Subduction initiates as oceanic lithosphere slides beneath continental crust. Some lithospheric plates consist of both continental and oceanic lithosphere. The lithosphere is subdivided into tectonic plates. The layer under the lithosphere is known as the asthenosphere. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. The fractures are tectonic features indicating stresses in the planet's lithosphere. Extensional tectonics is associated with the stretching and thinning of the crust or the lithosphere. Abyssal hills are formed by stretching of the oceanic lithosphere. This development is presumed to have been linked to the subduction of cold oceanic lithosphere. Later work pointed to tectonic uplift, caused by reheating within the lower lithosphere. These cycles include both the living biosphere and the nonliving lithosphere, atmosphere, and hydrosphere. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The mantle part of the lithosphere consists largely of peridotite. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. AMCG plutonism is generally associated with asthenospheric upwelling under thinned lithosphere.