Continental Drift Theory
Alfred Wegener, a German meteorologist, proposed the “Continental Drift Theory” in 1912. This was regarding the distribution of the oceans and the continents.
- According to Wegener, all the continents formed a single continental mass, a mega ocean surrounded by the same. The supercontinent was named PANGAEA, meaning all earth.
- The mega-ocean was called PANTHALASSA, meaning all water. He argued that, around 200 million years ago, the supercontinent, Pangaea, began to split.
- Pangaea first broke into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively. Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist today.
PLATE TECTONICS THEORY
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In 1967, McKenzie and Parker and Morgan independently collected the available ideas and came out with another concept termed Plate Tectonics.
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A tectonic plate (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
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Plates move horizontally over the asthenosphere as rigid units. The lithosphere includes the crust and top mantle with its thickness range varying between 5-100 km in oceanic parts and about 200 km in the continental areas.
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A plate may be referred to as the continental plate or oceanic plate depending on which of the two occupy a larger portion of the plate. Pacific plate is largely an Oceanic plate whereas the Eurasian plate may be called a Continental plate.
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The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates.