What Do the Crust and Upper Mantle Form?

The crust and upper mantle of the Earth form the lithosphere. The lithosphere is about 62 miles thick. The part of the lithosphere that supports the continents is thicker than the part of the lithosphere that supports the oceans.

The asthenosphere, a viscous layer between the crust and the upper mantle, is also part of the lithosphere.

Unlike the lithospheres of the other terrestrial planets, the Earth's lithosphere is fluid and separated into tectonic plates. These plates can move, albeit slowly, because of the heat found in the upper mantle. Because the crust is brittle, movements of these plates cause earthquakes and the eruptions of volcanoes.