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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: Wiley Self-Teaching Guides
- Sprache: Englisch
The only popular study guide available on environmental science This new Wiley Self-Teaching Guide introduces learners to all the basics of environmental science, from air pollution to the water cycle, covering both natural systems and human impacts on the environment. Using quick quizzes and self-tests to reinforce key concepts, Environmental Science walks students through this interdisciplinary topic with clarity and thoroughness. With 125 photographs and illustrations, this book is a unique and valuable resource for anyone interested in learning more about-and in preserving-our green home.
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Seitenzahl: 564
Veröffentlichungsjahr: 2015
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CONTENTS
Cover
Title
Copyright
Acknowledgments
A Note to the Reader
1: Our Unique Planet
Objectives
The Environment and Environmental Science
Hot Topics in Environmental Science
Welcome to Our World
What Makes Earth Unique?
Earth, Inside and Out
Internal Forces
2: The Interactive Earth
Objectives
Systems
Earth as a Closed System
Cycles and Reservoirs
Fluxes
Box Models
Sources and Sinks
Residence Time and Turnover Time
Feedbacks
Biogeochemical Cycles
3: The Hydrosphere and the Atmosphere
Objectives
The Hydrosphere
The Ocean
Oceanic Circulation
Tides, Waves, and Shorelines
The Atmosphere
Atmospheric Circulation
Weather
Climate
4: The Biosphere: Life on Earth
Objectives
Life on Earth
Basic Biologic Processes: An Overview
Evolution and Species
Ecology
Energy in Ecosystems
Biomass and Biologic Productivity
5: Earth’s Major Ecosystems
Objectives
Biomes
An Introduction to Terrestrial Biomes
The Major Terrestrial Biomes
An Introduction to Aquatic Biomes
The Major Aquatic Biomes: Freshwater and Transitional
The Major Aquatic Biomes: Marine
6: Habitat and Biodiversity
Objectives
Ecologic Niche and Species Interactions
Conservation and Keystone Species
Biologic Diversity
Why Is Biodiversity Important?
Threats to Biodiversity
7: People, Population, and Resources
Objectives
Population Dynamics
Human Population Growth
The Demographic Transition
Human Impacts on the Environment
Basic Concepts in Resource Use and Management
8: Living Resources I: Forests, Wildlife, and Fisheries
Objectives
Forest Resources
Logging, Forest Management, and Agroforestry
The Causes of Deforestation
Wildlife and Wilderness
Fisheries and Aquaculture
9: Living Resources II: Soils and Agriculture
Objectives
Soils and Soil Nutrients
Traditional and Modern Agriculture
The Green Revolution and the Environmental Impacts of Modern Agriculture
Erosion and Loss of Agricultural Soil
Sustainable Agriculture and the World Food Supply
10: Mineral Resources
Objectives
Mineral Resources and Modern Society
Finding and Exploiting Mineral Resources
How Mineral Deposits Are Formed
Environmental Impacts: The Mining Process
Impacts on Land, Air, Water, and the Biosphere
11: Energy Resources
Objectives
Energy Basics
Fossil Fuels
Fossil Fuels and the Environment
Unconventional Hydrocarbons and New Hydrocarbon Technologies
Alternatives to Fossil Fuels
Alternative Energy: Solar, Wind, Hydrogen, and Biomass
Alternative Energy: Gravitational and Geothermal Energy
Nuclear Energy and the Environment
12: Water Resources
Objectives
Surface Water Processes
Flooding and Channel Modifications
Groundwater Processes
Fresh Water as a Resource
Water Law and Water Management
13: Water Pollution and Soil Pollution
Objectives
Drinking Water
The Contaminants in Environmental Reservoirs
Environmental Health and Toxins
Surface Water Pollution
Sediment Pollution
Groundwater Contamination
The Remediation of Contaminated Sites
14: Air Pollution
Objectives
Air Pollution: Sources and Processes
Cities and Pollution
Indoor Air Pollution
Acid Deposition
15: Cities and Waste Management
Objectives
Urbanization
The Physical Impacts of Urbanization
The Socioeconomic Impacts of Urbanization
Sustainable Cities
Solid Waste: Sources and Types
Waste Disposal
Dealing with Sewage
16: Global Change
Objectives
Global Change
Studying Past Environmental Change
Glaciations
The Natural and Anthropogenic Factors That Drive Climatic Change
Global Warming and Its Possible Consequences
Modeling the Global Climate System
Stratospheric Ozone
The Ozone Hole
International Policy Aspects of Global Change
Spaceship Earth
Appendix 1: Units and Conversions
About SI Units
Prefixes for Very Large and Very Small Numbers
Commonly Used Units of Measure
Appendix 2: Some Great Environmental Science Web Sites
Appendix 3: Soil Classifications
Cross-Merchandising Advertisements
Index
End User License Agreement
List of Figures
Chapter 1: Our Unique Planet
Figure 1.1.
Figure 1.2.
Figure 1.3.
Figure 1.4.
Figure 1.5.
Figure 1.6.
Chapter 2: The Interactive Earth
Figure 2.1.
Figure 2.2.
Figure 2.3.
Figure 2.4.
Figure 2.5.
Figure 2.6.
Figure 2.7A.
Figure 2.7B.
Chapter 3: The Hydrosphere and the Atmosphere
Figure 3.1.
Figure 3.2A.
Figure 3.2B.
Figure 3.3.
Figure 3.4.
Figure 3.5.
Figure 3.6.
Figure 3.7.
Figure 3.8.
Figure 3.9.
Chapter 4: The Biosphere: Life on Earth
Figure 4.1.
Figure 4.2.
Figure 4.3.
Figure 4.4.
Figure 4.5.
Chapter 5: Earth’s Major Ecosystems
Figure 5.1.
Figure 5.2.
Figure 5.3.
Figure 5.4.
Figure 5.5.
Figure 5.6.
Chapter 6: Habitat and Biodiversity
Figure 6.1.
Figure 6.2.
Figure 6.3.
Figure 6.4.
Figure 6.5.
Figure 6.6.
Chapter 7: People, Population, and Resources
Figure 7.1.
Figure 7.2.
Figure 7.3.
Figure 7.4.
Figure 7.5.
Figure 7.6.
Figure 7.7.
Chapter 8: Living Resources I: Forests, Wildlife, and Fisheries
Figure 8.1.
Figure 8.2.
Figure 8.3.
Figure 8.4.
Figure 8.5.
Figure 8.6.
Chapter 9: Living Resources II: Soils and Agriculture
Figure 9.1.
Figure 9.2.
Figure 9.3.
Figure 9.4.
Figure 9.5.
Figure 9.6.
Figure 9.7.
Figure 9.8.
Chapter 10: Mineral Resources
Figure 10.1.
Figure 10.2.
Figure 10.3.
Figure 10.4.
Chapter 11: Energy Resources
Figure 11.1.
Figure 11.2.
Figure 11.3.
Figure 11.4.
Figure 11.5.
Figure 11.6.
Figure 11.7.
Figure 11.8.
Chapter 12: Water Resources
Figure 12.1.
Figure 12.2.
Figure 12.3.
Figure 12.4.
Figure 12.5.
Figure 12.6.
Chapter 13: Water Pollution and Soil Pollution
Figure 13.1.
Figure 13.2.
Figure 13.3.
Figure 13.4.
Figure 13.5.
Figure 13.6.
Figure 13.7.
Chapter 14: Air Pollution
Figure 14.1.
Figure 14.2.
Figure 14.3.
Figure 14.4.
Figure 14.5.
Chapter 15: Cities and Waste Management
Figure 15.1.
Figure 15.2.
Figure 15.3.
Figure 15.4.
Chapter 16: Global Change
Figure 16.1.
Figure 16.2.
Figure 16.3.
Figure 16.4.
Figure 16.5.
Figure 16.6.
Figure 16.7.
Figure 16.8.
Figure 16.9.
Figure 16.10.
Figure 16.11.
Figure 16.12.
Figure 16.13.
List of Tables
Chapter 3: The Hydrosphere and the Atmosphere
Table 3.1 Composition of Earth’s Atmosphere (in percent, by volume)
Chapter 9: Living Resources II: Soils and Agriculture
Table 9.1 Factors That Influence Weathering
Chapter 10: Mineral Resources
Table 10.1 Mineral Resources
Table 10.2 Resources and Reserves
Table 10.3 The Potential Environmental Impacts of Mining
Chapter 12: Water Resources
Table 12.1 The Porosity and Permeability of Some Earth Materials
Table 12.2 Countries Currently Designated as Water-Scarce
Table 12.3 Some Examples of Internationally Shared Rivers
Chapter 13: Water Pollution and Soil Pollution
Table 13.1 Common Soil and Water Pollutants
Chapter 14: Air Pollution
Table 14.1 Some Major Air Pollutants and Their Health Effects
Chapter 15: Cities and Waste Management
Table 15.1 Mega-Cities of the World: 2005 and 2015 Population (in millions)
Chapter 16: Global Change
Table 16.1 Some Important Greenhouse Gases, Common Sources, and Relative Contributions to the Enhanced (Anthropogenic) Greenhouse Effect
Guide
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Environmental Science
A Self-Teaching Guide
Barbara W. Murck
Copyright © 2005 by Barbara W. Murck. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada
Photo credits: page 2, NASA Earth Observatory; page 20, Mark Emery/U.S. Fish and Wildlife Service; page 59, Jacques Descloitres/NASA Earth Observatory; page 77, Florida Keys National Marine Sanctuary; pages 83 and 236, USGS; page 114, Gary Kramer/U.S. Fish and Wildlife Service; pages 126, 140, and 165, FAO Photo; page 191, David Nimick/USGS; page 208, OMVS, Senegal; page 228, UNEP, Peter Garside, Topham Picturepoint; page 261, Tehran Times; page 276, NASA Goddard Space Flight Center; page 323, NASA Manned Spacecraft Center.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permissions.
Limit of Liability/Disclaimer of Warranty: While the publisher and the author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor the author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
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Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. For more information about Wiley products, visit our web site at www.wiley.com.
Library of Congress Cataloging-in-Publication Data:
Murck, Barbara Winifred, date
Environmental science : a self-teaching guide / Barbara W. Murck.
p. cm.
Includes index.
ISBN-13 978-0-471-26988-5 (pbk.)
ISBN-10 0-471-26988-3 (pbk.)
1. Environmental sciences—Programmed instruction. I. Title.
GE105.M87 2005
333.72—dc22
2004020587
Acknowledgments
Many thanks to the ever-professional team at John Wiley & Sons, especially Jeff Golick and Eric Nelson for inviting me to add Environmental Science to the Wiley Self-Teaching Guide series, and Kimberly Monroe-Hill for steering the manuscript through the production process. As always, my deep thanks to Professor Brian Skinner, my coauthor on a number of Wiley projects, for his advice, his vast knowledge, and his sharing nature. And thanks to my family for their continued acceptance of the never-ending mess on the dining room table.
A Note to the Reader
The environment is all around us—the solid Earth, the air, and the water, supporting and sustaining people, plants, and wildlife. But the environment is more than this. It encompasses the parts of the Earth system and all the living organisms that inhabit it, as well as the endless variety of interactions between them. The environment isn’t really a thing as much as it is an active, complex, ever-changing relationship.
This book focuses primarily on the scientific aspects of the study of the environment. Environmental science is both an interdisciplinary science and an applied science; it draws its fundamental principles from a number of basic scientific disciplines, particularly biology, geology, chemistry, and physics. These and other scientific disciplines such as hydrology, climatology, oceanography, soil science, statistics, and meteorology are applied to the study of the environment, contributing to our understanding of this complex planet we inhabit.
The science of the environment is multifaceted. Because we are talking about a relationship rather than a thing, the study of the environment extends significantly beyond the realm of science. People are the de facto managers of this planet. We manage the Earth system—its impacts on human society and in turn human impacts on the natural environment—as best we can, through our laws, policies, writings, and other human systems. We draw from disciplines as diverse as philosophy and ethics, art and literature, economics, political science, sociology, management, geography, history, anthropology, and even psychology. Thus, although the scientific aspects of the environment are foremost in this book, you will find that social, political, economic, and philosophic aspects are necessarily interwoven throughout. The book begins with a focus on Earth as a planet and some of the important processes in the natural world that shape and influence our environment (chapters 1 through 6). Later chapters focus more on people and technology and their influences on environmental quality (chapters 7 through 16).
Each chapter in the book begins with a brief list of the main things you will be learning about. Here and there you will find some text set apart like this:
This icon indicates something intriguing to think about, or an activity or experiment you might want to try for yourself.
Throughout the book you will find questions and answers, as well as a Self-Test at the end of each chapter, to test your comprehension and retention of concepts and vocabulary.
You can read the chapters in any order you choose. However, each chapter assumes that you understand the vocabulary and concepts presented in the preceding chapters. The first six chapters, in particular, introduce many of the basic concepts that are applied in subsequent chapters. For example, chapter 12 “Water Resources,” chapter 13 “Water Pollution and Soil Pollution,” and chapter 14 “Air Pollution” all build upon basic concepts introduced in chapter 3 “The Hydrosphere and the Atmosphere.” Boldface vocabulary terms are generally introduced once, although they may be briefly redefined in succeeding chapters.
Since you have purchased this book, you probably fall into one of these categories:
You studied environmental science a number of years ago in college or university and want to refresh or update your understanding of the subject.
You are currently studying environmental science in high school, college, or university and want to supplement your understanding of the material covered in lectures and labs.
You have developed an interest in environmental science, perhaps through watching documentaries or news stories about topics such as global warming, ozone depletion, smog alerts, or the loss of biodiversity.
You are a professional in a field that has been affected by environmental change, such as the insurance industry, engineering, municipal management, or the health professions.
In any case, you bought this book because you want to enhance your understanding of the science of our environment. Whatever your background, I hope this book will meet your needs and that you will enjoy reading it. I hope it will help you to learn more about our environment and to become a more informed and active participant in the management of the human–environment relationship.
1Our Unique Planet
We speak for Earth.
—Carl Sagan
Objectives
In this chapter you will learn about:
the field of environmental science;
the features and characteristics that make Earth unique;
the geosphere, atmosphere, hydrosphere, biosphere, ecosphere, and technosphere; and
the materials and processes of the solid Earth.
The Environment and Environmental Science
Once upon a time, the term environment just meant “surroundings.” It was used in reference to the physical world separate from ourselves—rocks, soil, air, and water. People gradually came to realize that the organisms that inhabit the physical world—the enormous variety of plants, animals, and microorganisms on this planet, including humans—are an integral part of the environment. It doesn’t make sense to define environment without recognizing the fundamental importance of interactivity among organisms, and between organisms and their surroundings. Therefore, we can define environment to include all of the components, characteristics, and conditions in the natural world that influence organisms, as well as the interactions between and among organisms and the natural world. This definition encompasses the physical–chemical–geologic surroundings of an organism, as well as the other biologic inhabitants of the neighborhood. It implies that there is a range of possible interactions among the various components of the environment, both biotic (living) and abiotic (nonliving).
This satellite image shows North and South America as they would appear from space 35,000 km (22,000 mi) above Earth. The image is a combination of data from two satellites: NASA’s Terra satellite collected the land data, and NOAA’s GOES satellite collected the cloudcover data.
Our conceptual understanding of the environment continues to evolve, reflecting the emerging understanding that humans, too, are an integral part. We influence the physical world and other organisms; in turn, we are influenced by them. Therefore, more recent definitions of environment incorporate social, cultural, and economic factors in addition to the components of the natural, biophysical world. For example, human technology is affected by the natural environment through the availability or scarcity of natural resources. Technology, in turn, has profound and sometimes devastating impacts on the natural environment. Understanding the technosphere—the built, manufactured, industrialized, and domesticated aspects of the world—is fundamental to our understanding and successful management of the environment.
Environmental science, the focus of this book, is an interdisciplinary combination of basic sciences applied to the study of the environment. By one relatively early definition, environmental science includes “all of nature we perceive or can observe . . . a composite of Earth, Sun, sea, and atmosphere, their interactions, and the hazards they present” (from the U.S. Environmental Science Services Administration, 1968). Environmental science draws its fundamental principles from a number of basic scientific disciplines, particularly biology, geology, chemistry, and physics. These and other scientific disciplines, including hydrology, climatology, oceanography, soil science, statistics, and meteorology, are applied to the study of the environment and contribute to our understanding of this complex planet we inhabit.
Environmental science is a multifaceted discipline, but the study of the environment extends well beyond the realm of science. People are the de facto managers of this planet. We manage the environment—our impacts on the environment, as well as its impacts on human society—through our laws, policies, writings, and other human systems. We draw from disciplines as diverse as philosophy, literature, economics, political science, sociology, management, geography, history, anthropology, art, and even psychology. The application of these disciplines to the environment has given rise to such fields as environmental law, environmental economics, environmental management, and environmental ethics. Although these are not scientific disciplines, they are fundamental to our understanding of the environment.
How would you modify the definition of environment stated above so that it takes into consideration human technology and its interactions with the natural environment? ________________
Answer: One possible definition is that environment encompasses the natural physical, chemical, biologic, and geologic aspects and conditions that influence and are influenced by organisms, including humans; the interactions among them; and social, cultural, and economic factors that influence and are influenced by the natural world. Does this definition include everything that you think it should?
Why do you think it is important to be precise and thorough in defining the concept of environment? ________________
Answer: One reason is that the term environment is often used in a legal context, where the wording must be very precise. Another reason for being careful and thorough is that how we define environment reflects, in part, how we view ourselves in relation to other organisms and to the natural world. The impacts of technologic developments on the natural environment sometimes result in degradation of the social or cultural environment; these need to be included in our definition so that they will be taken into consideration when we undertake activities that may alter the natural environment.
Hot Topics in Environmental Science
If you were to take a poll in which you asked citizens of North America and Europe to name the most pressing environmental issues today, you would likely find significant regional variations. People in the northeastern United States and southern Canada might have concerns about the health of the Great Lakes. In the Northwest, people might have concerns about deforestation in old-growth forests. In the Midwest and dry Southwest, the availability of abundant water and the depletion of groundwater supplies might be of concern. People in Western Europe might be most worried about the effects of acid rain on forests and lakes. Some concerns would be common to all regions, including climatic change, the ozone hole, loss of biodiversity, health impacts of air pollution, toxic contaminants in natural waters, overpopulation, energy shortages, and municipal garbage. These are widespread or even global problems that are part of the legacy of industrialization. Throughout this book, we will be looking at the science that underlies these and other environmental problems.
What are the most pressing environmental issues facing your local neighborhood, city, or region? How do they differ from the environmental issues in other regions, and how are they similar? How do your local concerns differ from global environmental issues?
If you were to conduct the same poll in a less economically developed country, perhaps in South America, Asia, or Africa, the list of pressing environmental issues might be quite different. The environmental concerns of people in the developing world tend to be more local, more immediate, and relate more directly to daily survival. The list might include land degradation and its impact on food production; lack of clean water for drinking, washing, and cooking; and the lack of fuel wood and other energy sources for cooking. Today almost 2 billion of the world’s poorest people lack access to sanitation facilities and wastewater treatment. Approximately 1 billion people do not have access to clean water, and almost 1 billion people are chronically hungry. These problems threaten people’s survival; they are part of the legacy of poverty. Some of them are not strictly environmental problems—there are underlying political, social, and economic causes—but the impacts of environmental degradation on human health and well-being are immediate, local, and severe in the developing world.
Until fairly recently, most developing countries were not particularly interested in entering the international dialogue about dealing with problems like ozone depletion or global warming. Why? It’s partly an issue of responsibility and blame; some of our current global environmental problems were caused—or were at least initiated—by industrialization in wealthier nations. It’s also partly because people in developing countries are simply too busy dealing with the immediate problems of daily survival and with getting food, water, and other basic services to people in need. Now, however, it is widely recognized that regardless of the cause everyone in the world is potentially at risk from the impacts of environmental degradation. All nations and all people bear a common responsibility to deal with these problems.
A concept that has become familiar in international dialogues about global environmental issues is the idea of common but differentiated responsibility of nations. What do you think it means? ________________
Answer: Common but differentiated responsibility refers to the concept that all nations must bear responsibility for dealing with global environmental problems, but different nations have different capacities and resources with which to respond to these problems.
Welcome to Our World
Now that we have covered some basic terminology and concepts, let’s begin our study of the environment by taking a look at the planet itself. Earth is one of nine planets in our solar system—the Sun and the group of objects orbiting around it, which originated as a system approximately 4.6 billion years ago. The solar system also includes more than sixty moons, a vast number of asteroids, millions of comets, and innumerable floating fragments of rock and dust. The objects in our solar system move through space in smooth, regular orbits held in place by gravitational attraction. The planets, asteroids, and comets orbit the Sun, and the moons orbit the planets (Figure 1.1).
The planets can be separated into two groups on the basis of their characteristics and distances from the Sun. The innermost planets—Mercury, Venus, Earth, and Mars—are small, rocky, and relatively dense. These planets are similar in size and chemical composition. They are called terrestrial planets because they resemble Terra (“Earth” in Latin). With the exception of Pluto, the outer or jovian planets—Jupiter, Saturn, Uranus, and Neptune—are much larger than the terrestrial planets but much less dense, with very thick atmospheres of hydrogen, helium, and other gases. You can learn more about the solar system by reading Astronomy: A Self-Teaching Guide, by Dinah L. Moché ( John Wiley & Sons, 2004).
Figure 1.1.
The terrestrial planets have many things in common beyond their small sizes, rocky compositions, and positions close to the Sun. They have all been subjected to volcanic activity and intense meteorite impact cratering. They have all been hot and, indeed, partially molten at some time early in their histories. During this partially molten period, the terrestrial planets separated into layers of differing chemical composition: a relatively thin, low-density, rocky crust on the outside; a metallic, high-density core in the center; and a rocky mantle in between. This separation process happened to all of the terrestrial planets, including Earth. In the context of environmental science, the physical Earth—distinct from the organisms that inhabit it—is referred to as the geosphere. The term geosphere is used in reference to the planet and the whole physical environment—the atmosphere, the hydrosphere, and the solid Earth.
What are the four terrestrial planets, and why are they given this name? ________________
Answer: Mercury, Venus, Earth, and Mars. They are all similar to Earth (Terra).
What Makes Earth Unique?
In spite of the similarities among the terrestrial planets, the history and specific characteristics of Earth are different enough from those of the other terrestrial planets to make this planet habitable. If you look at a photograph of Earth taken from space, you immediately notice the blue-and-white atmosphere, an envelope of gases dominated by nitrogen, oxygen, argon, and water vapor, with traces of other gases. Other planets have atmospheres, but no other planet in the solar system has an atmosphere of this particular chemical composition.
The atmosphere contains clouds of condensed water vapor that form because water evaporates from the hydrosphere, another unique feature. The hydrosphere (“watery sphere”) consists of the oceans, lakes, and streams; underground water; and snow and ice. Planets farther from the Sun are too cold for liquid water to exist on their surfaces; planets closer to the Sun are so hot that any surface water evaporated long ago. Only Earth has just the right surface temperature to have liquid water, ice, and water vapor in its hydrosphere.
Another unique feature of Earth is the biosphere, the “living sphere.” The biosphere comprises innumerable living things, large and small, which belong to millions of different species, as well as recently dead plants and animals that have not yet completely decomposed. The ecosphere is the physical environment that permits or facilitates the existence of the biosphere. On Earth, the ecosphere extends from the deepest valleys and the bottom of the ocean to the tops of the highest mountains and well into the lower part of the atmosphere. Even the great polar ice sheets host a variety of life forms. Although many new planets have been discovered orbiting distant stars that seem similar to our own Sun, we don’t yet know of another planet that offers an ecosphere or hosts a biosphere.
The nature of Earth’s solid surface is also special; it is covered by an irregular blanket of loose debris called regolith (from the Greek rhegos, meaning “blanket”). Earth’s regolith forms as a result of weathering, the continuous chemical alteration and mechanical breakdown of surface materials through exposure to the atmosphere, hydrosphere, and biosphere. The weathered, broken-down materials are picked up by moving wind, water, and ice, carried downhill under the influence of gravity, and eventually deposited. Weathering and the transport of weathered materials together comprise the process of erosion, which is part of the global rock cycle (Figure 1.2). Soil, mud in river valleys, sand in the desert, rock fragments, and other unconsolidated debris are all part of the regolith. Some other planets and planetary bodies are blanketed by loose, fragmented material, but in those cases the fragmentation has been caused primarily by the endless pounding of meteorite impacts. Earth’s regolith is unique because it forms as a result of complex interactions of physical, chemical, and biologic processes, usually involving water. It is also unique because it teems with life; most plants and animals live on or in the regolith or in the hydrosphere.
Figure 1.2.
Why does Earth have an ecosphere, whereas all other known planets do not? ________________
Answer: A combination of just the right size and composition (especially the presence of water) and optimal distance from the Sun make the surface conditions on Earth perfectly suited for hosting life.
Earth, Inside and Out
Earth, like the other terrestrial planets, is composed primarily of rock, a naturally formed, solid, coherent aggregate. The basic building blocks of rocks are minerals—naturally occurring, inorganic elements or chemical compounds that have specific chemical compositions, orderly internal atomic structures, and characteristic physical properties. Geology is the scientific study of these and other Earth materials and processes. If you are interested in learning more about the science of the Earth, you can read Geology:A Self-Teaching Guide, by Barbara Murck (John Wiley & Sons, 2001).
Three basic families of rocks are recognized. They are:
sedimentary rocks
, which form as a result of the deposition, consolidation, and cementation of unconsolidated rock and mineral fragments (
sediment
) in low-temperature and low-pressure conditions near Earth’s surface;
igneous rocks
, which solidify from molten rock (
magma
or
lava
) on the surface (
volcanic rocks
) or deep underground (
plutonic rocks
); and
metamorphic rocks
, which are rocks that have been altered as a result of exposure to very high pressures and/or temperatures.
As everyone knows, rocks are quite durable. However, we live on a planetary surface that is extremely active and ever changing. Winds blow, waves break, streams flow, and glaciers grind away at the surface. These constant, restless energetic forces, driven partly by gravity and partly by solar energy, interact with surface materials, eventually breaking down rocks and minerals to form regolith. Geologic evidence shows that weathering and erosion have been operating throughout most of Earth history—well over 4 billion years. But if these forces are constantly at work, inevitably wearing down and washing away Earth’s surface materials, then why are there any mountains left standing? The answer is that other forces are acting on the surface from the inside. Internal forces constantly uplift the surface, creating great mountains and rugged topography that seem to defy the forces of weathering and erosion. Here is how it works.
The outermost, rocky part of Earth is the crust, as mentioned above. Continental crust (Figure 1.3) is relatively thick (average thickness 45 km, or 30 mi) and is made mostly of plutonic rocks called granite. Oceanic crust, which underlies the great ocean basins, is relatively thin (average thickness 8 km, or 5.4 mi) and is made mostly of volcanic rocks called basalt. Beneath the crust is the mantle, which is also made of plutonic igneous rocks, but they are different from the rocks of the continental crust. At the center of Earth is the core made of ironnickel metal. Together, the crust and the outermost part of the mantle make up the lithosphere, a thin, cold, brittle, rocky layer. The mantle below the lithosphere is very hot, so it is malleable, like putty, even though it is made of solid rock. The part of the mantle immediately beneath the lithosphere is called the asthenosphere; it is especially weak and squishy because it is close to the temperature at which rocks begin to melt.
The lithosphere is made of solid rock about 100 km (60 mi) thick, on average. In comparison to the size of the planet as a whole, the lithosphere is an exceedingly thin shell (Figure 1.3). It has about the same relative thickness as the glass shell of a lightbulb or the skin of an apple.
Figure 1.3.
If you were to do an experiment in which you placed a thin, cool, brittle shell (like the lithosphere) on top of hot, weak material that is rather squishy (like the asthenosphere), what do you think would happen? You might predict that the thin shell would break into pieces. In fact, that is precisely what has happened to the lithosphere—it has broken into a number of large fragments, or plates. Today there are six large plates, each extending for several thousands of kilometers, and a large number of smaller plates (Figure 1.4). Note that these are lithospheric plates, not crustal plates. The plates are made of the crust and the solid rock of the mantle just beneath. Some lithospheric plates, like the Pacific Plate, are capped mainly by oceanic crust; others, like the North American Plate, are capped mainly by continental crust.
You can experiment with plates and plate motion by carefully heating wax in a pan, then letting it cool until it forms a thin skin or crust. If you try this, be careful—molten wax is very hot. Be sure to wear eye protection, and use care in handling hot pans.
Figure 1.4.
Think again about the expected behavior of thin, brittle fragments floating on top of hot, squishy material. You might expect that movements in the underlying material would cause the brittle fragments to shift about. Again, that is exactly what happens to Earth’s lithospheric plates. When movements occur in the hot mantle, the lithospheric plates shift and interact with one another. If a plate happens to be capped by continental crust, the continent moves along with the rest of the plate. You may already be familiar with this process; it is called continental drift. The study of the movement and interactions of lithospheric plates is referred to as plate tectonics (from the Greek word tekton, meaning “carpenter” or “builder”).
What is the lithosphere? ________________
Answer: The outer 100 km (60 mi) of Earth; the crust and the upper part of the mantle.
Internal Forces
Lithospheric plates move and shift their positions in response to movements in the mantle beneath. As the plates move, they interact with one another mainly along their edges. Plate margins are where the most violent and intense types of geologic activity originate. Plates can interact in three basic ways: they can move away from each other (diverge); they can move toward each other (converge); or they can slide past each other. Consequently, there are three basic kinds of plate margins (Figure 1.5):
Divergent margins
are huge fractures in the lithosphere where plates move apart from one another, forming great rift valleys on continents and under the oceans. They are characterized by earthquakes caused by the splitting and frac turing of rocks, and by volcanic activity that occurs when melted rock from deep within the mantle wells up through the fractures.
Figure 1.5.
Convergent margins
occur where two plates move toward each other, slowly colliding. At ocean–ocean and ocean–continent convergent margins, a process called
subduction
occurs, in which oceanic crust is forced down into the mantle (
Figures 1.5B
and
1.6)
. The downgoing plate melts when it reaches a depth within Earth where the temperature is sufficiently high. Thus, convergent plate margins that involve oceanic crust are characterized by active volcanism. Other convergent plate margins—those that involve only continental crust—are characterized by the uplifting of great mountain chains like the Himalayas (
Figure 1.5C
). All convergent plate margins are marked by intense earthquakes.
Transcurrent
or
transform fault margins
are huge fractures in the lithosphere where two plates slide past each other, grinding along their edges and causing earthquakes as they go. A famous modern example is the San Andreas Fault in California, where the Pacific Plate is moving north–northwest relative to the North American Plate.
All of these types of plate interactions are occurring today, as they have occurred throughout most of Earth history. We don’t often notice plate motion because lithospheric plates move very slowly—usually between 1 and 10 cm (0.4 and 4 in) per year. But we feel the earthquakes and observe the volcanic activity along active plate margins. The scars and remnants of ancient plate interactions are also preserved in the rock record for us to study.
Figure 1.6.
What causes plate motion? Thermal movement in the mantle is at least partly responsible (see Figure 1.6). Movement in the mantle, in turn, is caused by the release of heat from inside the Earth. The temperature in Earth’s interior is high—about 5,000°C (more than 9,000°F) in the core. Some of this heat is left over from the planet’s origin, but some of it is generated by the constant decay of naturally occurring radioactive elements. This heat must be released; if it were not, Earth would eventually become so hot that its entire interior would melt.
Some of Earth’s internal heat makes its way slowly to the surface through conduction, in which heat energy is transferred from one atom to the next. However, conduction is a slow way to transfer heat. It is faster and more efficient for a packet of hot material to be physically transported to the surface. This is similar to what happens when a fluid boils on a stovetop, as in the wax experiment described earlier in this chapter. If you watch a fluid such as wax or spaghetti sauce as it boils, you will see that it turns over and over. Packets of hot material rise from the bottom of the pot to the top. As it reaches the surface, the hot fluid cools, then sinks back down to the bottom of the pot, where it is reheated. The continuous motion of material from bottom to top and down again is called a convection cell, and this type of heat transfer is called convection.
Even though Earth’s mantle is mostly solid rock, it is so hot that it releases heat by convection. Rock deep in the mantle heats up and expands, making it buoyant. As a result, the rock moves toward the surface very slowly in huge convection cells of solid rock. Near the surface, the hot rock moves along the surface while losing heat to the atmosphere, just like the spaghetti sauce. As the rock cools, it becomes denser (cool rock is denser, or heavier, than hot rock) and sinks back into the deeper parts of the mantle. This convection cycle provides an efficient way for Earth to get rid of some of its internal heat.
The movement of lithospheric plates, formation of new crustal material through volcanism and tectonic uplift, and recycling of plates back into the mantle is called the tectonic cycle. Convection, plate motion, and interactions along plate margins create some of the most distinctive geologic and topographic features of the Earth’s surface: deep oceanic trenches where lithospheric plates sink back into the mantle; midocean ridges and continental rift valleys where plates split apart; and high folded and crumpled mountain chains that form where continents collide. Plate tectonism is also responsible for generating earthquakes and volcanic eruptions, among other geologic processes that make the surface of Earth such a dynamic, active place.
So, we can now add plate tectonics to our list of unique features. Earth differs from all other known planets because of the unique relationship between its thin, brittle lithosphere and the hotter, weaker rocks that lie below in the asthenosphere. Plate tectonic activity has been an important process throughout much of Earth history. It is responsible for the uplifting of mountains, eruptions of volcanoes, intensities of earthquakes, movement of continents, and formation of deep ocean basins. It has even influenced the formation and chemistry of the atmosphere, the development of climatic zones, and the evolution of life, as you will learn in later chapters.
What is the cause of lithospheric plate motion? ________________
Answer: The release of heat through convection in the mantle.
Why do you think oceanic crust undergoes subduction but continental crust does not? ________________
Answer: Oceanic crust is much denser than continental crust; therefore, continental crust rides up and over a colliding plate, whereas the denser oceanic crust is forced down into the mantle.
So . . . what makes Earth unique? Let’s summarize:We know of no other planet where plate tectonics has played and continues to play such an important role in shaping both the land and the physical environment. We know of no other planet where water exists near the surface in solid, liquid, and gaseous forms. No other planet yet discovered offers an ecosphere or hosts a biosphere or would have been hospitable to the origin and evolution of life as we know it. There are billions upon billions of stars in the universe, so it is almost inevitable that there are billions of planets; surely a few of those planets must be Earthlike and therefore capable of supporting life. However, if life does exist on a planet somewhere out in space, we haven’t found it so far.
After reading this chapter, you should have a basic understanding of some of the factors that shape our relationship to the physical, chemical, biologic, and geologic world. In environmental science a lot of attention is paid to the interactions and interrelationships among the various spheres introduced in this chapter: the geosphere, atmosphere, and hydrosphere; the ecosphere; the biosphere; and the technosphere. We will revisit many of the topics and ideas introduced in this chapter in greater detail later in the book. In the meantime, you can test your knowledge and retention of this introductory material by trying out the Self-Test.
SELF-TEST
These questions are designed to help you assess how well you have learned the concepts presented in chapter 1. The answers are given at the end. If you get any of the questions wrong, be sure to troubleshoot by going back into that part of the chapter to find the correct answer.
Which one of the following is not a terrestrial planet?
Mars
Venus
Mercury
Neptune
The irregular blanket of loose debris that covers the surface of Earth is called the ________________.
lithosphere
regolith
asthenosphere
mantle
The
plates
in plate tectonics are made of fragments of ________________.
continents
oceanic crust
lithosphere
mantle
The weak layer of the mantle immediately underlying the lithosphere is called the ________________.
Earth has two fundamentally different types of crust: ________________ crust is made mainly of basaltic rocks, and ________________ crust is made mainly of granitic rocks.
Earth formed approximately 4.6 million years ago. (True or False)
The abiotic components of the environment are the living organisms that make up the biosphere. (True or False)
The term
technosphere
refers to the built, manufactured, industrialized, and domesticated parts of the world. (True or False)
Summarize the features that make Earth unique.
Briefly describe the processes of weathering and erosion.
What is convection, and how does it work inside the Earth?
What is the difference between the biosphere and the ecosphere?
What are the three main types of plate margins?
ANSWERS
d
b
c
asthenosphere
oceanic; continental
False
False
True
Presence of an ecosphere and biosphere; liquid water at the surface; surface temperature amenable to life; role of plate tectonics; characteristics of the regolith; composition of the atmosphere.
The process of weathering occurs when surface rocks and minerals disintegrate, either by chemical alteration or mechanical breakdown. Erosion happens when the weathered fragments are picked up by moving wind, water, or ice, carried downhill, and deposited.
Convection is a mechanism of heat transfer in which hot material is physically transported from a hot area to a cooler area. Inside the Earth, hot rock near the core becomes buoyant and rises toward the surface, where it cools. Through cooling, the rock becomes denser and eventually sinks back into the mantle, to be heated once again.
These terms are sometimes used interchangeably.
Ecosphere
refers specifically to an environment that is favorable to the existence of life.
Biosphere
refers to the actual living organisms—the life that is hosted by the ecosphere. Sometimes biosphere is used specifically to refer to Earth’s ecosphere.
The three main types of plate margins are:
divergent
convergent
transform or transcurrent fault
KEY WORDS
abiotic
asthenosphere
atmosphere
biosphere
biotic
conduction
continental crust
continental drift
convection
convergent margin
core
crust
divergent margin
ecosphere
environment
environmental science
erosion
geology
geosphere
hydrosphere
igneous rock
jovian planet
lava
lithosphere
magma
mantle
metamorphic rock
mineral
oceanic crust
plate
plate tectonics
plutonic rock
regolith
rock
rock cycle
sediment
sedimentary rock
solar system
subduction
technosphere
tectonic cycle
terrestrial planet
transcurrent or transform fault margin
volcanic rock
weathering
2The Interactive Earth
When we try to pick out anything by itself, we find it hitched to everything else in the universe.
—John Muir
Objectives
In this chapter you will learn about:
the storage and cycling of materials and energy within the Earth system;
interactions among Earth’s subsystems and cycles;
the balance in natural systems and how it can be affected by human activities; and
the transfer of life-supporting elements from one part of the Earth system to another.
Systems
In environmental science today, there is a strong emphasis on the study of Earth as a unified, interconnected system rather than as a collection of isolated parts. The concept of a system helps us break down large, complex problems into smaller pieces that are easier to study without losing sight of the interconnections between those pieces. The term system is often used quite loosely; however, it is instructive to consider the technical definition. The scientific roots of the term date to the 1700s when physical chemists were trying to understand the nature of thermodynamics—heat energy and how its movement causes things to happen.
The river, mountains, forest, and other biota in this photograph of the Alaska Peninsula National Wildlife Refuge are part of a single, large, complex system. The forest alone is a smaller system and so is the river. A tree, a salmon in the river, and an eagle and its nest are all examples of subsystems.
A system is any portion of the universe that can be separated from the rest of the universe for the purpose of observing changes within it. By saying that a system is any portion of the universe, we mean that the system can be whatever the observer defines it to be. That’s why a system is only conceptual; you define its boundaries for the convenience of your study (Figure 2.1). A system can be large or small, simple or complex. You might choose to study the contents of a laboratory beaker. Or you might observe a lake, a fish, a rock, an ocean, a planet, the solar system, or the human body. A leaf is a system. It is part of a larger system (a tree), which in turn is part of an even larger system (a forest).
The fact that a system can be separated from the rest of the universe means that it has conceptual and physical boundaries that set it apart from its surroundings. The nature of those boundaries is one of the defining characteristics of a system. One important type of system is a closed system—its boundaries permit the exchange of energy but not matter with its surroundings. An example would be a perfectly sealed oven, which would allow the material inside to be heated (exchange of energy) but would not allow any of that material to escape (no exchange of matter).
Figure 2.1.
Another important kind of system is an open system, which can exchange both matter and energy across its boundaries. An island offers a relatively simple example (Figure 2.2). Matter enters the system in the form of precipitation (water) and leaves by flowing into the sea or evaporating back into the atmosphere. Energy enters the system as sunlight and leaves as heat. In the natural environment, open systems are common. Materials and energy enter and leave most natural systems with ease, making them difficult to study because we can’t exert the kinds of controls and limitations that we can in a laboratory situation.
We define systems for the purpose of observing changes in them, which brings us back to the fact that Earth is incredibly complex and huge. It has countless parts and interactions among those parts. There are so many variables that it is difficult to study the planet in its entirety. The system concept allows us to study changes within the Earth system, by limiting the size and complexity of the piece we choose to study without sacrificing the concepts of interaction and interconnection.
This approach can be applied to both natural and artificial (that is, humanmade) systems. Ecologists have used the systems approach for many years; an ecosystem is a system that includes and sustains life—a biologic community, its abiotic surroundings, and the interactions between and among them. Urban geographers and planners can also apply the systems approach to the study of cities; enormous flows of energy and materials occur in cities, and they are similar to natural systems in many respects.
Figure 2.2.
In the text there are examples of natural and artificial systems—a leaf, a tree, a forest; a city; an oven; and so on. Think of these and some more examples, such as a refrigerator, a school, or a bird’s nest. In each case, how does the concept of a system apply? Is the system you are thinking of an open system or a closed system, and why?
The systems approach allows scientists to study Earth as an integrated whole by examining smaller interacting parts, or subsystems. The principal subsystems within the Earth system are the atmosphere, the hydrosphere, the solid Earth (both rock and regolith), and the biosphere. They are like huge reservoirs in which materials and energy are stored for a while before moving to one of the other reservoirs. Each of the four main subsystems can be further subdivided. For example, we can divide the hydrosphere into a number of smaller subsystems, including oceans, glaciers, streams, lakes, and groundwater, each of which acts as a reservoir for water.
What term defined in chapter 1 is often used to refer to the physical or abiotic environment—that is, the atmosphere + the hydrosphere + the solid Earth? ________________
Answer: Geosphere.
Earth as a Closed System
Earth itself approximates a closed system. Energy enters the Earth system as shortwave solar radiation. This energy is used in various biologic and geologic processes; then it leaves the system in the form of longer-wavelength energy, or heat. In a perfectly closed system, no matter crosses the system’s boundaries, but it is not quite true that no matter crosses the boundaries of the Earth system. We lose a small but steady stream of hydrogen and helium atoms from the outermost part of the atmosphere, and we gain some material every day in the form of incoming meteorites. However, the amount of matter that enters or leaves the system on a daily basis is so minuscule compared with its overall mass that Earth essentially functions as a closed system.
When changes are made in one part of a closed system, the results of those changes will eventually affect other parts of the system. This is sometimes called the principle of environmental unity. Earth’s subsystems are in a dynamic state of balance; when there is a change in one subsystem, the change spreads throughout the system as a new state of balance, or equilibrium is established. Sometimes an entire chain of events ensues. An interesting example is El Niño, a climatic phenomenon in which anomalously warm water accumulates off the western coast of South America. The warm surface water inhibits the normal rise of cold, nutrientladen waters from great depths. This reduces the available nutrients in the water, causing fish and coastal birds to die off. The unusually warm sea surface temperature initiates a chain of weather-related events around the globe, including abnormally heavy rains, drought, cyclones, unusually cold or mild winters, flooding, and widespread landslides. During an El Niño event, changes in one part of the system are linked to many changes elsewhere in the ocean, in the atmosphere, on the land, and in the biosphere.
The fact that Earth behaves as a closed system has important implications for those of us who live within its boundaries. By definition, the amount of matter in a closed system is finite. The resources on this planet are all we have and, for the foreseeable future, all we will ever have. We must treat Earth resources with respect and use them wisely and cautiously. Another consequence of living in a closed system is that waste materials remain within the boundaries of the Earth system, so we must deal with whatever consequences are associated with the materials we discard. In a closed system, as environmentalists sometimes say, “There is no ‘away’ to throw things to.”
Pesticides have been detected in Arctic polar bears, even though no agricultural chemicals have ever been used nearby. How does this demonstrate the principle of environmental unity? What are some questions an environmental scientist might want to ask about this situation? ________________
Answer: The principle of environmental unity says that when a change is made in one part of the system, the change spreads into other, interconnected parts of the system. If pesticides are introduced in one part of the Earth system, it should not be surprising to find these chemicals appearing somewhere else in the system. Some important questions: How long would it take pesticides to move to the Arctic and into the polar bear from the locations where they were applied? What processes are responsible for the long-distance transport of pesticides? Do pesticides change, break down, or disappear during the course of the journey? How harmful are pesticides to polar bears and other organisms? We will address these and related questions in later chapters.
Cycles and Reservoirs
It is useful to envision interactions within the Earth system as a series of interrelated cycles—groups of processes that facilitate the movement of materials and energy among Earth’s reservoirs. Much of environmental science is concerned with substances in the environment, how they are stored, how they are cycled among the various subsystems within the Earth system, how they are changed or altered in the process, and how they interact with other substances. You can think of a cycle as a set of two or more interconnected reservoirs, between or among which materials (or energy) move in a cyclic manner. The characteristics of environmental reservoirs—the places where materials and energy accumulate and are stored in the Earth system—are of great interest to environmental scientists.
There are two ways to think about environmental reservoirs. One is to think of a reservoir as a holding tank. In this case, a reservoir is like a container with physical boundaries. For example, an ocean is a reservoir for water. So is a lake or a pond. Another more subtle but also more accurate way of thinking about a reservoir is as a mass of material occurring in a particular type of environment. For example, there is a reservoir of salt in ocean water. There is also a reservoir of inorganic silicon, carbon, nitrogen, and many other substances in ocean water. There is a reservoir of ozone in the atmosphere. There is a reservoir of mercury in fish and a reservoir of pesticides in polar bears. And so on.
