Plate Tectonics

             Plate tectonics is a recently developed science, and it can be used to explain a lot of phenomena on the Earth, such as earthquakes. There are actually two big fundamental theories of plate tectonics. One of the basic theories is called continental drift, and the other one is the theory of seafloor spreading. The theory of continental drift can not explain the power source of moving continents, so the theory is not complete. The theory of seafloor spreading is only focusing on the movements under water, and the theory still cannot find the evidence of the power source. After having better understanding the activities of volcanoes, earthquakes and terrestrial magnetism, the theory of plate tectonics was introduced about 30 years ago.
             The most obvious evidence of continental drifting is the remarkable fit of the South American and African continents. By recombining present continents, the Pangaea is still clearly seen. The graph bellow compares the Pangaea to the present continents.
             In 1912, Lothar Wegener introduced the theory of continental drift, which based on the evidences of geologic structures and plant and animal fossils. Here are three proofs that support the theory of continental drift:
             ƒÜ The same glacier remains in Africa, South America, Antarctica, Australia and Indian sub-continent.
             ƒÜ The coal deposits from identical age in the areas mentions at previous point.
             ƒÜ The occurrences of distinctive fossil ferns (Glossopteris) in now-polar regions.
             At the time when Wegener introduced his theory, there were not enough evidences to show what kind of force can move those giant continents over such a long distance. The theory of continental drift was not widely accepted at that time. After 1950, the new discoveries of studies of the Earth's ancient magnetic field and the ocean geology rekindled interest in the theory of continental drift. And the theory of seafloor spreading is der
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