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"Geology and the Earth" C tH tA tP tT tE tR 1 Geology and the Earth. You can see the pounding surf, hear stones clink together as waves recede, feel the wind blowing in your hair. But the cliffs don't move and the ground doesn't shake. Even though the Earth appears to be a firm foundation beneath your feet, it is a dynamic planet. Continents slowly shift position; mountains rise and then erode away. These motions escape casual observation because they are generally slow, although every year events such as volcanic eruptions and earthquakes remind us that geologic change can be rapid. A storm-driven wave crashes against the Oregon coast. (H. Richard Johnston Tony Stone Images) 1 CHAPTER 1 GEOLOGY AND THE EARTH 1.1 THE SCIENCE OF GEOLOGY Geology is the study of the Earth, including the materials it is made of, the physical and chemical changes that occur on its surface and in its interior, and the history of the planet and its life forms. THE EARTH AND ITS MATERIALS The Earth's radius is about 6370 kilometers, nearly one and a half times the distance from New York to Los Angeles (Fig. 1-1). If you could drive a magical vehicle from the center of the Earth to the surface at 100 kilometers per hour, the journey would take more than two and a half days. Most of the Earth is composed of rocks. Rock outcrops form some of our planet's most spectacular scenery: white chalk cliffs, pink sandstone arches, and the grey granite of Yosemite Valley. Rocks, in turn, are composed of minerals (Fig. 1-2). Although more than 3500 different minerals exist, fewer than a dozen are common. Geologists study the origins, properties, and compositions of both rocks and minerals. Geologists also explore the Earth for the resources needed in our technological world: fossil fuels such as coal, petroleum, and natural gas; mineral resources such as metals; sand and gravel; and fertilizers. Some search for water in reservoirs beneath Earth's surface. Figure 1-2 This granite rock is composed of different minerals, primarily quartz, feldspar, and hornblende. The mineral grains are a few millimeters in diameter. INTERNAL PROCESSES Processes that originate deep in the Earth's interior are called internal processes. These are the driving forces that raise mountains, cause earthquakes, and produce volcanic eruptions. Builders, engineers, and city planners might consult geologists, asking, "What is the probability that an earthquake or a volcanic eruption will damage our city? Is it safe to build skyscrapers, a dam, or a nuclear waste repository in the area?" BIOSPHERE ALL life is concentrated at or within a few kilometers of the surface. HYDROSPHERE Deep ocean floor 5 km deep. Fresh water and ice exist on land Earth. ATMOSPHERE 99% of atmosphere lies within 30 km of the surface Radius 6370 km Figure 1-1 Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. 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