Earth's Tectonic Plates
Plate tectonics is the theory of the movements of the lithosphere. On Earth, there are seven major plates. Where the plates meet is a boundary. Since the plates are touching, when they either move apart, together, slide past each other, or one slides under another. When they move apart the make tranches, move together they make mountains, sliding past each other makes earthquakes, and when one goes under another it creates trenches. Plates move all the time. So often in fact, that a whole theory has been developed by it. This theory is called Pangea. Pangea is a theory developed by Alfred Wegener, which suggests that the continents move, and that they all fit together at one point, over three hundred million years ago. If his theory is indeed correct, just think of what our planet will look like millions of years from now!