Crust (geology)

In geology, a crust is the outermost layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than its deeper layers. The crust of the Earth is composed mainly of basalt and granite. It is cooler and more rigid than the deeper layers of the mantle and core.

On stratified planets, such as Earth, the lithosphere is floating on fluid interior layers. Because of convection in the plastic, although non-molten, upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. Oceanic crust is different from continental. The oceanic crust (sima) is 5 to 10 km thick and is composed primarily of basalt. The continental crust (sial) is 20-70 km deep and is composed of mostly less dense rocks, particularly granite. The crust's temperature ranges from the air temperature to about 900°C near the upper mantle. In all Earth's crust occupies less than 1% of Earth's volume.