This Document Contains Chapters 1 to 2 Chapter 1 Understanding Earth: A Dynamic and Evolving Planet Chapter Outline 1.1 Introduction 1.2 What Is Geology? 1.3 Geology and the Formulation of Theories 1.4 How Does Geology Relate to the Human Experience? 1.5 How Does Geology Affect Our Everyday Lives? 1.6 Global Geologic and Environmental Issues Facing Humankind 1.7 Origin of the Universe and Solar System, and Earth’s Place in Them GEO-INSIGHT 1.1: Mars—The “Red Planet” 1.8 Why Earth Is a Dynamic and Evolving Planet 1.9 The Rock Cycle 1.10 Organic Evolution and the History of Life 1.11 Geologic Time and Uniformitarianism 1.12 How Does the Study of Geology Benefit Us? Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Geology is the study of Earth and also planets and moons in our solar system. • Earth is a complex system of interconnected components that interact and affect one another in various ways. • Theories are based on the scientific method and can be tested by observation or experiment. • Geology plays an important role in human experience and affects us as individuals and societies. • Global warming from human activities has already begun to impact the planet. • The universe is thought to have originated approximately 14 billion years ago with a big bang. The solar system and planets evolved from a turbulent, rotating cloud of material surrounding the embryonic Sun. • The solar system began in a solar nebula in which the Sun and planets, including Earth, formed. • Earth consists of three concentric layers—core, mantle, and crust—and this orderly division formed during Earth’s early history. • Plate tectonics is the unifying theory of geology and this theory revolutionized the science. • The rock cycle illustrates the interrelationships between Earth’s internal and external processes and shows how and why the three major rock groups are related. • The theory of organic evolution provides the conceptual framework for understanding the history of life. • An appreciation of geologic time and the principle of uniformitarianism is central to understanding the evolution of Earth and its biota. • Geology is an integral part of our lives. Chapter Summary • Earth can be viewed as a system of interconnected components that interact and affect one another. The principal subsystems of Earth are the atmosphere, hydrosphere, biosphere, lithosphere, mantle and core. Earth is a dynamic planet that continually changes because of the interactions among its various subsystems and cycles. Earth is a continually changing and dynamic planet because of the interactions among its various subsystems and cycles. • Geology, the study of Earth, is divided into (1) physical geology, which is the study of Earth materials and the processes that operate both within Earth and on its surface; and (2) historical geology, which examines the origin and evolution of Earth, its continents, oceans, atmosphere, and life. • The scientific method is an orderly, logical approach that involves gathering and analyzing facts about a particular phenomenon, formulating hypotheses to explain the phenomenon, testing the hypotheses, and finally proposing a theory. A theory is a testable explanation for some natural phenomenon that has a large body of supporting evidence. • Geology is not only part of the human experience, examples of which can be found in art, music, and literature, but it also affects our daily lives as individuals, societies, and nation-states. A basic understanding of geology, and science in general, is critical for dealing with and finding solutions to the many environmental problems and issues facing humankind. • The universe began, in what is popularly called the Big Bang, approximately 14 billion years ago. Astronomers have deduced this age by observing that celestial objects are moving away from each other in an ever-expanding universe. Furthermore, the universe has a pervasive background radiation of 2.7 K above absolute zero (2.7 K = –270.3°C), which is thought to be the faint afterglow of the Big Bang. • About 4.6 billion years ago, our solar system formed from a rotating cloud of interstellar matter. As this cloud condensed, it eventually collapsed under the influence of gravity and flattened into a counterclockwise-rotating disk. Within this rotating disk, the Sun, planets, and moons formed from the turbulent eddies of nebular gases and solids. • Earth formed from a swirling eddy of nebular material 4.6 billion years ago, accreting as a solid body and soon thereafter differentiating into a layered planet. • Earth’s outermost layer is the crust, which is divided into continental and oceanic portions. The crust and underlying solid upper mantle, together known as the lithosphere, overlie the asthenosphere, a zone that behaves plastically and flows slowly. The asthenosphere is underlain by the solid lower mantle. Earth’s core consists of an outer liquid portion and an inner solid portion. • The lithosphere is divided into a series of plates that diverge, converge, and slide sideways past one another. • Plate tectonic theory provides a unifying explanation for many geologic features and events. The interaction between plates is responsible for volcanic eruptions, earthquakes, the formation of mountain ranges and ocean basins, and the recycling of rock materials. • The three major rock groups are igneous, sedimentary, and metamorphic. Igneous rocks result from the crystallization of magma or the consolidation of volcanic ejecta. Sedimentary rocks are typically formed by the consolidation of rock fragments, precipitation of mineral matter from solution, or compaction of plant or animal remains. Metamorphic rocks result from the alteration of other rocks, usually beneath Earth’s surface, by heat, pressure, and chemically active fluids. • The rock cycle illustrates the interactions between Earth’s internal and external processes and how the three rock groups are interrelated. • The central thesis of the theory of organic evolution is that all living organisms evolved (descended with modifications) from organisms that existed in the past. • Time sets geology apart from the other sciences except astronomy, and an appreciation of the immensity of geologic time is central to understanding Earth’s evolution. The geologic time scale is the calendar geologists use to date past events. • The principle of uniformitarianism is basic to the interpretation of Earth history. This principle holds that the laws of nature have been constant through time and that the same processes operating today have operated in the past, although not necessarily at the same rates. • Geology is an integral part of our lives. Our standard of living depends directly on our consumption of natural resources, most of which formed millions and billions of years ago. Enrichment Topics Topic 1. Climate Change. One of the major issues facing young people in their lives will be global warming. While climate has changed in Earth’s past, and has been warmer than even the most dire predictions for how temperatures will increase over the next few centuries, it is human systems that depend on climate being more-or-less constant and predictable. Some of the systems we depend on that could change include the following. • The major agricultural areas could become too dry and hot to grow food. Moving agriculture closer to higher latitudes has political and environmental ramifications. For example, what if the American bread basket moves into Canada. What does that mean for the U.S.? Also, good soils must build up over decades and centuries. Just because the climate becomes favorable for agriculture in a more northern location does not mean that the soils will also be good. Many of the world’s people rely on subsistence agriculture, in which they grow enough food to meet their family’s needs and not much more. Harshening environmental conditions will damage the ability for many of these people to survive. • Many people live in coastal areas, and much of society’s infrastructure is concentrated near coastlines. Sea level rise will cost millions of people their homes. In low-lying Florida, a one-foot rise in sea level, which could happen by the end of the century, will result in the loss of 100 feet of beaches. Communities are already having trouble protecting their homes and businesses, particularly during storms, and the situation will just get worse. • Ecosystems are adapted to the climate conditions in which they evolved. Humans have restricted many of those ecosystems to certain areas, such as national parks. For example, the remaining redwood trees are found in national and state parks in California. If temperature and precipitation conditions become unfavorable, the redwoods in the park would die off but there is little undeveloped land for new forests to grow. Also, rising sea level will drown many coastal ecosystems, such as mangrove forests and coral reefs. These are important ecosystems for seafood sources and for coastal protection. Topic 2. Scale of the Solar System. Use a football field analogy to convey to students the size of the solar system and relative proximities of the planets to the Sun. Put the Sun on the goal line. Mercury is on the 1 foot line Venus is on the 2 foot line Earth is on the 1 yard line Mars is on the 1 1/2 yard line Jupiter is on the 5 yard line Saturn is on the 10 yard line Uranus is on the 20 yard line Neptune is on the 30 yard line Pluto is on the 40 yard line. On this same scale, the nearest star would be 500 miles away. Topic 3. Faith versus Science. Science serves some of the same purposes that religion does. Science explains the way the world works, for example. But science is different from religion because science is based on things that are testable. You can do an experiment to see if something in science is correct. Still it is necessary to have faith in a few things in science. For example, we must have faith that the world is as we perceive it and that we are capable of understanding it. Science cannot address matters of faith. Since there is no scientific way to validate the supernatural, faith in the supernatural is not the same as a scientific theory or hypothesis Common Misconceptions Misconception 1. Geology is less scientific than physics or chemistry. Fact: A science is distinguished by its methodology. Geology uses the scientific method in investigating questions about Earth (and other bodies in the universe such as the Moon and other planets). Although many geologic studies cannot be conducted under the tightly controlled conditions of a laboratory, but must be examined in the outside world, they are nonetheless approached in a strictly scientific way. Misconception 2: A theory is “just” a theory. It is not highly regarded by all scientists. Fact: A theory is as good as it gets in science. A law is a statement about something that happens all the time, every time; like the law of gravity explains what will happen if you release a coin held above the ground. A theory is an explanation of a complex set of phenomena. It is accepted by virtually all scientists and there is no major evidence that refutes it. The Theory of Evolution and the Theory of Plate Tectonics are both major frameworks on which most observations (field and experimental) in the biological and earth sciences rest. Neither science would make sense in the modern world without those theories. Lecture Suggestions 1. Have the students look around the classroom for mineral substances (metal and plastic furniture, cement block or sheetrock walls, floors with vinyl tile or synthetic carpet, glass in light fixtures and windows). They should also keep in mind that mineral fuels are used for heating, lighting, and air-conditioning. Even natural fibers and materials in students' clothing (wool, cotton, silk, leather) depend on proper soil and the availability of fresh water. 2. Almost every day there are stories in the newspapers and on radio and television that are relevant to geology—about volcanic eruptions, earthquakes, floods, landslides, subsidence or collapse of old mines, water quality, pollution, waste (especially toxic) disposal. Start a file of these clips and introduce them at the appropriate places in the course. It can be very effective to display a printed article as you discuss that article. Or suggest that students bring in articles they come across or summaries of information from newscasts. 3. Ask the students if they can explain how a flipping a light switch makes light. We depend on science, yet the average person doesn't really understand how simple, long-existing technologies work. Discuss how many other things are common in everyday life but might be considered “magic.” 4. Point out ways in which people employ the scientific method in drawing conclusions in their daily lives. Extract from these examples the elements and sequence of thought embodied by the scientific method. What are the facts? What is the explanation? Contrast this method with conclusions based on the supernatural. Where does faith come in? Is faith important in science? If so, where? 5. Point out that broad conclusions that are arrived at via the scientific method and are relied upon in daily life are equivalents of a “scientific theory of (individual) human experience.” For example, one cannot safely stroll into the midst of moving traffic. 6. Demonstrate with an everyday example (e.g., a road-kill, the event being unseen, but its result later observed) that the scientific method can be used to construct hypotheses about events that have not been directly observed. Stress that the lack of opportunity to observe historical events in geology is more of an apparent, than a real, problem. There are many ways that scientists can use scientific method to infer past events: using radiometric dating to determine the age of a material, for example. Although particular historical events have only happened once, the class of events to which each belongs (e.g., mountain building) is represented by thousands of individual events, each of which can serve as either data or a test of a hypothesis or theory. 7. Clearly contrast the popular use of the term “theory” (meaning speculation, guess, or conjecture) with the legitimate scientific use of the term. Come up with some fun examples of how the word is misused in everyday language. For example, “My theory on why she dumped him is that he doesn’t drive a nice car.” Correctly speaking, that would be a hypothesis! 8. Teach students what a planet is by discussing why Pluto is no longer considered a planet. Encourage a class discussion on whether Pluto should regain its planetary status or remain as a lesser “dwarf planet.” 9. As Thomas Kuhn has proposed, plate tectonic theory represents perhaps the clearest example of how a reigning theory is questioned and is eventually discarded for another. In particular, emphasize the largely descriptive nature of geology and its hypotheses prior to plate tectonic theory as an analogy to the initial and latter stages of the scientific method. A discussion of plate tectonic theory could aid in illustrating the nature of the scientific method, the development of scientific theories, and the day-to-day business of doing science, as well as the elements and history of the theory itself. However, you may want to postpone this discussion until Chapter 2: Plate Tectonics: A Unifying Theory. 10. Emphasize the contrast in physical properties between the lithosphere and the asthenosphere and how these determine the behavior of plates. 11. The rock cycle is really the rock recycle: any rock can become any other type of rock. The rock cycle is a description of the processes by which rocks and materials (such as magma or sediments) are endlessly transformed from one state to another. 12. When covering the principle of uniformitarianism, ask a number of students to each give one example of this principle drawn from their daily experience. 13. Illustrate the importance of natural resources to societies with an example of a war that was fought over natural resources or a society that failed due to a shortage of natural resources. Examples might include the Persian Gulf War, African wars fought for diamonds, and the failure of the society on Easter Island due to loss of resources. Consider This 1. Why is plate tectonics a theory and not a fact? Answer: Plate tectonics is a theory because it is a well-substantiated explanation based on extensive evidence, including geological, seismic, and geophysical data. However, in scientific terms, a "theory" represents a comprehensive framework that can be tested and refined, while "fact" refers to observable phenomena. The theory of plate tectonics helps explain how Earth's lithosphere is divided into plates that move and interact, shaping the planet's surface. 2. Why is plate tectonics called the unifying theory of geology? How could the distribution of volcanoes, earthquakes, mountain ranges, and mineral deposits be explained without it? Answer: Plate tectonics is called the unifying theory of geology because it provides a comprehensive framework that explains the distribution and formation of volcanoes, earthquakes, mountain ranges, and mineral deposits by linking them to the movement of Earth's lithospheric plates. Without it, these geological features would appear as isolated phenomena, with no coherent explanation for their patterns and relationships, leading to fragmented and less accurate models of Earth's processes. 3. Why can the rock cycle be considered a part of plate tectonics? Does the fact that the rock cycle involves the hydrologic cycle and atmospheric processes separate it from plate tectonics? How are hydrologic and atmospheric processes also a part of plate tectonics? Answer: The rock cycle is part of plate tectonics because tectonic processes drive the formation, destruction, and transformation of rocks through processes like volcanism, mountain-building, and subduction. While the rock cycle involves the hydrologic and atmospheric cycles, these are interconnected with plate tectonics as tectonic activity influences weathering, erosion, and sediment transport. Thus, plate tectonics provides the underlying framework that integrates these cycles into a cohesive system. 4. How would understanding earth history be different without the principle of uniformitarianism? Answer: Without the principle of uniformitarianism, which states that geological processes operate similarly over time, understanding Earth’s history would be fragmented and less coherent. This principle allows geologists to interpret past events based on current processes, providing continuity and consistency in reconstructing Earth's history. Without it, explaining ancient geological formations and their evolution would rely more on speculation and less on observable, repeatable processes. 5. Students are very likely to have had little or no exposure to the theory of organic evolution. Explaining the theory carefully and with lots of evidence to back it up is extremely important for the understanding of science by these citizens, future parents, school board members, and book buyers. Answer: The theory of organic evolution, primarily formulated by Charles Darwin, proposes that species evolve over time through natural selection, where advantageous traits become more common in a population. This theory is supported by extensive evidence from fossils, genetic studies, and observed evolutionary changes in organisms. Understanding evolution is crucial as it underpins modern biology, informs conservation efforts, and shapes scientific literacy. 7. What properties make Earth habitable while the other planets in our solar system are not? Answer: Earth is habitable due to its liquid water, stable climate, suitable atmosphere, and magnetic field. These conditions are a result of its optimal distance from the Sun, diverse atmospheric composition, and geothermal activity. In contrast, other planets lack these conditions, leading to extreme temperatures, hostile atmospheres, or lack of liquid water, making them inhospitable for life as we know it. Important Terms principle of uniformitarianism geologic time scale fossils organic evolution metamorphic rocks sedimentary rocks igneous rocks rock cycle minerals rock plate tectonic theory crust plates lithosphere asthenosphere mantle core Jovian planets terrestrial planets solar nebula theory Big Bang hypotheses scientific method theory geology system Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Geology.com http://geology.com/ Geology articles and news including information about careers in geology, a highly paid profession. 2. The Grand Canyon Suite by Ferde Grofe is a good example of geology-inspired art. You can listen to it here: http://www.emusic.com/album/Erich-Kunzel-Grofe-Grand-Canyon-Suite-Gershwin-Catfish-Row-MP3-Download/11156792.html 3. Introduction to the Nine8 Planets http://nineplanets.org/ This longstanding website presents information on the objects of our solar system, focusing on scientific knowledge, but also the history and mythology. 4. Earth Observatory http://earthobservatory.nasa.gov/ This site is the portal to satellite images of Earth from space and focuses on natural processes and also the visible changes due to those processes or human influences. 5. Smithsonian: This Dynamic Earth http://www.mnh.si.edu/earth/ Introductory geology presented in a multimedia format. 6. Real Climate http://www.realclimate.org Real news about climate change by real climate scientists. 7. Intergovernmental Panel on Climate Change http://ipcc.ch/ Every few years the IPCC issues a report that is the work of many scientists who work on the issue of climate change. This report is highly regarded by scientists, politicians, and journalists. 8. Pew Center on Climate Change http://www.pewclimate.org Climate change news and politics at the state, federal and international levels. Videos 1. Earth: The Biography, BBC, DVD (2008, 230 mins.) Satellite images and computer graphics show some of Earth’s most remarkable features. 2. Nature of Earth: An Introduction to Geology. The Teaching Company, DVD (2006, series of 36 thirty-minute lectures) The drama of geology is all around you. 3. Planet Earth – The Complete BBC Series. Discovery, DVD (2007, 550 mins.) An 11-part series of different environments and the living creatures and inhabit them, narrated by David Attenborough. 4. The Geology of the United States. Insight Media, DVD (1995, 20 mins.) The principle landforms and physiographic provinces of the U.S. 5. The Universe, Collectors Set, HISTORY, DVD(2009; 33 hours, 41 mins.) Computer graphics and animation, NASA images and scientific information meld together in this exploration of the universe. 6. Geography Resources: Introducing Mapping Concepts. Insight Media, DVD (2004, 25 mins.) Principles of maps and mapping including the use of the Global Positioning System. 7. Geologic Maps: Portraits of the Earth. Insight Media, DVD (2005, 20 mins.) An introduction to what geologic maps depict. 8. Journey to the Edge of the Universe, National Geographic, DVD (2009, 91 mins.) Travel through the universe in a single unbroken image by the Hubble Space Telescope. 9. The Planets, New Video Group DVD (1999, 400 mins.) A guided journey through the solar system using NASA footage. 10. Wonders of the Solar System, BBC Warner, DVD (2010, 300 minutes) Some of the most amazing features of our solar system using the latest scientific knowledge and images. 11. An Inconvenient Truth DVD (2006, 96 mins.) Vice President Al Gore’s Academy Award winning 2006 documentary of global warming and its potential effects on our planet. 12. Warnings from the Ice, NOVA PBS DVD (2008, 56 mins.) Antarctic ice sheets yield evidence of how the planet is warming. 13. Global Warming: The Rising Storm, Ambrose Video Pub., Inc. DVD (2007, 114 mins.) The effects of global warming on the planet that are already being seen. 14. Global Warming: Science and Solutions, Ambrose Video Pub., Inc. DVD (2006, 116 mins.) Possible solutions to the planet’s rising temperatures. 15. Miracle Planet, Ambrose Video Pub., Inc. DVD (2006, 248 mins.) Earth’s amazing evolution over more than 4 billion years. 16. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #1: Down to Earth. Annenberg/CPB Collection Comparisons of Earth with Venus and Mars. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 1.3 Every year the life expectancy of the average American increases as well as our usage of minerals, metals, and fuels needed over a lifetime to maintain our standard of living. Is this increase sustainable, and is there anything that can be done to balance the depletion of natural resources but still maintain a high standard of living? How does our increasing consumption of these natural resources impact the rest of the world’s population? Answer: Although population growth in undeveloped countries threatens sustainability of natural ecosystems and resource use, over-consumption in developed countries may pose a more serious problem. At least part of the rise in global consumption is the result of population growth. The U.N. projects that world population will increase 41 percent by 2050, to 8.9 billion people, with nearly all of this growth in developing countries. This surge in human numbers threatens to offset any savings in resource use from improved efficiency, as well as any gains in reducing per-capita consumption. Even if the average American eats 20 percent less meat in 2050 than in 2000, total U.S. meat consumption will be 5 million tons greater in 2050 due to population growth. The United States, with less than 5 % of the global population, uses about a quarter of the world’s fossil fuel resources—burning up nearly 25 % of the coal, 26 % of the oil, and 27 % of the world’s natural gas. As of 2003, the U.S. had more private cars than licensed drivers, and gas-guzzling sport utility vehicles were among the best-selling vehicles. New houses in the U.S. were 38 % bigger in 2002 than in 1975, despite having fewer people per household on average. ❯❯ Critical Thinking Question Figure What types of geologic events would cause interruptions to the idealized cycle shown on the margin of the rock cycle? What do you think is more common and why—completion of an idealized cycle, or one in which there are interruptions? Answer: Interactions between plates through plate tectonics can interrupt the circular ideal of the rock cycle. In a sense, the interruptions are the norm rather than the ideal. Geologic events like volcanic eruptions, tectonic uplift, and erosion can disrupt the idealized rock cycle by altering rock formations or shifting materials between different stages. Interruptions are more common because Earth's dynamic processes constantly reshape and modify the environment, leading to incomplete or non-linear cycles. These interruptions reflect the complex and evolving nature of geological activity. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 9 provided in the appendix to the text) 7. How does the solar nebula theory account for the formation of our solar system, its features, and evolutionary history? Suggested Answer: According to The Solar Nebula Theory, stars form in massive, dense clouds of molecular hydrogen called giant molecular clouds. These clouds are gravitationally unstable, and matter coalesces into smaller, denser clumps inside. These clouds collapse and form stars. This can give birth to planets. So, the formation of planetary systems is thought to be a natural result of star formation. The process is thought to take at least 100 million years. The solar nebula theory explains the formation of our solar system by proposing that it originated from a rotating cloud of gas and dust. This nebula collapsed under gravity, forming a protostar (the Sun) at its center and a protoplanetary disk around it. Planets and other solar system bodies formed through accretion within this disk, leading to the diverse features and evolutionary history observed today. Chapter 2 Plate Tectonics: A Unifying Theory Chapter Outline 2.1 Introduction 2.2 Early Ideas About Continental Drift 2.3 What Is the Evidence for Continental Drift? 2.4 Features of the Seafloor 2.5 Earth’s Magnetic Field 2.6 Paleomagnetism and Polar Wandering 2.7 Magnetic Reversals and Seafloor Spreading 2.8 Plate Tectonics: A Unifying Theory GEO-INSIGHT 2.1: Plate Boundaries, Earthquakes, and Tsunami 2.9 The Three Types of Plate Boundaries 2.10 Hot Spots and Mantle Plumes 2.11 Plate Movement and Motion 2.12 The Driving Mechanism of Plate Tectonics 2.13 Plate Tectonics and the Distribution of Natural Resources 2.14 Plate Tectonics and the Distribution of Life Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Plate tectonics is the unifying theory of geology and has revolutionized geology. • The hypothesis of continental drift was based on considerable geologic, paleontologic, and climatologic evidence. • The hypothesis of seafloor spreading accounts for continental movement, and the idea that thermal convection cells provide a mechanism for plate movement. • The three types of plate boundaries are divergent, convergent, and transform. Along these boundaries, new plates are formed, consumed, or slide past one another. • Interaction along plate boundaries accounts for most of Earth’s earthquake and volcanic activity. • The rate of movement and motion of plates can be calculated in several ways. • Some type of convective heat system is involved in plate movement. • Plate movement affects the distribution of natural resources. • Plate movement affects the distribution of the world’s biota and has influenced evolution. Chapter Summary • The concept of continental movement is not new. The earliest maps showing the similarity between the east coast of South America and the west coast of Africa provided the first evidence that continents may once have been united and subsequently separated from each other. • Alfred Wegener is generally credited with developing the hypothesis of continental drift. He provided abundant geologic and paleontologic evidence to show that the continents were once united into one supercontinent which he named Pangaea. Unfortunately, Wegener could not explain how the continents moved, and most geologists ignored his ideas. • Various features of the continental margins and the seafloor are a reflection of plate movement. Continental margins are active or passive, depending on their relationship to plate boundaries. Oceanic trenches are long, steep-sided depressions on the seafloor near convergent plate boundaries where oceanic lithosphere is consumed by subduction. Submarine hydrothermal vents are found at or near spreading ridges and associated with divergent plate boundaries. • The hypothesis of continental drift was revised during the 1950s when paleomagnetic studies of rocks indicated the presence of multiple magnetic north poles instead of just one as there is today. This paradox was resolved by moving so that the paleomagnetic data became consistent with a single magnetic north pole. When this was done, the rock sequences, glacial deposits and striations, and fossil distributions aligned with the reconstructed paleogeography. • Seafloor spreading was confirmed by the discovery of magnetic anomaliesin the oceanic crust that were both parallel to and symmetric around the ocean ridges, indicating that new oceanic crust must have formed as the seafloor was spreading. The pattern of oceanic magnetic anomalies matched the pattern of magnetic reversals already known from continental lava flows and showed that Earth’s magnetic field has reversed itself numerous times during the past. • Radiometric dating reveals that the oldest oceanic crust is less than 180 million years old, whereas the oldest continental crust is approximately 4 billion years old. Fossil evidence and the thickness of sediments overlying the oceanic crust further support and confirm that ocean basins are recent geologic features. • Plate tectonic theory became widely accepted by the 1970s because the evidence overwhelmingly supports it and because it provides geologists with a powerful theory for explaining such phenomena as volcanism, earthquake activity, mountain building, global climatic changes, the distribution of the world’s biota, and the distribution of mineral resources. • Geologists recognize three types of plate boundaries: divergent boundaries, where plates move away from each other; convergent boundaries, where two plates collide; and transform boundaries, where two plates slide past each other. • Ancient plate boundaries can be recognized by their associated rock assemblages and geologic structures. For divergent boundaries, these may include rift valleys with thick sedimentary sequences and numerous dikes and sills. For convergent boundaries, ophiolites and andesitic rocks are two characteristic features. Transform plate boundaries generally do not leave any characteristic or diagnostic features in the geologic record. • The average rate of movement and relative motion of the plates can be calculated in several ways. The results of these different methods all agree and indicate that the plates move at different average velocities. • The absolute motion of plates can be determined by the movement of plates over mantle plumes. A mantle plume is an apparently stationary column of magma that rises to the surface from deep within the mantle and forms either a subsurface mushroom-shaped plume head, or erupts at the surface as a volcano. • Although a comprehensive theory of plate movement has yet to be developed, geologists think that some type of convective system is involved in plate movementA close relationship exists between the formation of petroleum, as well as some mineral deposits, and plate boundaries. Furthermore, the formation and distribution of many natural resources are related to plate movements. • The relationship between plate tectonic processes and the evolution of life is complex. The distribution of plants and animals is not random, but rather is controlled mostly by climate and geographic barriers, which, in turn, are influenced, to a great extent, by the movement of plates. Enrichment Topics Topic 1. Seeing Tectonic Plate Movement in Action. Global Positioning System (GPS) receivers are used to determine precise geodetic position measurements each day to chronicle plate movements. Horizontal movement vectors, which are the result of plate tectonic motions, are shown on the map, and motions for various locations can be graphed. http://sideshow.jpl.nasa.gov/mbh/series.html Topic 2. Is Plate Tectonics Inevitable? Plate tectonics may be a necessary condition for life and so the existence of plate tectonics on other earth-like planets is important for determining whether life may exist on those planets. Using the article “Inevitability of Plate Tectonics on Super-Earths” in The Astrophysical Journal have the students discuss why plate tectonics may be necessary for life to exist on a planet and whether how likely these large planets are to have plate tectonics. How can astronomers test whether a large planet is tectonically active and is home to living things? http://www.iop.org/EJ/abstract/1538-4357/670/1/L45/ Common Misconceptions Misconception 1: The crust moves on top of the mantle. Fact: This is a simplified picture of plate tectonics. In reality, the lithosphere, which includes both the crust and the solid uppermost mantle, moves about on the underlying asthenosphere, the part of the mantle exhibiting plastic behavior. Misconception 2: Earth is molten, except for its crust. Fact: Only small pockets of magma are molten, the rest of Earth is solid. Some, like the asthenosphere, is solid but it can flow plastically. Lecture Suggestions 1. Use animations to teach plate tectonics. Technology aids in the understanding of plate motions with these fantastic animations from the University of California, Santa Barbara. Global Tectonics topics include Mesozoic Subduction, Pangaea, Himalayan Collision, Seafloor Spreading, South Atlantic Spreading and Seafloor Spreading and Magnetic Reversals. Regional Plate Tectonics and Geologic Histories topics include Pacific Hemisphere Plate, 80 Ma to Present; N.E. Pacific and W. North American Plate History, 38 Ma to Present; and Plate Tectonic History of Southern California, 20 Ma to Present: http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html . More plate tectonics animations are found at the United States Geological Survey website: http://www.nature.nps.gov/Geology/usgsnps/animate/pltecan.html and at this University of California Berkeley site http://www.ucmp.berkeley.edu/geology/anim1.html 2. Relative rates of motion between tectonic plates are a difficult concept to grasp for many beginning geology students. The following is an illustration in which members of the class are designated as specific plates and plate margins that move with a set of tape measures. The setting is the western margin of North America 40 Ma, involving the Pacific, Farallon, and North American plates, a spreading ridge, and a subduction zone. Five students are designated as follows: Student 1 = Pacific plate Student 2 = West side of spreading ridge; reels out Pacific plate with tape measure Student 3 = East side of spreading ridge; reels out Farallon plate with tape measure Student 4 = Farallon plate Student 5 = North American plate and subduction zone; reels in Farallon plate Given: Rate of Pacific Plate with respect to North America plate = zero (therefore, students 1 and 5 are stationary in the illustration). Both students 2 and 3 reel out tape at a rate of 1 m/10 My (1m = 500km). Set-up: Two roll-up tape measures are used with a piece of bright electrical tape attached at each 1 inch interval. Student 1 stands on one side of the room. Students 2, 3, and 4 start approximately 3 meters from student 1. Student 5 stands across the room, approximately 8 meters from student 1. Students 2 and 3 move together throughout the demonstration and reel out tape at the same rate. Student 5 pulls in tape reeled out by student 3. Student 4 travels along with the tape reeled out by student 3. The following table is drawn on the blackboard: RATES OF MOTION Plate A relative to Plate B Rate in km/My Pacific plate to North America plate; Given as zero North America plate to ridge (50) Pacific plate to ridge (50) Farallon plate to ridge (50) Pacific plate to Farallon plate (100) Farallon plate to North America plate (100) The illustration is set-up and run for each set of plates in the table. The difference in rates between each pair of students is easily ascertained. 3. Why was the concept of seafloor spreading necessary for continental drift to be accepted? How could scientists ignore the overwhelming evidence that the continents could move over the face of the earth? 4. Use this idea to explain mid ocean ridge spreading. Many students in introductory geology generally understand that new crust is created at the mid oceanic ridge (MOR) by separation of plates, but some of the subtleties can escape them. For example, the bilateral symmetry of the paleomagnetic reversal pattern, or the migration of the ridge axis can be confusing. A demonstration using students can help clear up the situation. • Depending on the class size, all or part of the class may be used. Classrooms that have a central aisle are ideal. The volunteers, about 20 to 30 students, gather in the central aisle. They are referred to as the magma in the chamber underlying the central ridge axis. They are told to shuffle slowly to the front of the class in pairs, and for each pair to separate, one going left and the other to the right upon reaching the front of the room. When they reach the front of the room, they are to hold their arms up if the instructor's arms are up, or leave them down if the instructor's arms are down. • In this way, the plates grow at the front of the room, as the students diverge from each other at the ridge axis and are subsequently replaced by other students emerging from the magma chamber. • Hands up are normal polarity rocks and hands down are reverse polarity rocks. The bilateral symmetry of the paleomagnetic pattern and progression of rock age from oldest (first to come out) to youngest (last to come out) should now be obvious to most students. Having the students take a small step toward the audience for each minute that they are part of the new crust will generate the subsidence that is expressed as ridge topography. By varying the rate at which the students walk and separate, various paleomagnetic reversal pattern widths and ridge topographies (East Pacific Rise vs. Mid Atlantic Ridge) can be generated. 5. Note that the direction of plate movement at any given point along a spreading ridge or subduction zone must be perpendicular to that spreading ridge or subduction zone. 6. Stress the differences between continental and oceanic crust and between the lithosphere and the asthenosphere. Note especially the rigid behavior, lower density, and brittle, highly fractured nature of the continental crust. 7. A pot of boiling soup and its surface crust is a useful analogy for describing the process of convection cell motion. Consider This 1. Why is plate tectonics given the status of theory, while continental drift has attained only the status of hypothesis? Answer: Plate tectonics is considered a theory because it is a comprehensive, well-supported framework explaining the movement of Earth's lithospheric plates and their role in geological processes. Continental drift, initially a hypothesis proposed by Alfred Wegener, lacked sufficient evidence and mechanisms to explain how continents moved. Plate tectonics built upon and expanded this idea, integrating extensive evidence and providing a robust model. 2. Since plate movements have been directly measured, is plate tectonics a theory or a fact? Why or why not? Answer: Plate tectonics is a theory because it provides a comprehensive explanation of how and why plates move, integrating various observations and measurements. While the movement of plates has been directly measured, the term "theory" reflects its broad, unifying framework that interprets these measurements within the context of Earth's geological processes. Thus, it represents an overarching model rather than a simple fact. 3. Compare and contrast continental drift and the plate tectonic theory. What does plate tectonics have that continental drift does not? Answer: Continental drift, proposed by Wegener, suggested that continents moved across the Earth's surface but lacked a mechanism for this movement. Plate tectonics builds on this idea by providing a detailed mechanism, explaining that Earth's lithosphere is divided into moving plates driven by mantle convection. Unlike continental drift, plate tectonics integrates evidence from seismology, geology, and geophysics to form a comprehensive model of Earth's dynamic processes. 4. What is the origin of the term “transform” in transform fault? Answer: The term “transform” in transform fault originates from the fault's role in "transforming" or shifting the motion between adjacent tectonic plates horizontally, without creating or destroying crust. Unlike divergent or convergent boundaries, where plates move apart or together, transform faults accommodate lateral movements, effectively translating motion across the fault line. 5. Why are transform faults associated with spreading ridges at approximately right angles to the ridge? Why don't transform faults intersect subduction zones as well? Answer: Transform faults are associated with spreading ridges at right angles because they accommodate horizontal displacement between diverging plates along mid-ocean ridges. They connect segments of ridge systems, allowing for the lateral movement of crust. Transform faults typically do not intersect subduction zones because these zones involve vertical motions (plates sinking into the mantle), and transform faults primarily handle horizontal movements. 6. Why can spreading ridges never be directly connected to subduction zones, but instead, require the linking of the two by a transform fault? Answer: Spreading ridges and subduction zones cannot be directly connected because they involve different types of plate motions: divergent at ridges and convergent at subduction zones. Transform faults link these regions by accommodating horizontal motion between segments, thus allowing for the continuity of plate movements and preventing direct intersection of divergent and convergent boundaries. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 9. Historical Perspective http://pubs.usgs.gov/gip/dynamic/historical.html The United States Geological Survey provides an historical explanation of the development of plate tectonics theory. 10. The PLATES Project http://www.ig.utexas.edu/research/projects/plates/index.htm The Institute for Geophysics at the University of Texas the PLATES project provides a resource for plate tectonics media, publications and teaching resources. 11. This Dynamic Earth http://www.mnh.si.edu/earth/ Four topics are covered in this website by the Smithsonian National Museum of Natural History including Plate Tectonics and Volcanoes. 12. Mantle plumes.org http://www.mantleplumes.org/ This blog discusses the origin of “hotspot” volcanism and is frequented by some of the top names in the field. 13. Northern California Earthquake Data Center (NCEDC) http://quake.geo.berkeley.edu/ The NCEDC provides updates on earthquakes in northern California, including recent epicenters. 14. GPS Time Series http://sideshow.jpl.nasa.gov/mbh/series.html Global Positioning System (GPS) receivers are used to determine precise geodetic position measurements each day to chronicle plate movements. Videos 1. Colliding Continents. National Geographic DVD (2010, 50 mins.) Why do continents collide and what is the effects of those collisions? 2. Drain the Ocean: See What Lies Beneath Our Seas. National Geographic DVD (2010, 90 mins.) What would we see if we could remove the water from the oceans? This uses CGI animation and is based on the latest scientific research. 3. How the Earth Was Made. DVD (2009, 450 mins.) This 13-part series uses spectacular locations to study geological phenomena around the world. 4. Plate Tectonics. Insight Media DVD (2004, 15 mins.) Look at the development of plate tectonics theory as an example of the process of scientific inquiry. 5. World in Motion: Plate Tectonics. Insight Media DVD (2003, 27 mins.) What is the supporting evidence for plate tectonics? 6. Plate Tectonics. Insight Media DVD (2006, 25 mins.) Look at the evolution of the scientific understanding of plate tectonics as an example of the process of scientific inquiry. 7. Making the Pieces Fit: Continental Drift Theory. Insight Media DVD (2003, 27 mins.) Learn about the study of deep earthquakes and their impact on plate tectonics theory. 8. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #5: The Birth of a Theory. The development of continental drift, seafloor spreading, and plate tectonics theory. • #6: Plate Dynamics The movement and interaction of tectonic plates and the geological phenomena they account for. 9. Planet Earth. Annenberg Media http://www.learner.org/resources/series49.html, (1986, 1 hour, free video) • #1: The Living Machine: The Theory of Plate Tectonics. Plate tectonics revealed at geological sites such as Kilauea volcano and the Atlantic seafloor. • #5: Gifts from the Earth. Earth’s Natural Resources. Plate tectonics and how it has revolutionized the way geologists search for natural resources. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 2.3 Why is the best fit along the continental slope and not along the current coastline? Answer: As the supercontinents (both Pangaea and Gondwana) broke apart, the rifting created downfaulting; normal-faulted grabens adjacent to the current continental blocks. These grabens underlie part of the continental shelf and create the edge for this continental slope – the “tear” line of the divergent break up. (See Chapter 10 for more.) ❯❯ Critical Thinking Question Figure 2.16 How does the age of the oceanic crust confirm the seafloor spreading theory? Answer: The age of the continents – Billions of Years! The age of ocean crust – Hundreds of Millions! Today’s ocean basins have their geologic origin back to the time of the beginning of the Pangaean breakup. This theory dates back to the 1960s. Earthquakes, volcanoes, and mountain ranges tell us about the interaction of plate boundaries (so that’s where those boundaries are). The event in human history that confirmed “sea floor spreading” occurred as the Glomar Challenger’s drilling across the Atlantic continued to show the results – decrease in the age of the sediment and paleomagnetic reversals. The trend continued and was “mirrored” across the Mid-Atlantic Ridge. What a good time to be alive! Today, scientific evidence continues to pore in: GPS monitors continue to prove plate movement direction and speed. ❯❯ Critical Thinking Question Figure 2.23 If the movement along the San Andreas fault, which separates the Pacific plate from the North American plate, averages 5.5 cm per year, how long will it take before Los Angeles is opposite San Francisco? Answer: As Lucy Jones of the Cal Berkeley Seismology Lab stated after the Northridge quake, “In about 10 million years, LA will be a suburb of San Francisco.” To determine how long it will take for Los Angeles to move opposite San Francisco along the San Andreas fault, we need to know the current distance between the two cities. Suppose this distance is (d) cm. Given that the fault movement averages 5.5 cm per year, the time (T) required for Los Angeles to be directly opposite San Francisco can be calculated using: T = d5.5 years Without the exact distance (d), we can't calculate a specific time, but this formula will provide the answer once (d) is known. ❯❯ Critical Thinking Question Figure 2.30 Why is the mammalian fauna of Australia so different from elsewhere? Answer: Unique among the continents with diverse continental ecosystems, it is isolated in the middle of it tectonic plate with no “land bridge” potentials, and has been this way since before placental mammals evolved. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 8 provided in the appendix to the text) 10. Creative Thinking Visual Question: Using the ages (the numbers represent ages in millions of years) for each of the Hawaiian Islands, as well as the scale given in the figure below, calculate the average rate of movement per year for the Pacific plate since each island formed (Figure 1). Is the average rate of movement the same for each island? Would you expect it to be? Explain why it may not be and why there are different ages for some of the islands. Suggested Answer: Each of the Hawaiian Islands is generally older than the next when one moves up the island chain from southeast (the Big Island) to northwest (Kure). Because the Big Island is the only island with active volcanos, it is considered to be the hot spot from which the other islands were formed. If one uses the ages of each of the Hawaiian Islands, and divides by the distance from the Big Island of Hawaii, one can approximate the speed of movement of each island from the Big Island over time. To calculate the average rate of movement per year for the Pacific plate, divide the distance between each island and the hotspot by the age of each island in millions of years. The average rate is not the same for each island because the rate of plate movement can vary over time due to factors like mantle plume activity and changes in tectonic forces. The different ages of the islands reflect the varying times at which each island was formed as the plate moved over the hotspot. Student may follow these steps to answer this question: • Using the scale on the map, find the distance from the middle of Hawaii to spots on each island matching the age listed on the map. Answer: To find the distance from the middle of Hawaii to spots on each island matching the age listed on the map, use the map's scale to measure the distance from the central point of Hawaii to the indicated age locations on each island. Convert the measured distances using the scale to determine the actual distances in kilometers or miles. This method allows you to quantify the distance from the hotspot to different volcanic features corresponding to their ages. • Fill the information in a Data Worksheet similar to that listed below. Answer: To fill out a Data Worksheet, follow these steps: 1. Identify the key parameters such as location, age, and distance from a reference point (e.g., the middle of Hawaii). 2. Measure distances using the map scale for each location. 3. Record measurements in the worksheet, including distances and corresponding ages. 4. Double-check entries for accuracy and consistency. Ensure the data is organized clearly, with columns for the island name, age, distance, and any additional notes. • Next, calculate the rate at which the Pacific Plate moved since the formation of Molokai by dividing the distance by the ages indicated. Fill the value in on their own data table. Answer: To calculate the rate at which the Pacific Plate moved since the formation of Molokai, follow these steps: 1. Measure the distance from Molokai to the spot corresponding to its age. 2. Divide this distance by the age of the spot (in millions of years) to find the rate. 3. Fill in the calculated rate in the data table. 4. Ensure the rate is in units such as centimeters per year (cm/yr) by converting the distance and time appropriately. • Determine the rate of movement since the formation of each island. Answer: To determine the rate of movement since the formation of each island, follow these steps: 1. Measure the distance from the reference point (e.g., the hotspot) to the formation location of each island. 2. Divide the distance by the age of each island (in millions of years) to calculate the rate of movement. 3. Convert the rate to units like centimeters per year if needed. 4. Record the rate in your data table for each island. • After finding the rates of movement above, average the numbers to find the average rate of the Pacific Plate. To find the average rate of the Pacific Plate movement: 1. Sum the rates of movement calculated for each island. 2. Divide the total by the number of islands to get the average rate. 3. Ensure units are consistent (e.g., centimeters per year). 4. Record the average rate in your data table. Sample Data Table
Age of Islands Distance from Big Island Rate of Movement
(millions of years) (kilometers) (km/million years)
Nihau 4.9 450 0.0109
5.1
Oahu 3.7 475 0.0078
2.6
1.9
Molakai 1.8 225 0.0080
1.3
1.3
1
Maui 0.8 150 0.0053
0.43
0.38
0.15
0.01
0.004
Average 0.0080
Additional Resources for this question: • http://www.soest.hawaii.edu/GG/ASK/hawaii_volcano_age.html • http://esa21.kennesaw.edu/activities/platespeed/plate_speed.pdf • http://www.st.nmfs.noaa.gov/Assets/Nemo/documents/lessons/Lesson_13/Lesson_13-Teacher%27s_Guide.pdf • http://pubs.usgs.gov/gip/dynamic/Hawaiian.html Solution Manual for The Changing Earth: Exploring Geology and Evolution James S. Monroe, Reed Wicander 9781285733418
