TAILIEUCHUNG - Encyclopedia of Global Resources part 103

Encyclopedia of Global Resources part 103 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 948 Plate tectonics Global Resources Plate tectonics Category Geological processes and formations The theory of plate tectonics provides an explanation for the present-day structure of the outer part of the Earth. It provides a framework for understanding the global distribution of mountain building earthquake activity and volcanism the geology of ocean basins various associations of igneous metamorphic and sedimentar y rocks and the formation and location of mineral resources. Background Plate tectonic theory is based on a concept of the Earth in which a rigid outer shell the lithosphere lies above a hotter weaker partially molten part of the mantle known as the asthenosphere. The thickness of the lithosphere varies between 50 and 150 kilometers and it consists of crust and the underlying upper mantle. The asthenosphere extends from the base of the lithosphere to a depth of about 700 kilometers. The brittle lithosphere is broken into a pattern of internally rigid plates that move horizontally across the Earth s surface relative to each other. Seven major plates and a number of smaller ones have been distinguished and they grind and scrape against one another as they move independently similar to chunks of ice on water. Most of the Earth s dynamic activity including earthquakes and volcanism occurs along plate boundaries and the global distribution of these tectonic phenomena delineates the boundaries of the plates. Plate Boundaries and Motion Geophysical data geological obser vations and theoretical deductions support the existence of three basic types of plate boundaries divergent boundaries where adjacent plates move apart diverge from each other convergent boundaries where adjacent plates move toward each other and transform boundaries where plates slip past one another in a direction parallel to their common boundar y. The velocity with which plates move varies from plate to plate and within portions of the same plate ranging from two to twenty centimeters per

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