the more significant part of the nineteenth and twentieth centuries.

Countries with few opportunities to gain wealth to support their governments often borrow money to provide services for their people. The national debt is a significant problem for national governments. National income can be consolidated into the hands of a minority of the population at the top of the socioeconomic strata. These social elites can dominate the politics of their countries or regions. The elites may hold most of a country’s wealth, while at the same time, their government might not always have enough revenues to pay for public services. To pay for public services, the government might need to borrow money, which then increases that country’s national debt. The government could have a high national debt even when the country is home to many wealthy citizens or a growing economy. Taxes are a standard method for governments to collect revenue. If economic conditions decline, the amount of taxes collected can also decline, which could leave the government with a shortfall. Again, the government might borrow money to continue operating and to provide the same level of services. Political corruption and the mismanagement of funds can also cause a country’s government to lack revenues to pay for the services it needs to provide its citizens. The National debt, defined as the total amount of money a government owes, is a growing concern across the globe.

Many governments have problems paying their national debt or even the interest on their national debt. Governments whose debt has surpassed their ability to pay have often inflated their currency to increase the amount of money in circulation, a practice that can lead to hyperinflation and eventually the collapse of the government’s currency, which could have serious adverse effects on the country’s economy. In contrast to the national debt, the term budget deficit refers to the annual cycle of accounting of a government’s excess spending over the number of revenues it takes enduring a given fiscal year.

11.3 Globalization and international trade

Before we begin a discussion about why nations trade, it would be helpful to take a moment to consider the character and evolution of trade. It is important to keep in mind, first, that although we frequently talk about trade “between nations,” the vast majority of international transactions today take place between private individuals and private enterprises based in different countries. Governments sometimes sell things to each other, or individuals or corporations in other countries, but these comprise only a small percentage of world trade.

Trade is not a modern invention. International trade today is not qualitatively different from the exchange of goods and services that people have been conducting for thousands of years. Before the widespread adoption of currency, people exchanged goods and some services through bartering—trading a certain quantity of one good or service for another good or service with the same estimated value. With the emergence of money, the exchange of goods and services became more efficient.

Developments in transportation and communication revolutionized economic exchange, not only increasing its volume but also widening its geographical range. As trade expanded in geographic scope, diversity, and quantity, the channels of trade also became more complex. Individuals conducted the earliest transactions in face-to-face encounters. Many domestic transactions, and some international ones, still follow that pattern. However, over time, the producers and the buyers of goods and services became more remote from each other.

A wide variety of market actors, individuals and firms, emerged to play supportive roles in commercial transactions. These “middlemen,” wholesalers, providers of transportation services, providers of market information, and others, facilitate transactions that would be too complex, distant, time-consuming, or broad for individuals to conduct face-to-face efficiently.

International trade today differs from economic exchange conducted centuries ago in its speed, volume, geographic reach, complexity, and diversity. However, it has been going on for centuries, and its fundamental character, the exchange of goods and services for other goods and services or money, remains unchanged.

That brings us to the question of why nations trade. Nations trade a lot, but it is not quite as obvious why they do so. Put differently, why do private individuals and firms take the trouble of conducting business with people who live far away, speak different languages, and operate under different legal and economic systems, when they can trade with fellow citizens without having to overcome any of those obstacles?

It seems evident that if one country is better at producing one good and another country is better at producing a different good (assuming both countries demand both goods) that they should trade. What happens if one country is better at producing both goods? Should the two countries still trade? This question brings into play the theory of comparative advantage and opportunity costs.

The everyday choices that we make are, without exception, made at the expense of pursuing one or several other choices. When you decide what to wear, what to eat for dinner, or what to do on Saturday night, you are making a choice that denies you the opportunity to explore other options.

The same holds for individuals or companies producing goods and services. In economic terms, the amount of the good or service that is sacrificed to produce another good or service is known as opportunity cost. For example, suppose Switzerland can produce either one pound of cheese or two pounds of chocolate in an hour. If it chooses to produce a pound of cheese in a given hour, it forgoes the opportunity to produce two pounds of chocolate. The two pounds of chocolate, therefore, is the opportunity cost of producing the pound of cheese. They sacrificed two pounds of chocolate to make one pound of cheese.

A country is said to have a comparative advantage in whichever good has the lowest opportunity cost. That is, it has a comparative advantage in whichever good it sacrifices the least to produce. In the example above, Switzerland has a comparative advantage in the production of chocolate. By spending one hour producing two pounds of chocolate, it gives up producing one pound of cheese, whereas, if it spends that hour producing cheese, it gives up two pounds of chocolate.

Thus, the good in which comparative advantage is held is the good that the country produces most efficiently (for Switzerland, it is chocolate). Therefore, if given a choice between producing two goods (or services), a country will make the most efficient use of its resources by producing the good with the lowest opportunity cost, the good for which it holds the comparative advantage. The country can trade with other countries to get the goods it did not produce (Switzerland can buy cheese from someone else).

The concepts of opportunity cost and comparative advantage are tricky and best studied by example: consider a world in which only two countries exist (Italy and China) and only two goods exist (shirts and bicycles). The Chinese are very efficient in producing both goods. They can produce a shirt in one hour and a bicycle in two hours. The Italians, on the other hand, are not very productive at manufacturing either good. It takes three hours to produce one shirt and five hours to produce one bicycle.

The Chinese have a comparative advantage in shirt manufacturing, as they have the lowest opportunity cost (1/2 bicycle) in that good. Likewise, the Italians have a comparative advantage in bicycle manufacturing as they have the lowest opportunity cost (5/3 shirts) in that good. It follows, then, that the Chinese should specialize in the production of shirts and the Italians should specialize in the production of bicycles, as these are the goods that both are most efficient at producing. The two countries should then trade their surplus products for goods that they cannot produce as efficiently.

A comparative advantage not only affects the production decisions of trading nations, but it also affects the prices of the goods involved. After the trade, the world market price (the price an international consumer must pay to purchase a good) of both goods will fall between the opportunity costs of both countries. For example, the world price of a bicycle will be between 5/3 shirt and two shirts, thereby decreasing the price the Italians pay for a shirt while allowing the Italians to profit. The Chinese will pay less for a bicycle and the Italians less for a shirt than they would pay if the two countries were manufacturing both goods for themselves.

In reality, of course, trade specialization does not work precisely the way the theory of comparative advantage might suggest, for several reasons:

Generally, countries with a relative abundance of low-skilled labor will tend to specialize in the production and export of items for which low-skilled labor is the predominant cost component. Countries with a relative abundance of capital will tend to specialize in the production and export of items for which capital is the predominant component of cost.

Many American citizens do not fully support specialization and trade. They contend that imports inevitably replace domestically produced goods and services, thereby threatening the jobs of those involved in their production.

Imports can indeed undermine the employment of domestic workers. We will return to this subject a little later. From what you have just read, you can see that imports supply products that are either 1) unavailable in the domestic economy or 2) that domestic enterprises and workers would be better off not making so that they can focus on the specialization of another good or service.

Finally, international trade brings several other benefits to the average consumer. Competition from imports can enhance the efficiency and quality of domestically produced goods and services. Also, competition from imports has historically tended to restrain increases in domestic prices.

Global Interdependence

The tremendous growth of international trade over the past several decades has been both a primary cause and effect of globalization. The volume of world trade increased twenty-seven-fold from $296 billion in 1950 to $8 trillion in 2005. Although international trade experienced a contraction of 12.2 percent in 2009, the steepest decline since World War II, trade is again on the upswing.

As a result of international trade, consumers around the world enjoy a broader selection of products than they would if they only had access to domestically made products. Also, in response to the ever-growing flow of goods, services, and capital, a whole host of U.S. government agencies and international institutions have been established to help manage these rapidly developing trends.

Although increased international trade has spurred tremendous economic growth across the globe, raising incomes, creating jobs, reducing prices, and increasing workers’ earning power, trade can also bring about economic, political, and social disruption.

Since the global economy is so interconnected, when large economies suffer recessions, the effects are felt around the world. One of the hallmark characteristics of the global economy is the concept of interdependence. When trade decreases, jobs, and businesses are lost. In the same way that globalization can be a boon for international trade; it can also have devastating effects. Activities such as the choice of clothes you buy have a direct impact on the lives of people working in the nations that produce

There are several elements that are responsible for the expansion of the global economy during the past several decades: new information technologies, reduction of transportation costs, the formation of economic blocs such as the North American Free Trade Association (NAFTA), and the reforms implemented by states and financial organizations in the 1980s aimed at liberalizing the world economy.

Trade liberalization, or deregulation, has become a ‘hot button’ issue in world affairs. Many countries have seen great prosperity thanks to the disintegration of trade regulations that had otherwise been considered a harbinger of free trade in the recent past. The controversy surrounding the issue, however, stems from enormous inequality and social injustices that sometimes comes with reducing trade regulations in the name of a bustling global economy.

Given the dislocations and controversies, some people question the importance of efforts to liberalize trade and wonder whether the economic benefits are outweighed by other unquantifiable negative factors such as labor exploitation.

With globalization, competition occurs between nations having different standards for worker pay, health insurance, and labor regulations. Corporations benefit from lower labor costs found in developing regions, thanks to free-trade agreements and a new international division of labor. A worker in a high-wage country is thus increasingly struggling in the face of competition from workers in low-wage countries. Entire sectors of employment in developed countries are now subject to this growing international competition, and unemployment has crippled many localities.

The outcome has been an international division of labor in all sectors of the economy. In particular, manufacturing is increasingly being contracted out to lower- cost locations, which are often found in developing countries with no minimum wage and few environmental regulations.

An excellent example of international division of labor can be found in the clothes-making industry. What was once a staple industry in most developed Western economies has now been relocated to developing countries in Central America, Eastern Europe, North Africa, Asia, and elsewhere.

Chapter 12 Urban Geography for print only


12.1 Defining Cities and Urban Centers

Cities and metropolis

You are probably a city person whether you like it or not. Many people say they do not like the city, with its noise, pollution, crowds, and crime, but living outside the city has its challenges as well. Living outside a city is inconvenient because rural areas lack access to the numerous amenities found in cities. The clustering of activities within a small area is called agglomeration, and it reduces the friction of distance for thousands of daily activities. Cities are convenient places for people to live, work, and play. Convenience has economic consequences, as well. Reduced costs associated with transportation, and the ability to share costs for infrastructure creates what is known as economies of agglomeration, which is the fundamental reason for cities. The convenience and economic benefits of city life have led nearly 8 in 10 Americans to live in urban areas. In California, America’s most urban state, almost 95% of its people live in a city. This chapter explores the evolution of cities, why cities are where they are, and how the geography of cities affects the way urbanites live.

Though it seems simple enough, distinguishing cities from rural areas is not always that easy. Countries around the world have generated a plethora of definitions based on a variety of urban characteristics. Part of the reason stems from the fact that defining what constitutes urban is somewhat arbitrary. Cities are also hard to define because they look and function quite differently in different parts of the world. Complicating matters are the great variety of terms we use to label a group of people living together. Hamlets are tiny, rural communities. Villages are slightly larger. Towns are larger than villages. Cities are larger than towns. Then there are words like metropolis and even megalopolis to denote huge cities. Some states in the United States have legal definitions for these terms, but most do not. The United States Census Bureau creates the only consistent definition of “city,” and it uses the terms “rural” and “urban” to distinguish cities from non-city regions. This definition has been updated several times since the 1800s, most radically in recent years as the power of GIS has allowed the geographers are working for the US Census Bureau to consider multiple factors simultaneously. It can get complex.

For decades, the US Census Bureau recognized an area as “urban” if it had incorporated itself as a city or a town. Incorporation indicates that a group of residents successfully filed a town charter with their local state government, giving them the right to govern themselves within a specific space within the state. Until recently, the US Census Bureau classified almost any incorporated area with at least 2,500 people as “urban.”

There were problems though with that simple definition. Some areas which had quite large populations but were unincorporated, failed to meet the old definition or urban. For example, Honolulu, Hawaii, and Arlington, Virginia are not incorporated, therefore were technically labeled “census-designated places,” rather than cities. Conversely, some incorporated areas may have very few people. This can happen when a city loses population, or when the boundaries of a city extend far beyond the populated core of the city. You may have witnessed this as you are driving on a highway, and you see a sign indicating “City Limits,” but houses, shops, factories and other indicators of urban life are absent yet for many miles. Jacksonville, Florida, is the classic example of this problem. Jacksonville annexed so much territory that its city limits extend far into the adjacent countryside making it the largest city in land area in the United States (874.3 square miles!).

Therefore, the Census Bureau created a complex set of criteria capable of evaluating a variety of conditions that define any location as urban or rural. Among the criteria now used by the Census is a minimum population density of 1,000 people per square mile, regardless of whether the location is incorporated or not. Additionally, a territory that includes non-residential but still urban land uses is included. Therefore, areas with factories, businesses, or a large airport, that contain few residences still counted as part of a city. The Census uses a measure of surface imperviousness to help make such a decision. This means that even a parking lot may be a factor in classifying a place as urban. Finally, the census classifies locations that are reasonably close to an urban region if it has a population density of at least500 persons per square mile. That way, small breaks in the continuity of built-up areas do not result in the creation of multiple urban areas, but instead form a single, contiguous urban region. Therefore, people in the suburbs within five miles of the border of a larger city, are counted by the Census as residents of the urban region, associated with a central city.

City push and pull factors

Cities began to form many thousands of years ago, but there is little agreement regarding why cities form. The chances are that many different factors are responsible for the rise of cities, with some cities owing their existence to multiple factors and cities arose as a result of more specific conditions.

Two underlying causal forces contribute to the rise of cities. Site location factors are those elements that favor the growth of a city that is found at that location. Site factors include things like the availability of water, food, good soils, a quality harbor, and characteristics that make a location easy to defend from attack. Situation factors are external elements that favor the growth of a city, such as distance to other cities, or a central location. For example, the exceptional distance invading armies have had to travel to reach Moscow, Russia has helped the city survive many wars. Most large cities have good site and situation factors.

Indeed, the earliest incarnation of cities offered residents a measure of protection against violence from outside groups for thousands of years. Living in a rural area, farming or ranching, made any family living in such isolation vulnerable to attack. Small villages could offer limited protection, but larger cities, especially those with moats, high walls, professional soldiers, and advanced weaponry, were safer.

The safest places were cities with quality defensible site locations. Many of Europe’s oldest cities were founded on defensible sites. The European feudal system was built upon an arrangement whereby the local lord/duke/king supplied protection to local rural peasants in exchange for food and taxes. For example, Paris and Montreal were founded on defensible island sites. Athens was built upon a defensible hillside, called an acropolis. The Athenian Acropolis is so famous that it is called merely The Acropolis. On the other hand, Moscow, Russia, takes advantage of its remote situation. Both Napoleon and Hitler found out the hard way the challenges associated with attacking Moscow.

In the United States, the Atlantic and Pacific Oceans have primarily functioned as America’s defensive barriers, and therefore few cities are located on defensive sites. Washington, D.C. has no natural defense-related site or situation advantages. On the only occasion the US was invaded, the city was overrun by the British in the War of 1812. The White House and the Capitol were burned to the ground. The poor defensibility of the American capital led to numerous calls for its relocation to a more defensible site during the 1800s. This is partly the reason, so many state-capitol buildings in the Midwest closely resemble the US Capitol building in Washington D.C.; many states were trying to lure the seat of the Federal government to their state capital.

People who possess a specific skill set to become a site factor that can significantly affect the location and growth of a city. One specialized skill set was confined to the priestly class, and proximity to religious leaders is another probable reason for the formation of cities. Priests and shamans would have likely gathered the faithful near to them, so that, as the armies of the lordly class, they could offer protection and guidance in return for food, shelter, and compensation (like tithes). The priestly class was also the primary vessels of knowledge – and the tools of knowledge like writing and science (astronomy, planting calendars, medicine, e.g.), so a cadre of assistants in those affairs would have been necessary. Mecca and Jerusalem are probably the best examples of holy cities, but others dot the landscape of the world. Rome existed before the Catholic faith, but it assuredly grew and prospered as a result of becoming the headquarters of Christianity for hundreds of years.

Cities may have evolved as small trading posts where local farmers and wandering nomads exchanged agricultural and craft goods. The surplus wealth generated through trade required protection and fortifications, so cities with walls may have been built to protect marketplaces and vendors. Some trace the birth of London to an ancestral trading spot called Kingston upon the Thames, a market town founded by the Saxons southwest of London’s present core. The place names of many ancient towns in England reveal their original function – Market Drayton, Market Harborough, Market Deeping, Market Weighton, Norton Chipping, Chipping Ongar and Chipping Sodbury. “Chipping” is a derivation of a Saxon word meaning “to buy.”

Throughout history, cities, big and small, have served market functions for those who live in adjacent hinterlands. Some market cities grow much more substantial than others because they are more centrally located. Central location relative to other competing marketplaces is another example of an ideal situation factor. Large cities have excellent site and situation characteristics. Every major US city, including New York, Chicago, Los Angeles, Atlanta, and Houston is located ideally for commerce and industry.

Photo by Emiliano Bar on Unsplash

Some cities grow large because of specific site location advantages that favor trade or industry. All cities compete against one another to attract industry, but only those with quality site factors, like excellent port facilities and varied transportation options grow large. Cities ideally located between significant markets for exports and imports have excellent situation factor advantages versus other competing cities and will grow most.

Most large cities in the United States emerged where two or more modes of transportation intersect, forming what geographers call a break of bulk point. Breaking bulk happens whenever cargo is unloaded from a ship, truck, barge, or train. Until the 1970s, unloading (and reloading) freight required a vast number of laborers, and therefore any city that had a busy dock or port or station attracted workers. Los Angeles, Chicago, New Orleans, and Houston all grew very large because each was well served by multiple transportation modes.

12.2 Understanding Distribution and City Size

Under very unusual circumstances, one might find that among a group of cities, no single city has unique site location advantages over others. This might happen out on a vast plain, like in Kansas, where there are no navigable rivers, waterfalls or ports. In instances like this, situation advantages come to the fore, and a regular, geometric pattern of cities may emerge. This process was more pronounced when transportation was primitive, and the friction of distance was considerable, but it can still be witnessed by picking up a map of almost any flat region of the earth. Geographer Walter Christaller noticed the pattern and developed the Central Place Theory to explain the pattern and the logic driving it forward.

Central Place Theory. This diagram represents an idealized urban hierarchy in which people travel to the closest local market for lower-order goods, but must go to a larger town or city for higher orders goods.

According to Christaller, if a group of people (like farmers) diffuse evenly across a plain (as they were when Kansas opened for homesteaders), a predictable hierarchy of villages, towns, and cities will emerge. The driving force behind this pattern is the basic need everyone has to go shopping for goods and services. Naturally, people prefer to travel less to acquire what they need. The maximum distance people will travel for a good or service is called the range of that good or service. Goods like a hammer have a short range because people will not travel far to buy a hammer. A tractor, because it is an expensive item, has a much greater range. The cost of getting to a tractor dealership is small about the cost of the tractor itself, so farmers will travel long distances to buy the one they want. Hospital services have even greater ranges. People might travel to the moon if a cure for a deadly disease was available there.

Each merchant and service provider also requires a minimum number of regular customers in order to stay in business. Christaller called this number the threshold population. A major-league sports franchise has a threshold population of probably around a million people, most of whom must live in that team’s range. There are only 30 Major League Baseball teams in the United States, and the team with the smallest market (Milwaukee Brewers) has a threshold population of 2 million people. An ordinary Wal-Mart store probably has a threshold of about 20,000 people, so they are far more numerous. Starbuck’s Coffee shops probably have a threshold of about 5,000 people or less, because there are so many locations.

When customers and merchants living and working on featureless plain interact over time, some villages will attract more merchants (and customers) and grow into towns or even cities. Some villages will not be able to attract or retain merchants, and they will not grow. Competition between towns on this plain prevents nearby locations from growing simultaneously. As a result, centrally located villages tend to grow into towns at the expense of their neighbors. A network of centrally located towns, will emerge, and among these towns, only a few will grow into cities. One very centrally located city may evolve into a much larger city.

The largest cities will have business and functions that require significant thresholds (like major league sports teams or highly specialized boutiques). People from villages and small towns can access only the most essential goods and services (like gas stations or convenience stores) and are forced to travel to larger cities to buy higher order goods and services. Those goods and services not available to the nearest large city (regional service center) require customers to travel further. Some goods and services are only available at the top of the urban hierarchy; the mega-cities. In the United States, a handful of cities (New York, Los Angeles, Chicago, and Dallas) may offer exceptionally high order goods, unavailable in other large cities like Cleveland, Seattle or Atlanta.

Understanding Internal City Structure and Urban Development

Most urban centers begin in the downtown region called the central business district (CBD). The CBD tends to be the node or of transportation networks along with commercial property, banking, journalism, and judicial departments like City Hall, courts, and libraries. Because of high competition and limited space, property values for commercial and private ownership tend to be at a premium. CBDs also tend to use land above and below ground in the form of subways, underground malls, and high- rises. Sports facilities and convention centers also tend to be dominating forces in CBDs.

Urban planning is a sub-field of geography and until recently was part of geography departments in academia. An urban planner is someone trained in multiple theories of urban development along with developing ways to minimize traffic, decrease environmental pollution, and build sustainable cities. Urban planners, sociologists, along with geographers, have come up with three models to demonstrate and explain how cities grow.

The first model is called the concentric zone model, which states that cities can develop in five concentric rings. The inner zone of the cities tends to be the CBD, followed by a second ring that tends to the zone of transition between the first and third rings. In this transition zone, the land tends to be used by industry or low-quality housing. The third ring is called the zone of independent workers and tends to be occupied by working-class households. The fourth ring is called the zone of better residences and is dominated by middle-class families. Finally, ring five is called the commuter’s zone, where most people living there have to commute to work every day.

The second model for city development and growth is called the sector model. This model states that cities tend to grow in sectors rather than concentric rings. The idea behind this model is that “like groups” tend to grow in clusters and expand as a cluster. The center of this model is still the CBD. The next sector is called the transportation and industry sector. The third sector is called the low-class residential sector, where lower-income households tend to group. The fourth sector is called the middle-class sector, and the fifth is the high-class sector.

The third and final urban design is called the multiple nuclei model. (See figure 7.16) In this model, the city is more complex and has more than one CBD. A node could exist for the downtown region, another where a university is situated, and maybe another where an international airport may be. Some clustering does exist in this model because some sectors tend to stay away from other sectors. For example, the industry does not tend to develop next to high-income housing.

The multiple nuclei model also features zones common to the other models. Industrial districts in these new cities, unfettered by the need to access rail or water corridors, rely instead on truck freight to receive supplies and to ship products, allowing them to occur anywhere zoning laws permitted. In western cities, zoning laws are often far less rigid than in the East, so the pattern of industrialization in these cities is sometimes random. Residential neighborhoods of varying status also emerged in a nearly random fashion as well, creating “pockets” of housing for both the rich and poor, alongside large zones of lower-middle-class housing. The reasons for neighborhoods to develop where they do are similar as they are in the sector model. Amenities attract wealthier people, transport advantages attract industry and commerce, and disamenity zones are all that poor folks can afford. There is a sort of randomness to multiple nuclei cities, making the landscape less legible for those not familiar with the city, unlike concentric ring cities that are easy to read by outsiders who have been to other similar cities.

Another model is referred to as “Keno Capitalism.” In this model, based in Los Angeles, different districts are laid out in a mostly random grid, similar to a board used in the gambling game keno. The premise of this model is that the internet and modern transportation systems have made location and distance mostly irrelevant to the location of different sorts of activities within a city.

Geographers Ernest Griffin and Larry Ford recognized that the popular urban models did not fit well in many cities in the developing world. In response, they created one of the more compelling descriptions of cities formerly colonized by Spain – the Latin American Model. The Spanish designed Latin American cities according to rules contained in the Spanish Empire’s Law of the Indies. According to these rules, each significant city was to have at its center a large plaza or town typical for ceremonial purposes. A grand boulevard along which housing for the city’s elite was built stretched away from the central plaza and served as both a parade route and opulent promenade. For several blocks outward from this elite spine was built the housing for the wealthy and powerful.

Latin America Model

The rest of the city was initially left for the poor because there was almost no middle class. The poorly built houses close the central plaza where jobs and conveniences existed. Over time, the houses built by the poor, perhaps little more than shacks, were improved and enlarged. Ford and Griffin called this process in situ accretion. As the city’s population grew, young families and in-migrants built still more shacks, adding rings of housing that is always being upgraded. At the edges of the city are always the newest residents, often squatting on land they do not own.

Sociologists, geographers, and urban planners know that no city exactly follows one of the urban models of growth. However, the models help us understand the broader reason why people live where they do. Higher income households tend to live away from lower income households. Renters and house owners also tend to segregate from each other. Renters tend to live closer to the CBD, whereas homeowners tend to live in the outer regions of the city. It should be noted that the three models were developed shortly after World War II and based on U.S. cities; many critics now state that they do not truly represent modern cities.


A megacity is pegged as any city with more than 10 million residents. Another term often used to describe this is conurbation, a somewhat more comprehensive label that incorporates agglomeration areas such as the Rhine-Ruhr region in Germany’s west which has 11.9 million inhabitants.

Of the 30 biggest megacities worldwide, 20 of them are in Asia and South America alone, including Baghdad, Bangkok, Buenos Aires, Delhi, Dhaka, Istanbul, Jakarta, Karachi, Kolkata, Manila, Mexico City, Mumbai, Osaka-Kobe-Kyoto, Rip de Janeiro, Sao Paulo, Seoul, Shanghai, Teheran, and Tokyo-Yokohama. European megacities include London and Paris, and the UN estimates that the number of megacities worldwide will only increase.

The explosive growth of these and other cities is a rather new phenomenon, a result of industrialization. The megacities of the world differ not only according to whether they lie in the southern or northern hemisphere, but also by country, climatic, political, economic, and social conditions. Megacities can be productive, poor, organized, or chaotic. Paris and London are megacities, but it is difficult to compare them demographically or economically with Jakarta or Lagos. Vibrant megacities tend to stretch out further than their poorer counterparts: Los Angeles’ settlement area is four times as big as Mumbai’s despite its population being smaller. Wealthy city inhabitants have a much higher rate of land consumption for apartments, transport, business, and industry. The situation is similar in terms of water and energy consumption, which is much higher in affluent cities. Cairo and Dhaka are without doubt ‘monster cities’ in terms of their population size, spatial, and urban planning. However, they are also “resourceful cities,” home to millions of people with few resources.

The high population levels in megacities and mega-urban spaces are leading to a host of problems such as guaranteeing all residents a supply of essential foods, drinking water and electricity. Related to this are concerns about sanitation and disposal of sewage and waste. There is not enough living space for incoming residents, leading to an increase in informal settlements and slums. Many urban residents get around via bus, truck or motorized bicycles, leading to chaos on the streets and CO2 emissions leaking into the air.

The faster a city develops, the more critical these issues become. Due to their rapid growth, megacities in developing countries and the southern hemisphere have to battle in order to provide for their inhabitants. Between 1950 and 2000, cities in the north have grown an average of 2.4 times. In the south, they have grown more than 7-fold over the same period. Lack of financial resources and sparse coordination between stakeholders at different levels intensify the problems. Megacities usually do not represent one political-administrative unit, instead of dividing the city into parts such as with Mexico City, which is made up of one primary core district (Distrito Federal) and more than 20 outlying municipalities, where differing planning, construction, tax, and environmental laws are carried out than in the core district.

Two key causes behind city growth are high rates of immigration as well as growing birth numbers. People move to the city with the hope of a more prosperous life and leave the country in search of brighter prospects. Without careful planning and infrastructure in place, this road can often lead to another poverty trap. As cities grow, so too do the unplanned and underserved areas, the so-called slums. In some regions of the world, more than 50 percent of urban populations live in slums. In parts of Africa south of the Sahara, that number jumps to around 70 percent. In 2007, a reported one billion people lived in slums, and by 2020, that figure could grow to 1.4 billion, according to the UN.

The United Nations defines slums as overcrowded, inadequate, informal forms of housing that lack reasonable access to clean drinking water and sanitary facilities and deprive residents of power of the land. Above all, slums are an architectural and spatial expression of lack of housing and growing urban poverty. The well-known symbols of this are makeshift huts, such as the favelas in Brazil, but also desolate and overcrowded apartment buildings in major Chinese cities where the growing army of migrant workers and workers find makeshift accommodation.

The reasons so many of these cities are poor include underemployment and insufficient pay as well as low productivity within the informal sector. Around half the people in megacities that lie in the southern hemisphere are employed in the informal sector, many of whom are coerced into accepting any employment. They sell various products – cigarettes, drinks, food, bits, and pieces – simple services like shoe cleaning and letter writing as well as smuggling goods or ending up in prostitution. Exploitation is, at times, rife in slum settings due to insecure residences, lack of legal protection, poor sanitation, and unstable acquisition conditions.

Parallel to the growth of slums, gated communities – or exclusive neighborhoods – are also on the rise. These are fenced and well-monitored communities in which affluent members live, further driving the trend towards separation among urban populations.

However, it is not just living spaces splitting the cities – globally; there is a significant push towards big new building projects like über-modern banks and business districts which stand in stark contrast to informal areas for the poor. These central business districts (CBD) are often siloed off from the central part of the city and migrate, along with the gated communities, towards the outskirts of town as is the case in Pudong, Shanghai, and Beijing.

For the most part, urban planning is based on the needs of the consumer and culture-oriented upper classes and economic growth sectors, with the result being that the gap between rich and poor continues to grow. Such fragmented cities are a fragile entity in which conflicts are inevitable.

Because most people on the planet are city-dwellers, questions are starting to be asked about how to develop and design urbanization and urban migration in a sustainable way. Urban residents the world over require good air to breathe, clean drinking water, access to proper healthcare, sanitary facilities, and reliable energy supply.

The current situation in cities in developing countries can be precarious: the air is thick enough to touch; sewage treatment plants, if any, are overloaded and industrial factories secrete virtually unregulated highly toxic waste and wastewater. Also, climate change will likely hit more impoverished cities harder. However, cities in the developed countries have to deal with environmental challenges in the areas of transport, energy and waste and wastewater.

On an international level, there are countless efforts currently being undertaken to support sustainable urban development. Several large UN projects, such as the UN-HABITAT Program and the Sustainable Urban Development Network are endeavoring to improve and strengthen governmental and planning abilities. One of the goals of the UMP is also to implement the Millennium Development Goals at the city level.

Many urban problems can be explained not only at the city level, but must be regarded as results of political disorder and economic instability on a global and national level – and that this is where the solutions lie!

12.3 Challenges to Urban Growth

One of the major problems that cities face is deteriorating areas, high crime, homelessness, and poverty. As noted in the urban models, many lower-income people live near the city, but lack the job skills to compete for employment within the city. This often results in a variety of social and economic problems. Census data shows that 80 percent of children living in inner cities only have one parent, and because child care services are limited in the city, single parents struggle to meet the demands of childcare and employment. Problems associated with lower income areas are often violent crime (assault, murder, rape), prostitution, drug distribution, and abuse, homelessness, and food deserts.

Slums and Shanty Towns

Some of these inner-city areas are slums, which is a densely populated urban informal settlement consisting of poor, inadequate living standards. Most slums lack proper sanitation services, access to clean drinking water, law enforcement, or other necessities of living in an urban area.

A shanty town, also known as a squatter, is a slum settlement that usually consists of building material made from plywood sheets of plastic, cardboard boxes, and other cheap material. They are usually found on the periphery of cities or near rivers, lagoons, or city trash dumps.

When residents in a neighborhood lack the money, political organizational skills, or the motivation to protect themselves from disamenities, defined as drawbacks or disadvantages, especially about location, significant neighborhood degradation is possible. Poor people of all ethnicities can rarely afford to live in neighborhoods that have the outstanding schools, parks, air quality, etc., and so they are often able to afford to live only in the most dangerous, toxic, degraded neighborhoods. Racism is undoubtedly a common variable in the poverty equation, but it is rarely the only one.


As a way for city officials to deal with inner-city problems, there has been a push recently to renovate cities, a process called gentrification. Middle-class families are drawn to city life because housing is cheaper, yet can be fixed up and improved, whereas suburb housing prices continue to rise. Some cities also offer tax breaks and cheap loans to families who move into the city to help pay for a renovation. Also, city houses tend to have more cultural style and design compared to quickly made suburb homes. Transportation tends to be cheaper and more convenient, so that commuters do not spend hours a day traveling to work. Couples without children are drawn to city living because of the social aspects of theaters, clubs, restaurants, bars, and recreational facilities.

The logic behind gentrification is that it not only reduces crime and homelessness; it also brings tax revenue to cities to improve the city’s infrastructure. However, there has also been a backlash against gentrification because some view it as a tax break for the middle and upper class rather than spending much-needed money on social programs for low-income families. It could also be argued that improving lower class households would also increase tax revenue because funding could go toward job skill training, child care services, and reducing drug use and crime.


Homelessness is another primary concern for citizens of large cities. More than one half- million people are believed to live on the streets or in shelters. In 2013, about one- third of the entire homeless population were living as a member of a family unit. One-fourth of homeless people were children. In Los Angeles County at the same time, there were somewhere around 40,000 homeless people living either in shelters and on the street. Another 20,000 persons were counted as near homeless or precariously housed, typically living with friends or acquaintances in short-term arrangements.

There are multiple reasons why people become homeless. The Los Angeles Homeless Authority estimates that about one-third of the homeless have substance abuse problems, and another third are mentally ill. About a quarter have a physical disability. A disturbing number are veterans of the armed forces or victims of domestic abuse. Economic conditions locally and nationally also have a significant impact on the overall number of homeless people in a particular year, not only because during recessions people lose their jobs and homes, but because the stresses of poverty can worsen mental illness.

The government plays a significant role in the pattern and intensity of homelessness. Ronald Reagan is the politician most associated with the homeless crisis both nationally and in California. When Reagan became governor of California, the late 1960s, deinstitutionalization of people with a mental health condition was already a state policy. Under his administration, state-run facilities for the care of mentally ill persons were closed and replaced by for-profit board and care homes. The idea was that people should not be locked up by the state solely for being mentally ill and that government-run facilities could not match the quality and cost-efficiency of privately run boarding homes. Many private facilities, though were severely run, profit-driven, located in poor neighborhoods and had little professional staff. Patients could, and did, leave these facilities in large numbers, frequently becoming homeless or incarcerated. Other states followed California’s example. By the late 1970s, the federal government passed some legislation to address the growing crisis, but sweeping changes in governmental policy at the federal level during the Regan presidency shelved efforts started by the Carter administration. Drastic cuts to social programs during the 1980s ensured an explosion of mental illness related homelessness. Most funding has never been restored, though the Obama administration has aggressively pursued policies aimed at housing homeless veterans.

Though homeless people come from many types of neighborhoods, facilities for serving homeless populations are not well distributed throughout the urban regions. Many cities have a region known as Skid Row, a neighborhood unofficially reserved for the destitute. The term originated as a reference to Seattle’s lumber yard areas where workers used skids (wooden planks) to help them move logs to mills. Today, many of the shelters and services for the homeless are found in and around skid row.

12.4 Urban and Suburban Sprawl

Not all of a city’s residents live within the urban cores. Over half of all people live in the suburbs rather than in the city or rural areas. There was a suburban sprawl model developed to explain U.S. development called the peripheral model. This model states that urban areas consist of a CBD followed by large suburban are of business and residential developments. The outer regions of the suburbs become transition zones of rural areas.

The attraction to suburbs is low crime rates, lack of social and economic problems, detached single-family housing, access to parks, and usually better schooling. These are nationwide generalizations and not necessarily true everywhere. Suburbs also tend to create economic and social segregation, where tax revenues and social resources provide better funding opportunities than in inner cities.

Of course, there is also a cost to suburban sprawling. Developers are always looking for cheaper land to build, which usually means developing rural areas and farmland rather than expanding next to existing suburbs. Air pollution and traffic congestion also become a problem as working households are required to travel farther to and from work. Suburbs tend to be less commuter friendly to those who walk or bike because the model of development is based around vehicle transportation.

Water is another challenge to urban growth. It is an elemental part of the fabric of urban lives, providing sustenance and sanitation, commerce, and connectivity. Our fundamental needs for water have always determined the location, size, and form of our cities, just as water shapes the character and outlook of their citizens. Urban health is inextricably linked with water. From the first cities, planners have appreciated the potential linkages of water with health and the need for consistent water supplies. Indeed, the modern field of public health owes a substantial debt to the sanitary engineers who strove to provide potable water and safe disposal of human wastes in burgeoning cities of the Industrial Revolution.

Scientists and decision-makers have recently begun to appreciate that, as in the case of other urban systems, the linkages between water management, health and sustainability are involved in ways that undermine the effectiveness of traditional approaches. Unprecedented urban populations and densities, intra-urban inequities, and inter-urban mobility pose serious new problems, and climate change adds a novel and uncharted dimension. This has, in some cases, led to worsening urban health, or increased risks—for instance, some water-associated diseases like dengue are on the rise globally while others, like cholera, nominally controlled in the developed countries, continue to pose serious threats elsewhere; many regions face increased food and water scarcity, and many urban slums present conditions that challenge effective water management.

12.5 Cities as a Place

In one way, cities are vast, complex machines that produce goods and services, but that way of conceiving the city overlooks genuine emotional qualities that define almost any location. Most people would argue that cities have personalities; qualities that define them as a place. People who live in particular cities often develop a sort of tribal attitude toward their city. This attitude is reflected most visibly in the genuine, emotional attachment citizens have to their sports teams. It is not uncommon for citizens of a city to take great offense at derogatory remarks directed toward “their city,” especially if those remarks come from an outsider.

How we know what we know about cities is primarily bound up in the symbolism of cities provided us through countless media. Often people have enormous storehouses of knowledge about specific places (New York, Paris, Hollywood), even though they have never even visited. We also have powerful ideas about generic places, “small towns,” “the suburbs,” “the ghetto,” even though we may not have visited these places either. This knowledge is imperfect and may very well be dangerously inaccurate to both those people who live in these places and us. It is essential that we recognize how our knowledge of places has been constructed, and we must seek to understand what purposes these constructions serve.

Geographer Donald Meinig proposed that Americans have particularly strong ideas and emotions about three unique, but generic landscapes: The New England Village, Small Town America and the California Suburb (Meinig’s Three Landscapes). Scholars who specialize in the theory of knowledge would suggest these are landscapes are “always already” known; because the symbolism associated with them is deeply ingrained in our collective thoughts, despite that fact that we are hard-pressed to identify how we came to understand the symbolism associated with these places.

Meinig’s first symbolic landscape is the sleepy New England Village, with its steepled white church and cluster of tidy homes surrounded by hardwood forests is powerfully evocative of a lifestyle centered around family, hard work, prosperity, Christianity, and community. He called its rival from the American Midwest Main Street USA. This landscape is found in countless small towns, and symbolizes order, thrift, industry, capitalism, and practicality. It is less cohesive and less religious than the New England Village, and more focused on business and government. Finally, Meinig points to the California Suburb as the last of the significant urban landscapes deeply embedded in the national consciousness. Suburban California symbolizes the good-life: backyard cookouts with the family and neighbors, a prosperous, healthy lifestyle, centered on family leisure.

So powerful are these images that they often appear as settings for novels, movies, television shows as well as political or product advertising campaigns. If you were a manufacturer of high-quality home furnishings, you might want to use the landscape of New England to help sell a well-built dining room table. Insurance companies, like to evoke images of Main Street USA when they want to sign you up for a policy; “like a good neighbor,” they might tell you, hoping you will trust the company, even though its headquarters is not in a small farming town. E.T., the famous movie about a boy who befriends a lost space alien is set in a “typical California suburb.” Like the other symbolic landscapes, movie audiences do not need to have the setting explained to them; they always already know what that place means. Indeed, there are other symbolic landscapes.

Cultural Reflections in Urban Landscapes

The built environment is a product of socio-economic, cultural, and political forces. Every urban system has its own ‘genetic code,’ expressed in architectural and spatial forms that reflect a community’s values and identity. Each community chooses specific physical characteristics, producing the unique character of its city. This ‘communal eye’ exemplifies the city’s architectural legacy and gives a sense of place.

For example, in old Sana’a, the capital of Yemen, unique buildings decorated with geometric patterns create a distinctive visual character unique to the city (Figure 7.23) Another example is Egypt’s Nubian village (Figure 7.24) where the building materials and colors are unique and reflect the vernacular architecture of the region.

However, current architectural practices, in almost every city in the world, do not respect the past identities and traditions of our cities. Most projects bear little or no relationship to the surrounding urban context the city’s genetic code. Architects only follow international architectural movements such as “Modern architecture,” “Postmodernism,” “High-Technology,” and “Deconstructionism.” The result is a fragmented and discontinuous dialogue among buildings, destroying a city’s communal memory.

Street art and graffiti have been filling this gap, explaining the conflict between the traditional culture and contemporary sociopolitical issues of cities. Street artists are repurposing city walls to highlight heritage, history, and identity and, in some cases, to humanize this struggle. Each city has a unique wall art that has become part of its overall genetic code. Some of the art in Santiago (Figure 7.25), for example, highlights Chilean identity. Another example is how wall art was used during the Egyptian revolution to memorialize the events. In March 2012, young graffiti artists launched the “No Walls” movement when the Egyptian authorities constructed several concrete walls to block important street junctions to control peaceful demonstrations.

Many scholars of urban morphology suggest that the street network of any city is made up of a dual network −the foreground network, consisting of the main streets in the urban system, and background network, made up of alleyways or smaller streets. The foreground network, or the leading street network, usually have a universal form, a ‘deformed wheel’ structure composed of small semi-grid street pattern in the center (hub) linked with at least one ring road (rim) through diagonal streets (spokes). However, the form of the background network differs from a city to another; therefore, it is this network that gives a city its spatial identity.

Many cities such as London, Tokyo, and Cairo have a similar universal street pattern of a ‘deformed wheel’ in foreground network despite having different background networks, possibly as a result of cultural differences or contributing to the creation of those cultural differences. In short, the background network reflects the unique structure of each city, and could be considered its genetic code.

Economic Development and City Infrastructure

The evidence of the definite link between urban areas and economic development is overwhelming. With just 54 percent of the world’s population, cities account for more than 80 percent of global GDP. Figure 7.24 and Figure 7.25 respectively show the contribution of cities in developed and developing countries to national income. In virtually all cases, the contribution of urban areas to national income is more significant than their share of the national population. For instance, Paris accounts for 16 percent of the population of France, but generates 27 percent of GDP. Similarly, Kinshasa and metro Manila account for 13 percent and 12 percent of the population of their respective countries, but generate 85 percent and 47 percent of the income of the democratic republic of Congo and Philippines respectively. The ratio of the share of urban areas’ income to share of the population is more considerable for cities in developing countries vis-à-vis those of developed countries. This is an indication that the transformative force of urbanization is likely to be higher in developing countries, with possible implications for harnessing the positive nature of urbanization.

The higher productivity of urban areas stems from agglomeration economies, which are the benefits firms and businesses derive from locating near to their customers and suppliers in order to reduce transport and communication costs they also include proximity to a vast labor pool, competitors within the same industry and firms in other industries.

These economic gains from agglomeration can be summarized as three essential functions: matching, sharing, and learning. First, cities enable businesses to match their distinctive requirements for labor, premises, and suppliers better than smaller towns because a more extensive choice is available. Better matching means greater flexibility, higher productivity, and stronger growth. Second, cities give firms access to a bigger and improved range of shared services, infrastructure, and external connectivity to national and global customers because of the scale economies for providers. Third, firms benefit from the superior flows of information and ideas in cities, promoting more learning and innovation. Proximity facilitates the communication of complex ideas between firms, research centers, and investors. Proximity also enables formal and informal networks of experts to emerge, which promotes comparison, competition, and collaboration. It is not surprising, therefore, that large cities are the most likely places to spur the creation of young high growth firms, sometimes described as “gazelles.” It is cheaper and easier to provide infrastructure and public services in cities. The cost of delivering services such as water, housing, and education is 30-50 percent cheaper in concentrated population centers than in sparsely populated areas.

The benefits of agglomeration can be offset by rising congestion, pollution, pressure on natural resources, higher labor and property costs; greater policing costs occasioned higher levels of crime and insecurity often in the form of negative externalities or agglomeration diseconomies. These inefficiencies grow with city size, especially if urbanization is not adequately managed, and if cities are deprived of essential public infrastructure. The immediate effect of dysfunctional systems, gridlock, and physical deterioration may be to deter private investment, reduce urban productivity, and hold back growth. Cities can become victims of their success, and the transformative force of urbanization can diminish.

The dramatic changes in the spatial form of cities brought about by rapid urbanization over the last two decades, present significant challenges and opportunities. Whereas new spatial configurations play a crucial role in creating prosperity, there is an urgent demand for more integrated planning, robust financial planning, service delivery, and strategic policy decisions. These interventions are necessary if cities are to be sustainable, inclusive, and ensure a high quality of life for all. Urban areas worldwide continue to expand, giving rise to an increase in both vertical and horizontal dimensions.

With cities growing beyond their administrative and physical boundaries, conventional governing structures and institutions become outdated. This trend has led to expansion not just in terms of population settlement and spatial sprawl, but has altered the social and economic spheres of influence of urban residents. In other words, the functional areas of cities and the people that live and work within them are transcending physical boundaries.

Cities have extensive labor, real estate, industrial, agricultural, financial and service markets that spread over the jurisdictional territories of several municipalities. In some cases, cities have spread across international boundaries plagued with fragmentation, congestion, degradation of environmental resources, and weak regulatory frameworks; city leaders struggle to address demands from citizens who live, work, and move across urban regions irrespective of municipal jurisdictional boundaries. The development of complex interconnected urban areas introduces the possibility of reinventing new mechanisms of governance.

A city’s physical form, its built environment characteristics, the extent and pattern of open spaces together with the relationship of its density to destinations and transportation corridors, all interact with natural and other urban characteristics to constrain transport options, energy use, drainage, and future patterns of growth. It takes careful, proper coordination, location and design (including mixed uses) to reap the benefits more compact urban patterns can bring to the environment (such as reduced noxious emissions) and quality of life.

Urban space can be a strategic entry point for driving sustainable development. However, this requires innovative and responsive urban planning and design that utilizes density, minimizes transport needs and service delivery costs, optimizes land- use, enhances mobility and space for civic and economic activities, and provides areas for recreation, cultural and social interaction to enhance the quality of life. By adopting relevant laws and regulations, city planners are revisiting the compact and mixed land-use city, reasserting notions of urban planning that address the new challenges and realities of scale, with urban region-wide mobility and infrastructure demands.

The need to move from sectoral interventions to strategic urban planning and more comprehensive urban policy platforms is crucial in transforming city form. For example, transport planning was often isolated from land- use planning, and this sectoral divide has caused wasteful investment with long-term negative consequences for a range of issues including residential development, commuting, and energy consumption. Transit and land- use integration is one of the most promising means of reversing the trend of automobile-dependent sprawl and placing cities on a sustainable pathway.

The more compact a city, the more productive and innovative it is and the lower it is per capita resource use and emissions. City planners have recognized the need to advance higher density, mixed-use, inclusive, walkable, bikeable, and public transport-oriented cities. Accordingly, sustainable and energy-efficient cities, low carbon, with renewable energy at scale are re-informing decision making on the built environment.

Despite shifts in planning thought, whereby compact cities and densification strategies have entered mainstream urban planning practice, the market has resisted such approaches, and consumer tastes have persisted for low-density residential land. Developers of suburbia and exurbia continue to subdivide the land and build housing, often creating single-purpose communities. The new urbanists have criticized the physical patterns of suburban development and car-dependent subdivisions that separate malls, workspaces and residential uses by highways and arterial roads. City leaders and planning professionals have responded and greatly enhanced new community design standards. Smart growth is an approach to planning that focuses on rejuvenating inner city areas and older suburbs, remediating brown-fields and, where new suburbs are developed, designing them to be town-centered, transit and pedestrian-oriented, less automobile-dependent and with a mix of housing, commercial and retail uses drawing on cleaner energy and green technologies.

The tension in planning practice needs to be better acknowledged and further discussed if sustainable cities are to be realized. The forces that continue to drive the physical form of many cities, despite the best intentions of planning, present challenges that need to be at the forefront of any discussion on the sustainable development goals of cities. Some pertinent issues, which suggest the need for rethinking past patterns of urbanization and addressing them include:

In reality, it is mainly these outer suburbs, edge cities and outer city nodes in larger city regions where new economic growth and jobs are being created and where much of this new population will be accommodated, if infill projects and planned extensions are not designed. While densification strategies and more robust compact city planning in existing city spaces will help absorb a portion of this growth, the key challenge facing planners is how to accommodate new growth beyond the existing core and suburbs. This will largely depend on local governments’ ability to overcome fragmentation in local political institutions, and a more coherent legislation and governance framework, which addresses urban complexities spread over different administrative boundaries.

Chapter 13 Global Environmental Issues and Sustainable Development for print only


The planet can only support so many people before natural resources begin to become depleted and cannot support human needs, called Earth’s carrying capacity for humans. Many geographers and other scientists believe that humans have grown beyond earth’s carrying capacity; a concept called overshooting. In less developed countries, this has occurred because of population growth; in more developed countries, it has to do with our consumption of natural resources. A natural resource is something found within the natural environment that is accessible and economically valuable to humans, including food, water, soil, plants, animals, and minerals. However, most resources are not renewable, and humans are either consuming them faster than the planet can replenish them or in the case of water and air are polluting them.

13.1 Depletion of Natural Resources

There are primarily two types of resources: energy and minerals. As noted, a natural resource only has “value” as long as humans need it. As it turns out, humans need more and more energy and mineral resources, resulting in increased costs. There has also been a steady rise in the cost of petroleum, gold, copper, platinum, and titanium.

Throughout history, most of the world’s energy came from animate power; the use of animals such as mules, ox, and horses. However, following the Industrial Revolution, most of the energy in Europe and the United States was used for machinery. The energy used to power the machinery came from inanimate power such as biofuel and fossil fuels. Currently, the most used energy source for less-developed nations is biofuels, such as trees, coal, and methane. However, in more developed nations and nations transitioning, fossil fuels have become the central source of energy.



The planet’s growing population has increased demands on natural resources, including forest products. Humans have been using trees for firewood, building homes, and making tools for millennia. Trees are a renewable resource, but deforestation occurs when they are removed faster than they can be replenished. Most people in rural areas in developing countries rely on firewood to cook their food. Many of these areas are experiencing a fast decline in the number of trees available. People living in mainly type B climates may not have access to many trees to start with; therefore, when trees are cut down for firewood or building materials, deforestation occurs. In the tropical areas, it is common for hardwood trees to be cut down for lumber to gain income or to clear the land for other agricultural purposes, such as cattle ranching. Countries that lack opportunities and advantages look to exploit their natural resources – in this case, trees – for either subsistence agriculture or economic gain. Deforestation has increased across the globe with a rapid rise in the worldwide population.

During the Industrial Revolution, European countries chopped down their forests at a rapid rate. Much of the British Isles was forested at one point, but today few forests remain on the British Isles, and they are typically protected. Colonialism brought the Europeans to the Americas. The United States, in its early development, pushed west from the original thirteen colonies, and many old-growth forests were cut down in the process. As railroad tracks were laid down and pioneer development pushed west into the Great Plains, where there were few trees, the great cutover occurred in the eastern and central forests – cutover is a term indicating the systematic deforestation of the eastern and central forests. Michigan and Wisconsin saw their trees removed in systematic deforestation.

Some areas were allowed to grow back, but many other areas were turned into farmland. Few old-growth forests remain in the United States. Today there are conflicts over how the timber industry is handling the forests in places such as the Pacific Northwest region of the United States.

Countries that are better off economically no longer have to cut down their trees, but can afford to substitute other resources or import lumber from other places. Developing regions of the world in Latin America, Africa, and parts of Asia are experiencing severe problems with deforestation. Deforestation is widespread: Residents of Haiti have cut down about 99 percent of the country’s forests; most of the wood has been used as fuel to cook food. People in Afghanistan have cut down about 70 percent of their forests. Nigeria has lost about 80 percent of its old-growth forests since 1990. Ethiopia has lost up to 98 percent of its forested acreage, and the Philippines has lost about 80 percent of its forests.

Brazil’s Amazon basin has undergone many projects that have driven deforestation. For example, about half the state of Rondônia in western Brazil has been deforested since 1990. The countries of Central America have lost about half their original forests, and deforestation continues on a systematic basis. Tropical regions of Southeast Asia and Africa are being exploited for their timber at unsustainable rates, causing deforestation that the next generation will have to address. India, with over a billion people, still has a high demand for firewood and building materials; their forests are declining faster than they can be replanted. China, with its billion-plus population, has been attempting to address its deforestation problems by implementing a massive replanting program and conservation measures. Other countries are starting to adopt similar measures.

Tropical rain forests only makeup about 5 percent of the earth’s surface but contain up to 50 percent of the earth’s biodiversity. These forests are cut down for a variety of reasons. Norman Meyers, a British environmentalist, estimated that about 5 percent of deforestation in tropical regions is caused by the push for cattle production. Nineteen percent of these forests are cut down by the timber industry, 22 percent are cut down for the expansion of plantation agriculture, and 54 percent are removed due to slash-and-burn farming. Most tropical rain forests are located in the Amazon basin of South America, in central Africa, and Southeast Asia. All these areas are looking for advantages and opportunities to boost their economies; unfortunately, they often target their tropical rain forests as a revenue source.

Deforestation causes more than the loss of trees for fuel, building materials, paper products, or manufacturing. Another related issue in the deforestation equation is soil erosion. Without the trees to hold the soil during heavy rains, soils are eroded, leaving the ground in an unproductive state. In tropical areas, soils are often degraded and lack nutrients. Most of the nutrients in the tropical areas rest in decaying material at the base of the trees that supply energy back into the ecosystem. Once the trees are removed, there is little replenishing of this energy supply. Soil erosion in tropical areas makes it hard for forests to grow back once they have been removed. Landslides can be a more severe component of the soil erosion problem. After heavy rainfall, entire hillsides saturated with water can slide downward, causing severe structural damage to buildings, homes, and agricultural plots. Tree roots help hold hillsides together and therefore help prevent landslides.

Forests play an essential role in the water cycle. Trees pull up moisture with their roots from the soil and transpire it through their leaves back into the atmosphere. Moisture in the atmosphere collects into clouds, condenses, and falls back to Earth. Not only do trees store water, but the organic matter at the base of the trees also stores water and makes it available to the broader ecosystem, which may slow down water runoff. Forest canopies disperse water during rainfall and create another layer of moisture in their leaves and branches, which either is used by other organisms or evaporates back into the atmosphere. Deforestation eliminates the role that forests play in the water cycle.

Forest ecosystems provide for a diverse community of organisms. Tropical rain forests are one of the most vibrant ecosystems on the planet. Their abundant biodiversity can provide insight into untapped solutions for the future. Plants and organisms in these habitats may hold the key to medical or biological breakthroughs, but wildlife and vegetation will be lost as deforestation eliminates their habitat and accelerates the extinction of endangered species.

Trees and plants remove carbon dioxide from the atmosphere and store it in the plant structure through the process of photosynthesis. Carbon dioxide is a significant greenhouse gas that is a part of the climate change process. Carbon dioxide and other similar gases reduce the amount of long-wave radiation (heat) that escapes from the earth’s atmosphere, resulting in increased temperatures on the planet. As more carbon dioxide is emitted into the atmosphere, climate change occurs. The removal of trees through deforestation results in less carbon dioxide being removed from the atmosphere, which contributes to climate change. Slash-and-burn farming methods that burn forests release the carbon in the plant life directly into the atmosphere, increasing the climate change effect.

Fossil Fuels

Everything that is or was alive is made out of carbon. Millions of years ago when the planet was a lot warmer, plant life was quite abundant. Over geologic time, these carbon bodies were buried and ultimately converted to fossil fuels (i.e., coal, petroleum, and natural gas). When you fill your car up at the gas station, you are technically putting ancient plant life into your vehicle. When you drive off, that fuel is burned, and the ancient carbon is released into the environment in the form of carbon dioxide.

There are two concerns about fossil fuels. One is that the carbon dioxide released is a greenhouse gas, and the other is that it is considered a finite resource. A natural resource is considered a renewable resource if nature can reproduce it within a human lifetime. So energy sources such as solar energy, wind power, and geothermal are considered renewable energy sources. Fossil fuels are not considered renewable because it requires millions of years for the earth to replenish them. So ultimately, humans will run out of fossil fuels, but the question is when. In terms of coal, the world has well over 200 years worth, but with petroleum, the question becomes more complicated.

Currently, there are over a trillion barrels of petroleum, called proven reserves, that we are aware of with current technology. Potential reserves are resources of petroleum not discovered yet by society. Currently, there is much concern about how many reserves of petroleum are left to discover. Technology today is allowing the industry to discover reserves deeper than ever before and tap into petroleum reserves in ways never allowed before.

Uneven Distribution

Another global problem in terms of fossil fuels is that it is not found uniformly around the planet. Coal forms in tropical regions where there are lots of vegetation and swamps. As the vegetation falls into oxygen-poor water, it is converted into a carbon-based rock over geologic time. Because of plate tectonics, the slow movement of continents around the planet, most of the mid-latitude countries such as China, Russia, and the United States were located near the equator 250 million years ago. Today these countries have abundant amounts of coal. Petroleum and natural gas forms on the ocean floor under high pressure from overlying water and sediment. Some of these areas are still underwater, such as in the Persian Gulf and the Gulf of Mexico. Other regions are no longer underwater such as the Middle East.

Most of the world’s sources of fossil fuels exist in more developed countries, which has much helped in their development. Today the United States and China are the largest consumers of fossil fuels on the planet. In the 21st century, the demand for coal, petroleum, and natural gas will shift to less-developed nations as they move through the demographic transition model.

The majority of the world’s petroleum prices is determined by As noted earlier, mid-latitude countries such as the United States, Russia, and China have the most abundant supply of coal. In terms of petroleum, the mission of the Organization of Petroleum Exporting Countries (OPEC) “is to coordinate and unify the petroleum policies of its Member Countries and ensure the stabilization of oil markets in order to secure an efficient, economic and regular supply of petroleum to consumers, a steady income to producers and a fair return on capital for those investing in the petroleum industry.”

In the 1970s, there was a global energy crisis. This occurred when Arab countries of OPEC were angered by Europe and the United States’ support over Israel during the 1973 war with Egypt, Jordan, and Syria. The Arab OPEC members refused to supply oil to the United States, which immediately created a fuel shortage. During the 1980s and 1990s, prices of oil dropped dramatically, stimulating global economies all around the world. After the fall of the Soviet Union, Russia struggled to survive as a modern society. However, starting in the late 1990s, Russia began exporting its petroleum and coal resources and its political, economic, and military power grew substantially. Cheap fuel in the United States spurred the automotive industry to build large SUVs with low miles-per-gallon. However, the mid-2000s saw a sharp increase in fuel prices with record prices occurring in the summer of 2008. Following the summer of 2008, SUV sales plummeted risking the possibility of Ford and GM becoming extinct.

Nonrenewable Substitutions

With the increase of oil in the last few years, there has been a desire to find alternatives. There have been a sharp increase in natural gas vehicles because natural gas is cheaper and pollutes less than oil. However, the underlying economics of supply and demand state that as natural gas is used more (demand), the cost is likely to follow.

Since the world has plenty of coal to last hundreds of years, some have pushed more coal burning. There are several environmental concerns with coal. First, coal is the “dirtiest” fossil fuel in terms of air pollution. Burning coal releases vast amounts of sulfur, which creates acid rain and mercury, which damages our neurological system. It also releases the most substantial amount of carbon dioxide, which is a greenhouse gas. With the current concern with global warming, there have been many talks about carbon sequestration. The idea behind this is that if humans can capture the carbon dioxide before it is released, we might be able to “lock” it deep within the earth and thus preventing it from contributing to global warming. However, the technology here is far from proven yet.

The third source of nonrenewable energy is nuclear. Since Chernobyl in 1986 in the former Soviet Union and the Three-Mile Island incident in the United States, our country has been very apprehensive in creating new nuclear power plants. The benefit of nuclear power is that incredible amounts of energy can be generated without polluting the environment. There are serious concerns about potential accidents and the radioactive waste it generates. There has been a recent heated debate in the West as to where to store radioactive waste. In Utah, there have been conversations regarding the storing of nuclear waste at the Goshute Indian Reservation as a short-term stop to Yucca Mountain in Nevada. However, many in Utah believe that a nuclear waste, which takes tens of thousands of years to decompose, in Utah will never leave even though we do not have a nuclear power plant. In Nevada, there is concern about the actual safety of storing nuclear waste in a mountain with nearby fault lines. Moreover, after the September 11 terrorist attacks, there is renewed interest in nuclear power plants becoming targets.

Natural Substitutes

With the increase of oil in the last few years, there has been a desire to find alternatives. There have been a sharp increase in natural gas vehicles because natural gas is cheaper and pollutes less than oil. Basic economics of supply and demand state that as natural gas is used more (demand), the cost is likely to follow.

Since the world has plenty of coal to last hundreds of years, some have pushed more coal burning. However, there are several environmental concerns with coal. First, coal is the “dirtiest” fossil fuel in terms of air pollution. Burning coal releases vast amounts of sulfur, which creates acid rain and mercury, which damages our neurological system. It also releases the most significant amount of carbon dioxide, which is a greenhouse gas. With the current concern with global warming, there have been many talks about carbon sequestration. The idea behind this is that if humans can capture the carbon dioxide before it is released, we might be able to “lock” it deep within the earth and thus preventing it from contributing to global warming. However, the technology here is far from proven yet.

The third source of nonrenewable energy is nuclear. Since Chernobyl in 1986 in the former Soviet Union and the Three-Mile Island incident in the United States, our country has been very apprehensive in creating new nuclear power plants. The benefit of nuclear power is that incredible amounts of energy can be generated without polluting the environment. However, there are serious concerns about potential accidents and the radioactive waste it generates. There has been a recent heated debate in the West as to where to store radioactive waste. In Utah, there has been talking of storing nuclear waste at the Goshute Indian Reservation as a short-term stop to Yucca Mountain in Nevada. But many in Utah believe that a nuclear waste, which takes tens of thousands of years to decompose, in Utah will never leave even though we do not have a nuclear power plant. In Nevada, there is concern about the actual safety of storing nuclear waste in a mountain with nearby fault lines. Moreover, after the September 11 terrorist attacks, there is renewed interest in nuclear power plants becoming targets.

13.2 Environmental pollution

Pollution of the environment occurs when humans contaminate the air, water, or land. Pollution can also be broken down into two categories: primary and secondary. Primary pollution is when humans directly contaminate the earth in some manner. Examples include mercury, sulfur, and even carbon dioxide. Secondary pollution happens when a primary pollutant reacts with another primary pollutant, sunlight, and water to create a different pollutant.

An example is acid rain. Sulfur dioxide is a primary pollutant, but when it reacts with precipitation is becomes a secondary pollutant called acid rain. One of the biggest problems with pollution is that those who pollute are usually not the ones affected by it; instead, the down-winders are.

Air Pollution

The atmosphere is mostly made of 78 percent nitrogen, 21 percent oxygen, and small percents of other trace molecules such as ozone, carbon dioxide, water vapor, and aerosols. Air pollution occurs when humans add unnatural substances into the atmosphere. Most of the air pollution from the industry comes from coal, while automotive pollute vast amounts of ozone, carbon dioxide, and sulfur into the atmosphere. However, in the 1970s, the United States created the Clean Air Act, which has dramatically enhanced the quality of our nation’s air. Check out this video from National Geographic on the world’s air quality.

Those who pollute are usually not the ones affected by it. Industrialization in eastern North American and eastern Europe have generated large-scale pollutants such as sulfur oxides and nitrogen oxides through the burning of fossil fuels. When these pollutants react with water, they form acid precipitation. Acid precipitation can cause large-scale damage to aquatic life and forests by making the vegetation very sick and dying. In forests, this can lead to disease through pest infestation. Acid precipitation can also damage or destroy buildings and monuments made out of marble such as tombstones.

Ozone Hole

In the 1920s, humans developed a chemical called chlorofluorocarbons (CFCs) for things such as refrigerating and air conditioners. However, in the 1970s, two American scientists discovered that these CFCs were weakening the ozone hole. What they learned is that when the CFC’s reach the layer of the ozone hole, the ultraviolet radiation from the sun breaks the chlorine off which can attach and destroy over 100,000 ozone molecules and continue in the upper atmosphere for over 100 years. Over time and much debate, the world got together and signed the Montreal Protocol in 1987 to phase out CFCs. Today, most industrialized countries have eliminated the use of CFCs, but the ozone hole is not required to heal for another 50-100 years. Learn more about what is currently going on with the ozone hole at NASA’s Ozone Hole Watch.

Water Pollution

Water is the most valuable resource on the planet, but humans keep polluting it in various ways. Manufactures use water to create and process food. Farmers pollute vast amounts of water through fertilizer and waste from pigs and cows in unhealthy feedlots. Water is used by coal powerplants to extract and wash coal, along with cooling the steam used to make electricity. All of these processes, along with residential use, have negative impacts on water quality.

Water pollution can significantly harm aquatic life in rivers, lakes, and the ocean. Many of the fertilizers in farmers and the cleaners we use can create algae blooms in our local rivers. When the algae die, it can also remove the oxygen from the water, which can kill fish and other aquatic life. These are called dead zones, and one of the biggest in the world is forming in the Gulf of Mexico because of the pollution in the Mississippi River. Just like our air, the nation’s water has dramatically improved since the 1970s because of the Clean Water Act.


13.3 Renewable resources

Humans cannot sustain the path we have been traveling with our consumption of resources, and a global population expected to peak at 9 billion by 2050. We need to learn how to live differently without decreasing our quality of life. One such possibility is to move towards a renewable energy economy. The following are the diverse types of renewable energy.


Biomass is when humans burn vegetation as a fuel source. Many argue that this not a viable option for human energy consumption. Burning biomass releases large amounts of carbon dioxide into the atmosphere and requires the destruction of ecosystems such as deforestation. There has also been a recent push for ethanol as a “green” source of energy. In the United States, corn has been used and subsidized to make ethanol. The effects have been a spiraling rising in the cost of corn-based food. Plus many would argue that humans should not be using food for fuel when humans are now consuming more food than we are producing. In Brazil, they are using sugarcane to produce ethanol. Because there is much money to be made in the ethanol industry, Brazil is cutting down the Amazon rainforest to produce more sugarcane for its energy economy. So it can be argued that ethanol is not “green” energy if it requires deforesting the rain forests along with causing food prices to rise.

Hydroelectric Power

Hydroelectric power is also questionable as an energy source even though it is renewable. Hydroelectric power requires dams being built in order for flowing water to turn turbines within the dam to generate electricity. There are numerous problems with power coming from hydroelectric dams. It requires flooding usable and often time fertile land to create a lake. Over time, the lake can fill up as sediment gets deposited into the lake. Dams can also harm aquatic wildlife such as salmon because they prevent them from returning to their spawning locations. Many northwestern states in American have dismantled damns because salmon are near extinction. However, it must be said that it is “clean” energy in that hydroelectric power does not pollute the air or water.

Wind Power and Geothermal Energy

Windmills have been around for hundreds of years, but only recently have they been used to generate electricity. Until last year, wind power was the fastest-growing energy source in the world. Moreover, with the rising costs of fossil fuels, wind power is now cheaper to produce than energy from fossil fuels. Farmers are getting onboard with wind power because power companies will rent space to place the windmills, which will provide a steady income for the farmer. However, the farmer can still grow their crops or have their cattle and maintain their way of life. The energy created by wind is similar to dams because the wind turns the blades, which turns a turbine within the windmill to generate electricity.

There are a few concerns with wind power, however. Some do not like how windmills look because they require being out in the open; whereas coal power plants are easier to hide behind mountains. There is also concern that windmills can harm migratory birds and bats. However, wildlife is more likely to be hurt by changing climates than by small-scale windmills. Now out in Europe, they have been earnest about wind power. Some of the windmills along the continental shelf, where the winds are steadily consistent, have windmills so giant they can land a helicopter on them. They are so large that each blade is over 300 feet long (said another way, each blade is taller than the Statue of Liberty). The United States is still far behind other countries in Europe, but that is starting to change. It is now possible to purchase wind power from various energy companies. The most extensive wind power program in the United States is called the Blue Skies Program by Rocky Mountain Power.

The Earth’s interior is still sweltering because of Earth’s formation. A new technique being implemented is to use water and the internal heat the earth to produce steam, which can turn turbines to generate electricity. It requires using existing groundwater or pumping groundwater into the earth so the heat can evaporate the water into steam and turn a turbine. The image below is a geothermal plant in Iceland where they plan to use the heat from their volcano (Iceland is a volcanic island) to power their entire country.

Solar Energy

With the sun still having 5 billion years of life, our star is the ultimate renewable energy source. There are two types of solar energy: passive and active. Passive solar energy requires no special devices, rather south-facing windows and dark surfaces to light and heat buildings. This is a very inexpensive alternative, and, surprisingly, it is not used more often. Active solar energy captures heat and generates electricity by using photovoltaic cells with solar panels. The panel’s cells are made from silicon, which is the second most abundant mineral on Earth’s crust and when combined with other materials become sensitive to sunlight, called the photovoltaic effect. The electrons within the cells move through the silicon and produce an electrical current. In 2008 solar panels surpassed windmills as the fastest-growing energy source in the world.


There has also been a steady demand to recycle rather than through products into our landfills. However, recycling is not only about saving landfill space; it is about water, natural resources, and energy. It requires less energy, water, and natural resources from the earth to re-create something than to mine and process the raw material. Take a soda can. How long do you keep a soda can once you open it? Did you know that it may take up to three years for the material to be mined from the mountain, processed, shipped, filled with soda, and shipped to you? This requires a lot more energy than we typically consider, and learning to recycle projects does more than just savings than just landfill space.

There is now a variety of ways someone can recycle. Many cities around the nation have curbside recycling. There are also several drop-off sites, which are often found at retail and grocery stores. Buy-back centers are commercial businesses that purchase recyclable goods. However, it is important to note that what you can recycle varies based on the recycling company. Therefore citizens must learn what products can be recycled for your geographic area.

13.4 Sustainable Development Goals

Sustainable Development Goals

The ideas behind sustainable development can be traced back to early works of scholars such as Rachel Carson’s Silent Spring (1962), Garret Hardin’s Tragedy of the Commons (1968), and Paul Ehrlich’s Population Bomb (1971). Despite different focuses of these classic works related to population and environment, all raised public concerns over environmental problems from human activities and highlighted the importance of systems thinking.

Some tremendous efforts and notable achievements have been made towards sustainable development but are our contemporary civilization sustainable? It turns out that in many ways, it is not. The basic idea of unsustainable development is that there are some things that we are doing today that we cannot continue doing forever. Much of our development depends on natural resources that either cannot be replaced or that are not being replaced as fast as we are depleting them. Some major examples are:

Each of these resources is becoming increasingly scarce. We cannot continue using them as we do today. Either we will need to shift away from them on our own, or shortages will force us to change our ways.

There are other reasons why some aspects of contemporary development may be considered unsustainable. Development is changing the global climate system and affecting biodiversity in ways that could have very perilous consequences. We need to note that if we try to continue with development as we have been, then the ensuing changes to climate and biodiversity could eventually prevent us from maintaining our state of development. Finally, as we saw on the previous page, development even today is not necessarily something to be desired. On the other hand, development involves much of what is important to us and thus is not something we can easily walk away from. Achieving development that is both desirable and sustainable is an important goal for our lives and our society.

Private: Appendix

This is where you can add appendices or other back matter.