Plate TectonicsThe third section of this aspect will about the plate tectonics. Plate tectonics is the theory that pieces of Earth's lithosphere, called plates, move about slowly on top of the asthenosphere. Alfred Wegener said that continents were once joined in a single supercontinent, which then broke into pieces that moved apart. This supercontinent is called Pangaea. Pangaea slowly drifted apart in a process called continental drift. Continental drift is a process of the continents moving slowly across Earth's surface. Wegener's theory was proved by the formation of chains of underwater mountains called mid-ocean ridge. New oceanic crust is created at these ridges as old crust move away in a process called sea-floor spreading. The old oceanic plates sink into the mantle as sea-floor spreading occurs and this is called subduction. Subduction zones are near the edges of oceanic plates. When subduction occurs, the plate bends and form a depression in the ocean floor, which is called a trench.
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Sea-floor spreading creates new oceanic crust at mid-ocean ridges. Subduction destroys old oceanic crust at subduction zones.
Plate motions are the visible part of the process of mantle convection. This convection is also the part of the rock cycle, as I explained in the previous page.
Plate motions are the visible part of the process of mantle convection. This convection is also the part of the rock cycle, as I explained in the previous page.
There are three types of plate boundaries: Divergent boundaries, Convergent boundaries, Transform boundaries
Divergent• Plates move away from each other
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Convergent• Plates come together/Collide
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Transform• Plates slide past each other, moving in opposite directions
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Most mountains form along plate boundaries.