Introduction To Physical Geology

C H A P T E R 1 Geology and the Ear th I magine walking on a rocky shore. 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 2 CHAPTER 1 䊳 1.1 THE SCIENCE OF GEOLOGY GEOLOGY AND THE EARTH Geology is the study of the Earth, including the materials that 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