The lithosphere is the rigid outer shell of Earth broken into tectonic plates.
It includes Earth’s crust and the uppermost solid part of the mantle. The lithosphere behaves as a strong, brittle layer compared with the warmer, weaker asthenosphere beneath it.
Tectonic plates are pieces of lithosphere that move slowly over the asthenosphere. Their interactions create earthquakes, volcanoes, mountain ranges, ocean trenches, and new crust at spreading centres.
The lithosphere is not equally thick everywhere. Oceanic lithosphere generally becomes thicker as it cools and moves away from a mid-ocean ridge, while continental lithosphere can include ancient, unusually thick regions called cratons. The lithosphere should not be confused with the crust alone: the crust is only its uppermost component.