Several huge, moving and shifting crustal plates carry Earth's small continents about. These plates, of which the continents are the raised portions, are part of Earth's lithosphere, which includes Earth's crust and the top rigid layer of its mantle. The lithosphere overlays a deeper "plastic" layer of inner Earth, where high temperature and pressure prevent rocks from solidifying.
Plate movement continually generates fresh lithosphere as molten rock erupts at mid-ocean ridges. Oceanic plate margins are drawn into the mantle and melt at continental edges. As these processes cycle, continents move together and pull apart, oceans shrink and expand, plates collide and form mountain ranges, and island chains appear and vanish.