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The Dynamic Earth 59 DO NOT EDIT--Changes Must Be Made Through “File Info” Printcode=A Chapter 3 Section 1 The Dynamic The Geosphere Section 2 The Atmosphere Section 3 The Hydrosphere and Biosphere Earth Why It Matters Data from NASA satellites enables scientists to determine such things as ecosystem health and air quality and to increase our knowledge of human impact on the planet. In what ways might satellite observations directly affect your life? CASESTUDY Learn about the important services provided by coastal wetlands in the case study The Storm Surge, Tsunamis, and Coastal Wetlands on page 74. Online enVirOnmental Science HMDScience.com Go online to access additional resources, including labs, worksheets, multimedia, and resources in Spanish. ©Earth Imaging/Stone/Getty Images 58 DO NOT EDIT--Changes must be made through “File info” printcode=a Section 1 The Geosphere Objectives Describe the composition and structure of Earth. Violent eruptions blow the tops off volcanoes, and molten rock from earth’s interior flows across the surface of the planet. Hurricanes batter beaches and change Describe Earth’s tectonic plates. coastlines. earthquakes shake the ground and topple buildings and freeway overpasses. All of these are the result of the dynamic state of planet earth. What Explain the main cause of are the underlying conditions that cause our planet to change constantly? earthquakes and their effects. Identify the relationship Earth as a System between volcanic eruptions and climate change. Earth consists of rock, air, water, and living things that all interact with each other. Scientists divide this system into four parts. As shown in Describe how wind and water Figure 1.1, the four parts are the geosphere (rock), the atmosphere (air), alter Earth’s surface. the hydrosphere (water), and the biosphere (living things). The solid part of Earth that consists of all rock, as well as the soils and loose rocks on Earth’s surface, makes up the geosphere. Most of Key Terms the geosphere is located in Earth’s interior. At the equator, the average geosphere distance through the center of Earth to the other side is 12,756 km. The atmosphere is the mixture of gases, nearly all of which are found in the hydro­sphere first 30 km above Earth’s surface. The hydro­sphere makes up all of the crust water on or near Earth’s surface. Much of this water is in the oceans. mantle Water is also found in the atmosphere, on land, and in the soil. The core biosphere is made up of parts of the geosphere, the atmosphere, and the lithosphere hydro sphere. The biosphere is the part of Earth where life exists. It is a asthenosphere thin layer of living organisms found at Earth’s surface and extending from tectonic­plate about 9 km above the surface down to the bottom of the ocean. chemical­weathering erosion Figure 1.1 Earth As a System Earth is an integrated system that consists of the geosphere, the atmosphere, the hydrosphere, and the biosphere (inset). Chapter 3: The Dynamic Earth 59 DO NOT EDIT--Changes must be made through “File info” printcode=a Discovering Earth’s Interior Studying the Earth beneath our feet is not easy. The deepest well that has been drilled into Earth’s interior is only about 12 km deep. An alternative method must be used to study the interior of Earth. Scientists can use seismic waves to learn about Earth’s interior. These waves travel through Earth’s interior during an earthquake. If you have ever tapped a melon to see if it is ripe, you know that the state of the melon’s interior affects the sound you detect. Similarly, a seismic wave is altered by the nature of the material through which it travels. As shown in Figure­1.2, seismologists measure changes in the speed and direction of seismic waves that pen- etrate the interior of the planet. By doing this, seismologists have learned that Earth is made up of dif ferent layers and have inferred from the data what substances make up each layer. The­Composition­of­the­Earth Scientists divide Earth into three layers—the crust, the mantle, and the core—based on their composition. These layers are composed of progres- sively denser materials toward the center of the Earth. Figure­1.3 shows a cross section of Earth. Earth’s thin crust is composed almost entirely of light elements. The crust makes up less than 1 percent of Earth’s mass. The crust is Earth’s thinnest layer. It averages about 5 km in thickness beneath the oceans and is 30 km to 35 km thick beneath the continents. Figure 1.2 Seismic Waves Seismologists have measured changes in the speed and direction of seismic waves that travel through Earth’s interior. Through this process, they have learned that Earth is made up of different layers. 60 Unit 1: Introduction to Environmental Science DO NOT EDIT--Changes must be made through “File info” printcode=a Figure 1.3 Earth’s Layers Scientists divide Earth into different layers based on composition and physical properties. The mantle, which is the layer beneath the crust, makes up 68 percent of the mass of Earth. The mantle is approximately 2,900 km thick and is made of rocks of medium density. Earth’s innermost layer is the core. The core, which has a radius of approximately 3,400 km, is composed of the elements having the greatest density. The­Structure­of­the­Earth If we consider the physical properties of each layer, instead of their chemistry, Earth can be divided into five layers. Earth’s outer layer is the lithosphere. It is a cool, rigid layer, 15 km to 300 km thick, that includes the crust and uppermost part of the mantle. It is divided into huge pieces called tectonic plates. The asthenosphere is the layer beneath the lithosphere. The astheno sphere is a pliable, solid layer of the mantle made of rock that flows very slowly and allows tectonic plates to move on top of it. Beneath the asthenosphere is the mesosphere, the lower part of the mantle. Earth’s outer core is a dense liquid layer. The inner core, at the center of CheCk fOr Understanding the Earth, is dense and solid, made up mostly of the metals iron and nickel. Identify Which­of­Earth’s­physical­layers­ The temperature of the inner core is estimated to be between 4,000°C to is­liquid? 5,400°C. It is solid because it is under enormous pressure. Earth’s outer and inner core together make up about one-third of Earth’s mass. Chapter 3: The Dynamic Earth 61 DO NOT EDIT--Changes must be made through “File info” printcode=a Figure 1.4 The Lithosphere Earth’s lithosphere is divided into pieces called tectonic plates. The tectonic plates are moving in different directions and at different speeds. Eurasian plate North American plate Indian plate Pacific plate African plate Nazca South American plate plate Australian plate Antarctic plate Plate Tectonics The lithosphere is divided into pieces called tectonic­plates that glide mg7vs_ear000014aa HMDScience.com 8th pass across the underlying asthenosphere in much the same way a chunk of 08/18/05 Tectonic Plate Boundaries ice drifts across a pond. The continents are located on the tectonic plates cmurphy and slowly, over eons, move around with them. The major plates include the Pacific, North American, South American, African, Eurasian, and Antarctic plates. Figure­1.4 illustrates the major tectonic plates. Plate­Boundaries Much of the geologic activity at the surface of Earth takes place at the boundaries between tectonic plates. Plates may move away from one another, collide with one another, or slip past one another. Enormous forces are generated at tectonic plate boundaries, where the crust is pulled apart, is squeezed together, or is slipping. The forces produced at the boundaries of tectonic plates can cause violent changes. Plate­Tectonics­and­Mountain­Building When tectonic plates collide, the crust becomes thicker, is pushed up, buckles and folds, and eventually forms a mountain range. As shown in Figure­1.5, the Himalaya Mountains in south-central Asia began to form when the Eurasian tectonic plate and the Indian tectonic plate began to push into each other about 50 million years ago. 62 Unit 1: Introduction to Environmental Science DO NOT EDIT--Changes must be made through “File info” printcode=a Earthquakes Figure 1.5 A fault is a break in Earth’s crust along which blocks of the crust slide rela- Plate Collisions The Himalaya tive to one another. When rocks that are under stress suddenly slip along Mountains are still growing today a fault, a series of vibrations is set off. These vibrations of Earth’s crust because the tectonic plates caused by slippage along a fault are known as earthquakes. Earthquakes containing Asia and the tectonic plate are occurring all the time, but many are so small that we cannot feel containing India continue to collide. them. Other earthquakes are enormous movements of the Earth’s crust that cause widespread damage. The Richter scale is used by scientists to quantify the amount of en- ergy released by an earthquake. The measure of the energy released by an earthquake is called magnitude. The smallest magnitude that can be felt is approximately 2.0, and the largest magnitude that has ever been recorded is 9.5. Each increase of magnitude by one whole number indi- cates the release of about 30 times more energy than the whole number below it. For example, an earthquake of magnitude 6.0 releases 30 times the energy of an earthquake of magnitude 5.0. Earthquakes that cause widespread damage have magnitudes of 7.0 and greater.
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