1. n. [Geology]

The brittle outer layer of the Earth that includes the crust and uppermost mantle. It is made up of six major and several minor tectonic plates that move around on the softer asthenosphere. The lithosphere of the oceans tends to be thinner (in some oceanic areas, less than 50 km [30 miles] thick) and more dense than that of the continents (more than 120 km [70 miles] thick in places like the Himalayas) because of isostasy. The movement of the plates of the lithosphere results in convergence, or collisions, that can form mountain belts and subduction zones, and divergence of the plates and the creation of new crust as material wells up from below separating plates. The lithosphere and asthenosphere are distinguished from the crust, mantle and core of the Earth on the basis of their mechanical behavior and not their composition.

See related terms: active margin,  aulacogen,  collision,  convergence,  orogeny,  passive margin,  plate tectonics,  Wadati-Benioff zone