 Lithosphere, a lithosphere is the rigid, outermost shell of a tristrealtite planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of the rocky planet, the crust, is defined on the basis of its chemistry and mineralogy. The study of past and current formations of landscapes is called geomorphology.