The solid outermost shell of the Earth is called the lithosphere. It includes the crust and the upper, solid part of the mantle. On average, the lithosphere is about 50 kilometers thick beneath the oceans and 70 to 100 kilometers thick under the continents. The continental lithosphere and the oceanic lithosphere differ in composition and behavior. The continental crust floats on the asthenosphere, the viscous upper part of the mantle that lies beneath the lithosphere. The movement of the lithosp