|MadSci Network: Earth Sciences|
The plate tectonics theory states that the outermost layer of the Earth (the first 100 km, in average) is divided in plates, that we call lithospheric plates. The interaction of these plates (colision, spreading, displacement) are part of the process of plate tectonics. The plate tectonics evolved from an old idea postulated by Alfred Wegener, by the beginning of the century, called continental drift. This early theory stated that the continents were joined together in the past in a supercontinent called Pangea, that broke up into two big masses: Gondwana and Laurasia. Some problems with this theory, in particular the inexistence of a mecanism that could explain the enormous forces that should be necessary to move the plates, contributed to the theory to be put apart for decades. In the early 1960's, some geophysical discoveries evidenced that this theory should be revisited, among them: - the bathymetry showed that the ocean floor have many topographic features, and additionally, the oceanic crust was much younger than expected (this was discovered by the thickness of the sediments; if the oceanic crust had the 3-4 billion years that was supposed, there should be many km of sediments deposited, what was not true by the measurements); - the magnetic patterns in the seafloor; - the distribution of earthquakes along some zones, and not globally distributed. So, the bathymetry helped to revisit the continental drift theory, and reformulate to evolve to the plate tectonic theory. If you need any further explanation, please feel free to contact me. Eder C. Molina email@example.com Dept. of Geophysics Institute of Astronomy and Geophysics University of Sao Paulo - USP BRASIL
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