Plate tectonics is the theory that pieces of the Earth's lithosphere, called plate, move slowly on top of the asthenosphere. This explains the formation and movement of Earth's plates. Alfred Wegener, a German scientist, hypothesized that once upon a time, the continents were joined together, and then broke off into smaller pieces. This land was called Pangaea. Continental drift is when continents move slowly across Earth's surface. Seafloor spreading is the process in which new oceanic crust is created at mid-ocean ridges as older crust moves away. Mid-ocean ridges are huge cracks in the crust where magma is pulled upwards. As seafloor spreading occurs, old oceanic plates sink into the mantle, which is called subduction. At subduction zones, the old oceanic plates get destroyed. There are three kinds of plate boundaries, convergent, divergent, and transform plate boundaries.
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