´╗┐Plate TectonicsPlate tectonics is the theory that describes the motion of the Earth's lithosphere. The theory of plate tectonics was developed in the late 1950's and early 60's and was built on the older concepts of the continental drift. One of the most famous advocates of the plate tectonic theory was Alfred Wegener. Seven to Eight major and many other minor tectonic plates make up the Earth's lithosphere. Earthquakes, volcanic activity, mountain building, and oceanic trench formation occur along the plate boundaries. A subduction zone takes place at a convergent boundary where two tectonic plates move toward one another and plate slides underneath the other one. Always involves an oceanic plate sliding beneath either another oceanic plate or a continental plate. Subduction zones are noted for their high rates of earthqukes, volcanism, and mountain building. A divergent plate boundary is an area where two tectonic plates are moving away from eachother. Most divergent boundaries are between oceanic plates and produce rift valleys and sometimes volcanic islands. Over millions of years , the divergent plates have moved many hundreds of kilometers away from both sides of the divergent plate boundary.Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Paleomagnetists can determine past behavior of Earth's magnetic field and the past location of tectonic plates. Paleomagnetists led the revival of the theory of continental drift and its transformation into plate tectonics. Apparent polar wander paths provided the first clear geophyscial evidence for continental drift. Paleomagnetism continues to extend the history of plate tectonics back in time and are applied to the movement of continental fragments. A supercontinent is a large landmass formed by the convergence of multiple continents. Pangea, which existed about 225 million years ago, is the most frequently referenced supercontinent. Eventually Pangea frangmented and the pieces now account for Earth's continents.
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