Environmental Geology, 9th Edition PDF

mon24085_fm_i-xvi.indd Page i 12/21/09 11:13:27 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles ninth edition Environmental...

mon24085_fm_i-xvi.indd Page i 12/21/09 11:13:27 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles ninth edition Environmental Geology Carla W. Montgomery Professor Emerita Northern Illinois University TM mon24085_fm_i-xvi.indd Page ii 12/21/09 11:13:30 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles TM ENVIRONMENTAL GEOLOGY, NINTH EDITION Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved. Previous editions © 2008, 2006, and 2003. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning. Some ancillaries, including electronic and print components, may not be available to customers outside the United States. This book is printed on acid-free paper. 1 2 3 4 5 6 7 8 9 0 WDQ/WDQ 1 0 9 8 7 6 5 4 3 2 1 0 ISBN 978–0–07–352408–5 MHID 0–07–352408–5 Vice President, Editor-in-Chief: Marty Lange Vice President, EDP: Kimberly Meriwether David Director of Development: Kristine Tibbetts Publisher: Ryan Blankenship Executive Editor: Margaret J. Kemp Senior Marketing Manager: Lisa Nicks Senior Project Manager: Vicki Krug Senior Production Supervisor: Sherry L. Kane Designer: Michelle D. Whitaker (USE) Cover Image: © Doug Sherman/Geofile Lead Photo Research Coordinator: Carrie K. Burger Photo Research: Jerry Marshall/pictureresearching.com Compositor: Aptara, Inc. Typeface: 10/12 Times Roman Printer: Worldcolor Photos not credited on page provided by author, Carla W. Montgomery. All credits appearing on page or at the end of the book are considered to be an extension of the copyright page. Library of Congress Cataloging-in-Publication Data Montgomery, Carla W., 1951- Environmental geology / Carla W. Montgomery.—9th ed. p. cm. Includes bibliographical references and index. ISBN 978–0–07–352408–5 — ISBN 0–07–352408–5 (hard copy : alk. paper) 1. Environmental geology—Textbooks. I. Title. QE38.M66 2011 550—dc22 2009041010 www.mhhe.com mon24085_fm_i-xvi.indd Page iii 12/21/09 11:13:32 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles In Dedication Environmental Geology is affectionately dedicated to the memory of Ed Jaffe, whose confidence in an unknown author made the first edition possible. –CWM– mon24085_fm_i-xvi.indd Page iv 12/21/09 11:13:32 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles Preface cannot, for instance, use a resource that is not there, or build a About the Course secure home or a safe dam on land that is fundamentally un- stable. Geology, then, is a logical place to start in developing an Environmental Geology Is Geology Applied understanding of many environmental issues. The principal to Living aim of this book is to present the reader with a broad overview The environmentt is the sum of all the features and conditions of environmental geology. Because geology does not exist in a surrounding an organism that may influence it. An individual’s vacuum, however, the text introduces related considerations physical environment encompasses rocks and soil, air and wa- from outside geology to clarify other ramifications of the sub- ter, such factors as light and temperature, and other organisms. jects discussed. Likewise, the present does not exist in isolation One’s social environment might include a network of family from the past and future; occasionally, the text looks both at and friends, a particular political system, and a set of social how the earth developed into its present condition and where customs that affect one’s behavior. matters seem to be moving for the future. It is hoped that this Geology is the study of the earth. Because the earth pro- knowledge will provide the reader with a useful foundation for vides the basic physical environment in which we live, all of discussing and evaluating specific environmental issues, as geology might in one sense be regarded as environmental geol- well as for developing ideas about how the problems should be ogy. However, the term environmental geology is usually re- solved. stricted to refer particularly to geology as it relates directly to human activities, and that is the focus of this book. Environ- mental geology is geology applied to living. We will examine Features Designed for the Student how geologic processes and hazards influence human activities (and sometimes the reverse), the geologic aspects of pollution This text is intended for an introductory-level college course. It and waste-disposal problems, and several other topics. does not assume any prior exposure to geology or college-level mathematics or science courses. The metric system is used Why Study Environmental Geology? throughout, except where other units are conventional within a discipline. (For the convenience of students not yet “fluent” in One reason for studying environmental geology might simply metric units, a conversion table is included on the inside back be curiosity about the way the earth works, about the how and cover, and in some cases, metric equivalents in English units why of natural phenomena. Another reason is that we are in- are included within the text.) creasingly faced with environmental problems to be solved and Each chapter opens with an introduction that sets the decisions to be made, and in many cases, an understanding of stage for the material to follow. In the course of the chapter, one or more geologic processes is essential to finding an ap- important terms and concepts are identified by boldface type, propriate solution. and these terms are collected as “Key Terms and Concepts” at Of course, many environmental problems cannot be fully the end of the chapter for quick review. The Glossary includes assessed and solved using geologic data alone. The problems both these boldface terms and the additional, italicized terms vary widely in size and in complexity. In a specific instance, that many chapters contain. Most chapters include actual case data from other branches of science (such as biology, chemistry, histories and specific real-world examples. Every chapter con- or ecology), as well as economics, politics, social priorities, and cludes with review questions and exercises, which allow stu- so on may have to be taken into account. Because a variety of dents to test their comprehension and apply their knowledge. considerations may influence the choice of a solution, there is The “Exploring Further” section includes items that might frequently disagreement about which solution is “best.” Our serve as ideas for projects or research papers building on text personal choices will often depend strongly on our beliefs about material. which considerations are most important. Each chapter includes one or more case studies relating to the chapter material. Some involve a situation, problem, About the Book or application that might be encountered in everyday life. Others offer additional case histories or relevant examples. An introductory text cannot explore all aspects of environmen- The tone is occasionally light, but the underlying issues are tal concerns. Here, the emphasis is on the physical constraints nonetheless real. (While some case studies were inspired by imposed on human activities by the geologic processes that actual events, and include specific factual information, all have shaped and are still shaping our natural environment. In a of the characters quoted, and their interactions, are wholly real sense, these are the most basic, inescapable constraints; we fictitious.) iv mon24085_fm_i-xvi.indd Page v 1/14/10 8:47:05 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles of such retreating of alpine glaciers for water supplies in New and Updated Content many areas. Chapter 10 This chapter, new to the last edition, has been Environmental geology is, by its very nature, a dynamic field in considerably expanded, reflecting ever-growing interest which new issues continue to arise and old ones to evolve. Every in global climate change. The relatively greater warming chapter has been updated with regard to data, examples, and of the polar regions, and its significance, is examined illustrations. more fully. New information from the IPCC 2009 report Geology is a visual subject, and photographs, satellite is incorporated. Additional effects of climate change, imagery, diagrams, and graphs all enhance students’ learning. observed and postulated, are described: changes in Accordingly, this edition includes more than two hundred new phytoplankton productivity, changing ocean chemistry illustrations, with revisions having been made to dozens more. and its effect on corals, changing patterns of rainfall and In addition each chapter now features one or two Case Studies drought such as may have contributed to the recent to present contemporary issues. devastating Australian fires. The role of oceans as Significant content additions and revisions to specific thermal reservoir is further examined. Discussion of chapters include: paleoclimates and the evidence for them has been Chapter 1 A new case study examines models of lunar expanded. A case study addresses the problem of how, origin to illustrate hypothesis-testing in science. in fact, the earth’s temperature is measured, and how Population statistics have been updated, with increased some of those measurements support the connection focus on China and India. between warming and GHG. Some proposed Chapter 2 The asbestos case study has been expanded to “geoengineering” solutions to moderate climate change include some of the complexities of the Libby, Montana, are noted. vermiculite mine. Chapter 11 New information includes data showing that Chapter 3 Discussion of evidence supporting plate-tectonic evaporation losses from reservoirs exceed human water theory has been expanded, and a case study added to consumption worldwide, and evidence that use of illustrate how this theory supplanted the previous model desalinated water may cause deficiency disease in crops of mountain-building. if not in people. Case studies of the High Plains Aquifer Chapter 4 Discussions of fault types, of moment magnitude, System and the Aral Sea are updated. and of tsunami monitoring have been expanded. New Chapter 12 Impact of expansion of biofuel crops on case studies describe applications of short-term soil-conservation efforts are noted. A case study has earthquake early-warning systems, and studies related to been added to explore forensic geology as it involves the San Andreas Fault Observatory at Depth (SAFOD). soils and sediments. Chapter 5 Information has been added on the Mammoth Chapter 13 Data and graphs on mineral consumption, Lakes tree kills and the hazards of magmatic CO2, as well reserves, recycling, etc., have been fully updated. as on new evidence of links between earthquakes and Discussion of global mineral demand now includes volcanic activity. The status of activity at Kilauea and specific focus on the impact of China’s development. A Mount St. Helens has been updated. A new case study case study examines cell-phone e-cycling from a examines the threats posed by the reawakening of mineral-resource perspective. Redoubt volcano. Chapter 14 As with minerals, tables and graphs of fossil- Chapter 6 Updated case studies examine more broadly the fuel consumption and reserves have been updated. problem of characterizing flood frequency, and that of Expanded analysis of factors affecting possible oil controlling flooding on the Mississippi River system via exploration in ANWR now includes information on the levees. time factor in oil-field development. New/additional Chapter 7 Discussion of tides has been improved and information on mountaintop-removal coal mining, expanded. The case study involving the vulnerability of hazards of ash impoundments, and usefulness of coastal regions to hurricanes now addresses Hurricane coal-to-liquid technology has been included. Ike as well as Katrina, and illustrates the role of the Chapter 15 The Chernobyl case study has been updated, as Galveston seawall. have statistics on U.S. and global nuclear reactors Chapter 8 Landslides in the Pacific Northwest in the winter operating and under construction. Analysis of energy loss of 2008–2009 are now discussed. Coverage of landslide in generation of electricity has been expanded. New monitoring and prediction is expanded to illustrate issues include mineral-resource availability as a potential relationships of slide hazard to precipitation history. constraint on expanded use of photovoltaics, and the Chapter 9 Historic and modern photo pairs illustrate effect that widespread cultivation of biofuel crops can dramatic changes in several alpine glaciers. The case have on food supplies, land use, and carbon sinks. study considering glaciers as a water source has been Chapter 16 Data on municipal waste generation and expanded to explore more specifically the implications nuclear-waste handling in various parts of the world Preface v mon24085_fm_i-xvi.indd Page vi 12/21/09 11:13:34 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles have been updated, as has discussion of Superfund. The realities. The section on surface processes concludes with a problem of toxic elements in e-cycling is highlighted. chapter on climate, which connects or affects a number of the The case study examining “life cycle” comparison of surface processes described earlier in Section III. simple objects to assess environmental impact has been A subject of increasing current concern is the availability expanded. of resources. A series of five chapters deals with water re- Chapter 17 Mercury pollution is more fully examined. A sources, soil, minerals, and energy, the rates at which they are new case study on DDT highlights the environmental being consumed, probable amounts remaining, and projections persistence of bioaccumulative pesticides. New data on of future availability and use. In the case of energy resources, water quality in wells are presented. we consider both those sources extensively used in the past and Chapter 18 Data on emissions of EPA’s criteria air pollutants new sources that may or may not successfully replace them in have been updated, as have acid-rain maps. Expanded the future. discussions include the role of aerosols in weather, and Increasing population and increasing resource consump- carbon-sequestration strategies and experiments; new tion lead to an increasing volume of waste to be disposed of; information on residual lead in soils along highways has thoughtless or inappropriate waste disposal, in turn, commonly been added to the discussion of lead pollution. creates increasing pollution. Three chapters examine the inter- Chapter 19 “Cap-and-trade” as a strategy for reducing related problems of air and water pollution and the strategies pollution is now discussed. Discussion of seabed mining available for the disposal of various kinds of wastes. The intro- rights and the EEZ is expanded to include new legal duction to this section presents some related concepts from the developments and effects of global warming. field of geomedicine, linking geochemistry and health. Chapter 20 Three Gorges Dam is now a major case study, The final two chapters deal with a more diverse assort- with more information on hazards and concerns associated ment of subjects. Environmental problems spawn laws intended with the project, and problems already experienced. to solve them; chapter 19 looks briefly at a sampling of laws, policies, and international agreements related to geologic mat- At chapter ends, the old “For Further Thought” questions have ters discussed earlier in the book, and some of the problems been expanded and modified under the revised heading “Ex- with such laws and accords. Chapter 20 examines geologic con- ploring Further” to include a number of activities in which stu- straints on construction schemes and the broader issue of trying dents can engage, some involving online data, and some to determine the optimum use(s) for particular parcels of land— quantitative analysis. For example, they may be directed to ex- matters that become more pressing as population growth pushes amine real-time stream-gaging or landslide-monitoring data, or more people to live in marginal places. information on current or recent earthquake activity; they can Relative to the length of time we have been on earth, hu- manipulate historic climate data from NASA to examine trends mans have had a disproportionate impact on this planet. by region or time period; they may calculate how big a wind Appendix A explores the concept of geologic time and its mea- farm or photovoltaic array would be required to replace a con- surement and looks at the rates of geologic and other processes ventional power plant; they can even learn how to reduce sul- by way of putting human activities in temporal perspective. Ap- fate pollution by buying SO2 allowances. pendix B provides short reference keys to aid in rock and min- eral identification, and the inside back cover includes units of Organization measurement and conversion factors. Of course, the complex interrelationships among geologic The book starts with some background information: a brief processes and features mean that any subdivision into chapter- outline of earth’s development to the present, and a look at one sized pieces is somewhat arbitrary, and different instructors major reason why environmental problems today are so may prefer different sequences or groupings (streams and pressing—the large and rapidly growing human population. ground water together, for example). An effort has been made This is followed by a short discussion of the basic materials of to design chapters so that they can be resequenced in such ways geology—rocks and minerals—and some of their physical without great difficulty. properties, which introduces a number of basic terms and con- cepts that are used in later chapters. The next several chapters treat individual processes in de- Supplements tail. Some of these are large-scale processes, which may involve motions and forces in the earth hundreds of kilometers below Supplements for this edition include: Instructor’s Manual, Pre- the surface, and may lead to dramatic, often catastrophic events sentation Center, PowerPoint Lecture Outlines, and Student like earthquakes and volcanic eruptions. Other processes—such Quizzing. The “NetNotes” previously included at the end of as the flow of rivers and glaciers or the blowing of the wind— each chapter have been expanded and moved to the website. occur only near the earth’s surface, altering the landscape and They continue to highlight a modest collection of Internet sites occasionally causing their own special problems. In some cases, that provide additional information and/or images relevant to geologic processes can be modified, deliberately or acciden- the chapter content. These should prove useful to both students tally; in others, human activities must be adjusted to natural and instructors. An effort has been made to concentrate on sites vi Preface mon24085_fm_i-xvi.indd Page vii 12/21/09 11:13:34 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles with material at an appropriate level for the book’s intended Thomas B. Boving, Ernest H. Carlson, Elizabeth Catlos, Dennis audience and also on sites likely to be relatively stable in the DeMets, Hailiang Dong, Alexander Gates, Chad Heinzel, very fluid world of the Internet (government agencies, educa- Edward Kohut, Richard McGehee, Marguerite Moloney, Lee tional institutions, or professional-association sites). The end- Slater, and Dan Vaughn, and additional comments by Nathan of-chapter “Suggested Readings/References” have likewise Yee. Like its predecessors, this ninth edition has also been been updated and moved to the website, and the appendix on strengthed through the careful reading and thoughtful sugges- maps and satellite imagery included in previous editions has tions by reviewers: Christine Aide, Southeast Missouri State been moved there also. University; James Bartholomew, University of South Carolina; Thomas Boving, University of Rhode Island; Jim Constanto- poulos, Eastern New Mexico University; Mark Groszos, Acknowledgments Valdosta State University; Duke Ophori, Montclair State University; Bianca Pedersen, University of Wisconsin–Eau A great many people have contributed to the development of Claire; John Rockaway, Northern Kentucky University; Kevin one or another edition of this book. Portions of the manuscript Svitana, Otterbein College; and Clifford H. Thurber, University of the first edition were read by Colin Booth, Lynn A. Brant, of Wisconsin–Madison. Arthur H. Brownlow, Ira A. Furlong, David Huntley, John The input of all of the foregoing individuals, and of many F. Looney, Jr., Robert A. Matthews, and George H. Shaw, and the other users who have informally offered additional advice, has entire book was reviewed by Richard A. Marston and Donald substantially improved the text, and their help is most grate- J. Thompson. The second edition was enhanced through sug- fully acknowledged. If, as one reviewer commented, the text gestions from Robert B. Furlong, Jeffrey J. Gryta, David Gust, “just keeps getting better,” a large share of the credit certainly Robert D. Hall, Stephen B. Harper, William N. Mode, Martin belongs to the reviewers. Any remaining shortcomings are, of Reiter, and Laura L. Sanders; the third, with the assistance of course, my own responsibility. Susan M. Cashman, Robert B. Furlong, Frank Hanna, William M. Dalecheck, C. Edwards, I. Hopkins, and J. McGregor N. Mode, Paul Nelson, Laura L. Sanders, and Michael A. Velbel; at the USGS Photo Library in Denver provided invaluable as- the fourth, through the input of reviewers Herbert Adams, sistance with the photo research over the years. The encourage- Randall Scott Babcock, Pascal de Caprariis, James Cotter, Dru ment of a number of my colleagues—particularly Colin Booth, Germanoski, Thomas E. Hendrix, Gordon Love, Steven Lund, Ron C. Flemal, Donald M. Davidson, Jr., R. Kaufmann, and Michael McKinney, Barbara Ruff, Paul Schroeder, Ali Tabidian, Eugene C. Perry, Jr.—was a special help during the develop- Clifford Thurber, and John Vitek. The fifth edition was im- ment of the first edition. The ongoing support and interest of proved thanks to reviews by Kevin Cole, Gilbert N. Hanson, fellow author, deanly colleague, and ecologist Jerrold H. Zar John F. Hildenbrand, Ann E. Homes, Alvin S. Konigsberg, has been immensely helpful. Thanks are also due to the several Barbara L. Ruff, Vernon P. Scott, Jim Stimson, Michael thousand environmental geology students I have taught, many Whitsett, and Doreen Zaback; the sixth, by reviews from Ray of whom in the early years suggested that I write a text, and Beiersdorfer, Ellin Beltz, William B. N. Berry, Paul Bierman, whose classes collectively have provided a testing ground for W. B. Clapham, Jr., Ralph K. Davis, Brian E. Lock, Gregory many aspects of the presentations herein. Hancock, Syed E. Hasan, Scott W. Keyes, Jason W. Kelsey, My family has been supportive of this undertaking from John F. Looney Jr., Christine Massey, Steve Mattox, William the inception of the first edition. A very special vote of appre- N. Mode, William A. Newman, Clair R. Ossian, David L. Ozsvath, ciation goes to my husband Warren—ever-patient sounding Alfred H. Pekarek, Paul H. Reitan, and Don Rimstidt. Improve- board, occasional photographer and field assistant—in whose ments in the seventh edition were inspired by reviewers Thomas life this book has so often loomed so large. J. Algaeo, Ernest H. Carlson, Douglas Crowe, Richard A. Flory, Last, but assuredly not least, I express my deep gratitude Hari P. Garbharran, Daniel Horns, Ernst H. Kastning, Abraham to the entire McGraw-Hill book team for their enthusiasm, pro- Lerman, Mark Lord, Lee Ann Munk, June A. Oberdorfer, Assad fessionalism, and just plain hard work, without which success- I. Panah, James S. Reichard, Frederick J. Rich, Jennifer Rivers ful completion of each subsequent edition of this book would Coombs, Richard Sleezer, and Michael S. Smith, and the eighth have been impossible. edition benefited from suggestions by Richard Aurisano, Carla W. Montgomery Preface vii mon24085_fm_i-xvi.indd Page viii 1/14/10 8:47:42 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles Contents Preface iv S E C T I O N I Foundations C H A P T E R 1 C H A P T E R 2 An Overview of Our Rocks and Minerals— Planetary Environment 3 A First Look 23 Earth in Space and Time 4 Atoms, Elements, Isotopes, Ions, and The Early Solar System 4 Compounds 24 The Planets 4 Atomic Structure 24 Earth, Then and Now 5 Elements and Isotopes 24 Life on Earth 8 Ions 24 The Periodic Table 25 Geology, Past and Present 9 Compounds 25 The Geologic Perspective 9 Geology and the Scientific Method 10 Minerals—General 26 The Motivation to Find Answers 10 Minerals Defined 26 Wheels Within Wheels: Earth Cycles and Systems 11 Identifying Characteristics of Minerals 26 Other Physical Properties of Minerals 28 Nature and Rate of Population Growth 13 Growth Rates: Causes and Consequences 14 Types of Minerals 29 Growth Rate and Doubling Time 15 Silicates 30 Nonsilicates 31 Impacts of the Human Population 16 Farmland and Food Supply 16 Rocks 33 Case Study 2 Asbestos—A Tangled Topic 34 Population and Nonfood Resources 17 Uneven Distribution of People and Resources 18 Igneous Rocks 35 Disruption of Natural Systems 18 Sediments and Sedimentary Rocks 37 Case Study 1 Earth’s Moon 20 Metamorphic Rocks 39 S U M M A R Y 21 The Rock Cycle 39 K E Y T E R M S A N D C O N C E P T S 21 SUMMARY 42 EXERCISES 22 KEY TERMS AND CONCEPTS 42 EXERCISES 42 viii mon24085_fm_i-xvi.indd Page ix 1/14/10 8:48:10 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles S E C T I O N II Internal Processes C H A P T E R 3 Earthquake-Related Hazards and Their Reduction 73 Ground Motion 73 Plate Tectonics 44 Ground Failure 73 Tsunamis and Coastal Effects 80 Plate Tectonics—Underlying Concepts 46 Case Study 4.1 Megathrust Makes Mega-Disaster 81 Stress and Strain in Geologic Materials 46 Fire 83 Lithosphere and Asthenosphere 48 Locating Plate Boundaries 48 Earthquake Prediction and Forecasting 84 Seismic Gaps 84 Plate Tectonics—Accumulating Evidence 50 Earthquake Precursors and Prediction 84 The Topography of the Sea Floor 50 Current Status of Earthquake Prediction 84 Magnetism in Rocks—General 50 The Earthquake Cycle and Forecasting 85 Paleomagnetism and Seafloor Spreading 51 Earthquake Early Warnings? 86 Age of the Ocean Floor 52 Public Response to Earthquake Hazards 86 Polar-Wander Curves 52 Case Study 4.2 Understanding Faults Better—Parkfield and Types of Plate Boundaries 54 SAFOD 87 Divergent Plate Boundaries 55 Earthquake Control? 88 Convergent Plate Boundaries 56 Future Earthquakes in North America? 89 Transform Boundaries 58 Areas of Widely Recognized Risk 89 How Far, How Fast, How Long, How Come? 59 Other Potential Problem Areas 90 Past Motions, Present Velocities 59 SU M M A RY 91 KE Y TE RMS AND CONCE P TS 92 Why Do Plates Move? 61 E XE RCISES 92 Plate Tectonics and the Rock Cycle 61 Case Study 3 New Theories for Old—Geosynclines and Plate Tectonics 62 C H A P T E R 5 SUMMARY 63 KEY TERMS AND CONCEPTS 64 Volcanoes 93 EXERCISES 64 Magma Sources and Types 94 C H A P T E R 4 Styles and Locations of Volcanic Activity Continental Fissure Eruptions 96 96 Earthquakes 65 Individual Volcanoes—Locations 97 Shield Volcanoes 97 Earthquakes—Terms and Principles 67 Cinder Cones 98 Basic Terms 67 Composite Volcanoes 98 Earthquake Locations 69 Hazards Related to Volcanoes 99 Seismic Waves and Earthquake Severity 70 Lava 99 Seismic Waves 70 Pyroclastics 102 Locating the Epicenter 71 Case Study 5.1 Living with Lava on Hawaii 103 Magnitude and Intensity 72 Lahars 105 Contents ix mon24085_fm_i-xvi.indd Page x 1/14/10 11:53:56 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles Pyroclastic Flows—Nuées Ardentes 106 Response to Eruption Predictions 114 Toxic Gases 108 More on Volcanic Hazards in the United States 115 Steam Explosions 110 Cascade Range 115 Landslides and Collapse 110 Alaska and The Aleutians 115 Secondary Effects: Climate and Atmospheric Chemistry 110 Long Valley and Yellowstone Calderas 116 Case Study 5.2 Redoubt Volcano, Alaska 117 Issues in Predicting Volcanic Eruptions 111 S U M M A R Y 121 Classification of Volcanoes by Activity 111 K E Y T E R M S A N D C O N C E P T S 121 The Volcanic Explosivity Index 112 E X E R C I S E S 12 2 Volcanic Eruption Precursors 112 S E C T I O N III Surface Processes C H A P T E R 6 C H A P T E R 7 Streams and Flooding 124 Coastal Zones and The Hydrologic Cycle 125 Processes 150 Streams and Their Features 125 Nature of the Coastline 151 Streams—General 125 Waves and Tides 151 Sediment Transport 126 Sediment Transport and Deposition 153 Velocity, Gradient, and Base Level 127 Storms and Coastal Dynamics 153 Velocity and Sediment Sorting and Deposition 128 Emergent and Submergent Coastlines 155 Channel and Floodplain Evolution 130 Causes of Long-Term Sea-Level Change 155 Flooding 131 Signs of Changing Relative Sea Level 156 Factors Governing Flood Severity 131 Present and Future Sea-Level Trends 158 Flood Characteristics 133 Coastal Erosion and “Stabilization” 159 Stream Hydrographs 133 Beach Erosion, Protection, and Restoration 160 Flood-Frequency Curves 135 Cliff Erosion 161 Case Study 6.1 How Big Is the One Hundred-Year Flood? 137 Especially Difficult Coastal Environments 163 Consequences of Development in Floodplains 139 Barrier Islands 163 Strategies for Reducing Flood Hazards 140 Estuaries 165 Restrictive Zoning and “Floodproofing” 140 Case Study 7 Hurricanes and Coastal Vulnerability 166 Retention Ponds, Diversion Channels 141 Channelization 141 Costs of Construction—and Reconstruction— in High-Energy Environments 168 Levees 142 Recognition of Coastal Hazards 168 Flood-Control Dams and Reservoirs 142 S U M M A R Y 17 0 Case Study 6.2 Life on the Mississippi: A History of Levees 144 K E Y T E R M S A N D C O N C E P T S 17 0 Flood Warnings? 146 E X E R C I S E S 17 0 S U M M A R Y 14 8 K E Y T E R M S A N D C O N C E P T S 14 9 E X E R C I S E S 14 9 x Contents mon24085_fm_i-xvi.indd Page xi 12/21/09 11:13:38 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles C H A P T E R 8 Glacial Erosion and Deposition 199 Ice Ages and Their Possible Causes 201 Case Study 9 Vanishing Glaciers, Vanishing Water Supply 204 Mass Movements 171 Wind and Its Geologic Impacts 206 Factors Influencing Slope Stability 172 Wind Erosion 207 Effects of Slope and Materials 172 Wind Deposition 209 Effects of Fluid 173 Dune Migration 209 Effects of Vegetation 175 Loess 210 Earthquakes 176 Deserts and Desertification 210 Quick Clays 176 Causes of Natural Deserts 211 Types of Mass Wasting 177 Desertification 213 Falls 177 S U M M A R Y 215 K E Y T E R M S A N D C O N C E P T S 215 Slumps and Slides 177 E X E R C I S E S 215 Flows and Avalanches 178 Consequences of Mass Movements Impact of Human Activities 179 179 C H A P T E R 10 A Compounding of Problems: the Venezuelan Coast 182 Case Study 8 Vaiont Dam 184 Climate—Past, Possible Preventive Measures 184 Present, and Future 216 Slope Stabilization 186 Major Controls on Global Climate; The Recognizing the Hazards 187 Greenhouse Effect 217 Landslide Warnings? 191 Climate and Ice Revisited 218 S U M M A R Y 19 4 The Hidden Ice: Permafrost 219 K E Y T E R M S A N D C O N C E P T S 19 4 E X E R C I S E S 19 4 Oceans and Climate 219 The Thermohaline Circulation 221 C H A P T E R 9 El Niño 222 Other Aspects of Global Change 224 Ice and Glaciers, Wind and Evidence of Climates Past 227 Deserts 195 Case Study 10 Taking Earth’s Temperature 228 Whither for the Future? Climate Feedbacks, Glaciers and Glacial Features 196 Predictive Uncertainty 229 Glacier Formation 196 SUMMARY 232 Types of Glaciers 197 KEY TE RMS AND CONCE P TS 232 E XE RCISES 232 Movement and Change of Glaciers 197 Contents xi mon24085_fm_i-xvi.indd Page xii 1/14/10 8:48:42 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles S E C T I O N IV Resources Resources, People, and Standards of Living 235 SUMMARY 267 KEY TERMS AND CONCEPTS 267 Projection of Resource Supply and Demand 237 EXERCISES 267 C H A P T E R 11 C H A P T E R 12 Water as a Resource 239 Soil as a Resource 269 Fluid Storage and Mobility: Porosity and Soil Formation 270 Permeability 240 Soil-Forming Processes: Weathering 270 Subsurface Waters 241 Soil Profiles, Soil Horizons 273 Aquifer Geometry and Groundwater Flow 242 Confined and Unconfined Aquifers 242 Chemical and Physical Properties of Soils 274 Color, Texture, and Structure of Soils 274 Darcy’s Law and Groundwater Flow 243 Soil Classification 275 Other Factors in Water Availability 243 Consequences of Groundwater Withdrawal 244 Soils and Human Activities 277 Lateritic Soil 277 Lowering the Water Table 244 Wetland Soils 278 Compaction and Surface Subsidence 245 Soil Erosion 278 Saltwater Intrusion 247 Soil Erosion versus Soil Formation 280 Impacts of Urbanization on Groundwater Strategies for Reducing Erosion 283 Recharge 248 Irrigation and Soil Chemistry 285 Karst and Sinkholes 248 Case Study 12.1 Plantations in Paradise: Unintended Water Quality 251 Consequences 286 Measures of Water Quality 252 The Soil Resource—The Global View 287 Case Study 11 What’s in the Water? 252 Case Study 12.2 Suspects and Soils 289 Hard Water 253 SUMMARY 289 KEY TERMS AND CONCEPTS 290 Water Use, Water Supply 254 EXERCISES 290 General U.S. Water Use 254 Regional Variations in Water Use 257 Case Studies in Water Consumption 259 C H A P T E R 13 The Colorado River Basin 259 Mineral and Rock The High Plains (Ogallala) Aquifer System 261 The Aral Sea 262 Resources 291 Lake Chad 263 Ore Deposits 292 Extending the Water Supply 263 Types of Mineral Deposits 292 Conservation 263 Igneous Rocks and Magmatic Deposits 292 Interbasin Water Transfer 265 Hydrothermal Ores 294 Desalination 266 Sedimentary Deposits 296 xii Contents mon24085_fm_i-xvi.indd Page xiii 1/14/10 8:49:19 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles Other Low-Temperature Ore-Forming Processes 296 Environmental Impacts of Coal Use 334 Metamorphic Deposits 297 Gases 334 Mineral and Rock Resources—Examples 298 Ash 334 Metals 298 Coal-Mining Hazards and Environmental Impacts 334 Nonmetallic Minerals 298 Oil Shale 337 Rock Resources 299 Tar Sand 338 SUMMARY 339 Mineral Supply and Demand 299 KE Y TE RMS AND CONCE P TS 339 U.S. Mineral Production and Consumption 299 E XE RCISES 339 World Mineral Supply and Demand 301 Minerals for the Future: Some Options Considered 303 C H A P T E R 15 New Methods in Mineral Exploration 304 Marine Mineral Resources 306 Energy Resources— Conservation of Mineral Resources 308 Alternative Sources 341 Case Study 13 Mining Your Cell Phone? 309 Nuclear Power—Fission 343 Impacts of Mining-Related Activities 310 Fission—Basic Principles 343 S U M M A R Y 314 The Geology of Uranium Deposits 344 K E Y T E R M S A N D C O N C E P T S 314 E X E R C I S E S 314 Extending the Nuclear Fuel Supply 344 Concerns Related to Nuclear Reactor Safety 345 C H A P T E R 14 Case Study 15.1 Crisis at Chernobyl 346 Concerns Related to Fuel and Waste Handling 347 Risk Assessment, Risk Projection 348 Energy Resources— Nuclear Power—Fusion 350 Fossil Fuels 316 Solar Energy 351 Formation of Oil and Natural Gas Deposits 318 Solar Heating 352 Supply and Demand for Oil and Natural Gas 319 Solar Electricity 352 Oil 320 Geothermal Energy 355 Case Study 14.1 The Arctic National Wildlife Refuge— Traditional Geothermal Energy Uses 355 To Drill or Not to Drill? 322 Alternative Geothermal Sources 357 Natural Gas 324 Hydropower 358 Future Prospects 324 Limitations on Hydropower Development 359 Enhanced Oil Recovery 325 Alternate Natural Gas Sources 325 Energy from the Oceans 360 Conservation 327 Wind Energy 362 Oil Spills 327 Biofuels 363 Case Study 14.2 Energy Prices, Energy Uses 328 Waste-Derived Fuels 364 Coal 331 Alcohol Fuels 365 Formation of Coal Deposits 331 Case Study 15.2 Electricity’s Hidden Energy Costs 366 SUMMARY 368 Coal Reserves and Resources 332 KEY TERMS AND CONCEPTS 368 Limitations on Coal Use 332 EXERCISES 368 Contents xiii mon24085_fm_i-xvi.indd Page xiv 1/14/10 8:49:48 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles S E C T I O N V Waste Disposal, Pollution, and Health C H A P T E R 16 C H A P T E R 17 Waste Disposal 373 Water Pollution 406 Solid Wastes—General 374 General Principles 407 Municipal Waste Disposal 374 Geochemical Cycles 407 Sanitary Landfills 375 Residence Time 407 Incineration 378 Residence Time and Pollution 408 Ocean Dumping 378 Point and Nonpoint Pollution Sources 409 Reducing Solid-Waste Volume 380 Organic Matter 409 Handling (Nontoxic) Organic Matter 380 Biochemical Oxygen Demand 410 Recycling 381 Eutrophication 411 Other Options 382 Industrial Pollution 412 Toxic-Waste Disposal 385 Inorganic Pollutants—Metals 412 Case Study 16.1 Decisions, Decisions... 386 Case Study 17.1 Lessons from Minamata 416 Secure Landfills 387 Other Inorganic Pollutants 416 Deep-Well Disposal 387 Organic Compounds 418 Other Strategies 388 Problems of Control 419 Sewage Treatment 388 Thermal Pollution 420 Case Study 17.2 The Long Shadow of DDT 421 Septic Systems 388 Municipal Sewage Treatment 390 Agricultural Pollution 422 Case Study 16.2 The Ghost of Toxins Past: Superfund 392 Fertilizers and Organic Waste 422 Radioactive Wastes 392 Sediment Pollution 423 Radioactive Decay 393 Pesticides 424 Effects of Radiation 394 Reversing the Damage—Surface Water 425 Nature of Radioactive Wastes 395 Groundwater Pollution 427 Historical Suggestions: Space, Ice, and Plate Tectonics 396 The Surface—Ground Water Connection Explored 427 Seabed Disposal 397 Tracing Pollution’s Path 429 Bedrock Caverns for Liquid Waste 397 Reversing the Damage—Ground Water 431 Bedrock Disposal of Solid High-Level Wastes 398 Decontamination After Extraction 431 Waste Isolation Pilot Plant (WIPP): A Model? 399 In Situ Decontamination 431 The Long Road to Yucca Mountain 400 Damage Control by Containment—The Rocky Mountain No High-Level Radioactive Waste Disposal Yet 403 Arsenal 431 SUMMARY 404 New Technology Meets Problems from the Past: KEY TERMS AND CONCEPTS 404 California Gulch Superfund Site, Leadville, EXERCISES 404 Colorado 433 SUMMARY 434 KEY TERMS AND CONCEPTS 435 EXERCISES 435 xiv Contents mon24085_fm_i-xvi.indd Page xv 1/14/10 8:50:16 AM user-f465 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles C H A P T E R 18 Acid Rain 448 Case Study 18 Indoor Air Pollution? 450 Regional Variations in Rainfall Acidity and Impacts 452 Air Pollution 436 Air Pollution and Weather 453 Atmospheric Chemistry—Cycles and Residence Thermal Inversion 453 Times 437 Impact on Weather 455 Types and Sources of Air Pollution 438 Particulates 438 Toward Air-Pollution Control 455 Carbon Gases 440 Air-Quality Standards 455 Sulfur Gases 441 Control Methods 455 Nitrogen Gases and “Smog Ozone” 442 Automobile Emissions 456 The Ozone Layer and Chlorofluorocarbons (CFCs) 443 Carbon Sequestration 458 SUMMARY 459 Lead 446 KEY TERMS AND CONCEPTS 460 Other Pollutants 448 EXERCISES 460 S E C T I O N VI Other Related Topics Cost-Benefit Analysis 476 C H A P T E R 19 Problems of Quantification 476 Cost-Benefit Analysis and the Federal Government 476 Environmental Law Laws Relating to Geologic Hazards 477 and Policy 462 Construction Controls 477 Other Responses to Earthquake Hazards 478 Resource Law: Water 463 Flood Hazards, Flood Insurance 479 Surface-Water Law 463 Problems with Geologic-Hazard Mitigation Laws 480 Groundwater Law 464 The National Environmental Policy Act (1969) 480 Resource Law: Minerals and Fuels 464 Case Study 19 Impact Analysis and the Trans-Alaska Mineral Rights 464 Pipeline 483 Mine Reclamation 465 SUMMARY 484 KEY TERMS AND CONCEPTS 485 International Resource Disputes 465 EXERCISES 485 Law of the Sea and Exclusive Economic Zones 466 Antarctica 468 Pollution and Its Control 468 C H A P T E R 20 Water Pollution 468 Air Pollution 471 Land-Use Planning and Waste Disposal 471 Engineering Geology 486 The U.S. Environmental Protection Agency 472 Land-Use Planning—Why? 487 Defining Limits of Pollution 472 Land-Use Options 488 International Initiatives 473 Contents xv mon24085_fm_i-xvi.indd Page xvi 12/21/09 11:13:46 PM user-s-179 /Volumes/204/MHDQ173/mon24085%0/0073524085/mon24085_pagefiles The Federal Government and Land-Use Arranging Events in Order A-1 Planning 490 Correlation A-2 Maps as a Planning Tool 491 Uniformitarianism A-3 Case Study 20.1 How Green Is My—Golf Course? 496 How Old Is the Earth? A-4 Engineering Geology—Some Considerations 498 Early Efforts A-4 The Role of Testing and Scale Modeling 501 Nineteenth-Century Views A-5 Case Histories, Old and New 501 Radiometric Dating A-5 The Leaning Tower of Pisa 501 Radioactive Decay and Dating A-5 The Panama Canal 503 Choice of an Isotopic System A-5 Boston’s “Big Dig” 504 Radiometric and Relative Ages Combined A-6 Dams, Failures, and Consequences 505 The Geologic Time Scale A-6 The St. Francis Dam 505 Geologic Process Rates A-7 Other Examples and Construction Issues 506 SUMMARY A8 Case Study 20.2 Three Gorges Dam (It’s Not Only About KEY TERMS AND CONCEPTS A8 Safety) 508 S U M M A R Y 510 K E Y T E R M S A N D C O N C E P T S 510 Appendix B E X E R C I S E S 511 Mineral and Rock Identification B-1 Mineral Identification B-1 Appendix A A Note on Mineral Formulas B-1 Geologic Time, Geologic Process Rock Identification B-1 Rates A-1 Introduction A-1 G LO S S A RY G 1 Relative Dating A-1 I N D E X I 1 xvi Contents mon24085_ch01_001-022.indd Page 1 11/17/09 5:15:27 PM user-s180 /Volumes/204/MHDQ173/mon24085/0073524085/mon24085_pagefiles S E C T I O N I Foundations A sense of historical perspective helps us to appreciate current challenges and to anticipate future ones. Many modern environmental problems, such as acid rain and groundwater pollution, have come upon us very recently. Oth- ers, such as the hazards posed by earthquakes, volcanoes, and to address such issues as global climate change, sustainable development, and environmental protection. More recently, seventy countries committed to participate in the International Year of Planet Earth (IYPE), a joint initiative of UNESCO and the International Union of Geological Sciences that is aimed at landslides, have always been with us. sharing our growing knowledge of earth and geologic pro- Recognition that geologic processes affect all humanity cesses to help current and future generations live more safely on our shared planet is illustrated by growing international de- and sustainably. bate and cooperation on the issues. The 1990s were designated Chapter 1 briefly summarizes major stages in the earth’s the United Nations Decade for Natural Disaster Reduction development and allows us to begin to see where current and (though ironically, both the number of catastrophic events, future human activities fit in. It provides us with some informa- and their toll in dollars and lives, soared to all-time highs in that tion about the solar system to help the reader judge the degree period). Concerted efforts by developed nations have sharply to which other planets might provide solutions to such prob- curtailed destruction of our protective ozone layer. In 1992, lems as lack of resources and living space. It also introduces the more than 170 nations came together in Rio de Janeiro for the concept of cyclicity in natural processes, and points out that the United Nations Conference on Environment and Development, interrelationships among natural processes may be complex. Rocks can provide building materials, yield mineral and energy resources, make the soil on which we live and grow crops, offer us recreational opportunities, and even be objects of veneration. Rainbow Bridge, AZ, is sacred to several native cultures. mon24085_ch01_001-022.indd Page 2 11/17/09 5:15:35 PM user-s180 /Volumes/204/MHDQ173/mon24085/0073524085/mon24085_pagefiles The size and growth of earth’s human population bear It is difficult to talk for long about geology without dis- strongly on the ways and extent to which geology and people cussing rocks and minerals, the stuff of which the earth is made. interact, which is what environmental geology is all about. In Chapter 2 introduces these materials and some of their basic fact, many of our problems are as acute as they are simply properties. Specific physical and chemical properties of rocks because of the sheer number of people who now live on the and soils are important in considering such diverse topics as re- earth, either overall or in particular locations. This will be evi- source identification and recovery, waste disposal, assessment of dent in later discussions of resources, pollution, and waste volcanic or landslide hazards, weathering processes and soil for- disposal. mation, and others. 2 Section One Foundations mon24085_ch01_001-022.indd Page 3 12/1/09 10:27:53 AM user-s180 /Volumes/204/MHDQ173/mon24085/0073524085/mon24085_pagefiles C H A P T E R An Overview of Our Planetary Environment 1 A bout five five billion years ago, out of a swirling mass of gas and dust, evolved a system of varied planets hurtling around a nuclear-powered star—our solar system. One of these planets, study our planet in systematic ways, we have ha developed an ever- increasing understanding of the complex nature of the processes shaping, and the problems posed by, our geological environment. and one only, gave rise to complex life-forms. Over time, a tremen- Environmental geology explores the many and varied interac- dous diversity of life-forms and ecological systems developed, tions between humans and that geologic environment. while the planet, too, evolved and changed, its interior churning, As the human population grows, it becomes increasingly its landmasses shifting, its surface constantly being reshaped. difficult for that population to survive on the resources and land Within the last several million years, the diversity of life on earth remaining, to avoid those hazards that cannot be controlled, and has included humans, increasingly competing for space and sur- to refrain from making irreversible and undesirable changes in vival on the planet’s surface. With the control over one’s surround- environmental systems. The urgency of perfecting our under- ings made possible by the combination of intelligence and manual standing, not only of natural processes but also of our impact on dexterity, humans have found most of the land on the planet in- the planet, is becoming more and more apparent, and has moti- habitable; they have learned to use not only plant and animal re- vated increased international cooperation and dialogue on envi- sources, but minerals, fuels, and other geologic materials; in some ronmental issues. (However, while nations may readily agree on respects, humans have even learned to modify natural processes what the problematic issues are, agreement on solutions is often that inconvenience or threaten them. As we have learned how to much harder to achieve!) A 180-degree panorama of images taken by the Mars rover Spirit in 2008, in colors approximating what the human eye would see. Image by NASA/JPL/Cornell. 3 mon24085_ch01_001-022.indd Page 4 12/1/09 10:28:08 AM user-s180 /Volumes/204/MHDQ173/mon24085/0073524085/mon24085_pagefiles dense and hot from the crushing effects of its own gravity that Earth in Space and Time nuclear reactions were triggered inside it. Meanwhile, dust con- densed from the gases remaining in the flattened cloud disk ro- The Early Solar System tating around the young sun. The dust clumped into planets, the In recent decades, scientists have been able to construct an ever- formation of which was essentially complete over 4½ billion clearer picture of the origins of the solar system and, before years ago. that, of the universe itself. Most astronomers now accept some sort of “Big Bang” as the origin of today’s universe. Just before it occurred, all matter and energy would have been compressed The Planets into an enormously dense, hot volume a few millimeters (much The compositions of the planets formed depended largely on less than an inch) across. Then everything was flung violently how near they were to the hot sun (figure 1.2). The planets apart across an ever-larger volume of space. The time of the Big formed nearest to the sun contained mainly metallic iron and a Bang can be estimated in several ways. Perhaps the most direct few minerals with very high melting temperatures, with little is the back-calculation of the universe’s expansion to its appar- water or gas. Somewhat farther out, where temperatures were ent beginning. Other methods depend on astrophysical models lower, the developing planets incorporated much larger amounts of creation of the elements or the rate of evolution of different of lower-temperature minerals, including some that contain wa- types of stars. Most age estimates overlap in the range of 12 to ter locked within their crystal structures. (This later made it 14 billion years. possible for the earth to have liquid water at its surface.) Still Stars formed from the debris of the Big Bang, as locally farther from the sun, temperatures were so low that nearly all of high concentrations of mass were collected together by gravity, the materials in the original gas cloud condensed—even materi- and some became large and dense enough that energy-releasing als like methane and ammonia, which are gases at normal earth atomic reactions were set off deep within them. Stars are not surface temperatures and pressures. permanent objects. They are constantly losing energy and mass The result was a series of planets with a variety of compo- as they burn their nuclear fuel. The mass of material that ini- sitions, most quite different from that of earth. This is confirmed tially formed the star determines how rapidly the star burns; by observations and measurements of the planets. For example, some stars burned out billions of years ago, while others are the planetary densities listed in table 1.1 are consistent with a probably forming now from the original matter of the universe higher metal and rock content in the four planets closest to the mixed with the debris of older stars. sun and a much larger proportion of ice and gas in the planets Our sun and its system of circling planets, including the farther from the sun (see also figure 1.3). These differences should earth, are believed to have formed from a rotating cloud of gas be kept in mind when it is proposed that other planets could be and dust (small bits of rock and metal), some of the gas debris mined for needed minerals. Both the basic chemistry of these from older stars (figure 1.1). Most of the mass of the cloud co- other bodies and the kinds of ore-forming or other resource- alesced to form the sun, which became a star and began to forming processes that might occur on them would differ consid- “shine,” or release light energy, when its interior became so erably from those on earth, and may not have led to products we Disk of gas and dust spinning around the young sun Dust grains Dust grains clump into planetesimals Planetesimals collide and collect into planets Figure 1.1 Our solar system formed as dust condensed from the gaseous nebula, then clumped together to make planets. 4 Section One Foundations mon24085_ch01_001-022.indd Page 5 12/1/09 10:30:43 AM user-s180 /Volumes/204/MHDQ173/mon24085/0073524085/mon24085_pagefiles would find useful. (This is leaving aside any questions of the economics or technical practicability of such mining activities!) In addition, our principal current energy sources required living organisms to form, and so far, no such life-forms have been found on other planets or moons. Venus—close to Earth in space, simi- lar in size and density—shows marked differences: Its dense, Gaseous planets cloudy atmosphere is thick with carbon dioxide, producing plan- etary surface temperatures hot enough to melt lead through run- away greenhouse-effect heating (see chapter 10). Mars would likewise be inhospitable: It is very cold, and we could not breathe its atmosphere. Though its surface features indicate the presence of liquid water in its past, there is none now, and only small amounts of water ice have been found. There is not so much as a blade of grass for vegetation; the brief flurry of excitement over possible evidence of life on Mars referred only to fossil microor- ganisms, and more-intensive investigations suggested that the tiny structures in question likely are inorganic. Earth, Then and Now Rocky/metallic planets The earth has changed continuously since its formation, under- going some particularly profound changes in its early history. The early earth was very different from what it is today, lacking the modern oceans and atmosphere and having a much different surface from its present one, probably more closely resembling the barren, cratered surface of the moon. Like other planets, Earth was formed by accretion, as gravity collected together the solid bits that had condensed from the solar nebula. Some water may have been contributed by gravitational capture of icy comets, though recent analyses of modern comets do not suggest that this was a major water source. The planet was heated by the impact of the colliding dust particles and meteorites as they came together to form the earth, and by the energy release from decay of the small amounts of several naturally radioactive elements that the earth contains. These heat sources combined to raise the earth’s Figure 1.2 internal temperature enough that parts of it, perhaps eventually As this graph shows, the spacing of the planets’ orbits exhibits a most of it, melted, although it was probably never molten all at geometric regularity. Note that the distance scale is logarithmic— once. Dense materials, like metallic iron, would have tended to outer planets are much farther out, proportionately, and formed at sink toward the middle of the earth. As cooling progressed, much colder temperatures. Table 1.1 Some Basic Data on the Planets Mean Distance from Mean Equatorial Diameter, Density* Planet Sun (millions of km) Temperature (°C) Relative to Earth (g/cu. cm) Mercury 58 167 0.38 5.4 Venus 108 464 0.95 5.2 Predominantly rocky/metal Earth 150