What is a lithosphere?
The lithosphere (from the Greek for “rocky” sphere) is the solid outermost shell of a rocky planet. On the Earth, the lithosphere includes the crust and the uppermost layer of the mantle (the upper mantle or lower lithosphere) which is joined to the crust. As the cooling surface layer of the Earth’s convection system, the lithosphere thickens over time. It is fragmented into relatively strong pieces, called tectonic plates (shown in the picture), which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics. The distinguishing characteristic of the lithosphere is not composition, but its flow properties. Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, whereas the asthenosphere (the layer of the mantle below the lithosphere) is heat-softened and accommodates strain through plasti
