Plate Tectonics Essay

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Plate Tectonics

Plate tectonics are a relatively new theory that has revolutionized the way geologists think about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The hypothesis of continental drift was largely developed by the German Alfred Wegener The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, continental drift and sea-floor spreading. Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. Sea-floor
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Either side of a spreading center, weak magnetic anomalies 5-50 km wide and hundreds of kilometers long can be identified. Molten rock cools between diverging plates the magnetic minerals present align themselves with the orientation of the Earth's magnetic field at that time. The polarity of the Earth has changed at regular intervals throughout geological time. Magnetic north has alternated between the Arctic (normal polarity) and the Antarctic (reversed polarity). These long linear strips of magnetic anomalies form a symmetrical pattern either side of a spreading center. A record of the changes in the Earth's magnetic polarity has been established and dated for the Cenozoic and is the basis for magnetostratigraphy. This record, in conjunction with the magnetic stripes found either side of a spreading ridge, allows the rate and pattern of sea floor spreading to be examined. At a convergent boundary two plates are in relative motion towards each other. One of the two plates slides down below the other at an angle of around 45 degrees and is incorporated into the Earth's mantle along a subduction zone. The path of this descending plate can be found from analysis of deep earthquakes and the initial point of descent is marked on the surface by a deep ocean trench

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