Plate tectonics refers to the movement of the rigid plates around the surface of Earth. The outer portion of the planet, or lithosphere, is relatively rigid because it is relatively cold. The lithosphere varies in thickness but is typically a hundred or so kilometers thick. It includes the upper mantle and both the continental and oceanic crust. The mantle’s convective motions break the lithosphere into plates and move them around the surface of the planet. These plates may move away from, move by, or collide with each other. This process forms ocean basins, shifts continents, and pushes up mountains.
