The Lithosphere

The lithosphere is the upper, rigid layer of the Earth. It consists of the crust and the top of the mantle and it is about 100 km thick.

The lithosphere was discovered by "seismology" , which means listening to the pattern of vibrations from earthquakes. Fast earthquake waves show that the top of the mantle is as rigid as the crust, although chemically it is different. The lithosphere is fragmented into relatively strong pieces, called tectonic plates, which move independently relative to one another ( see tectonic plates ).

Temperatures increase by 35°C for every 1000 m you move down through the lithosphere. Below the lithosphere, in the Earth's mantle, is the hot, soft rock of the asthenosphere ( see Earth's interior ). The boundary between the lithosphere and the asthenosphere occurs at the point where temperatures climb above 1300°C.

Under the middle of the oceans the lithosphere is only a few kilometres thick. Here, the mantle's temperature just below the surface is 1300°C.
Under the continents the lithosphere is thickest - 120 km or so.