Earth’s Crust

Synonym: Crust

The Earth’s crust is the solid zone above the Mohorovicic discontinuity, and it is part of the lithosphere. The crust is composed of solid rocks and is divided into the upper crust and lower crust by the Conrad discontinuity. The upper crust is a silica-aluminium-rich layer, and the lower crust is a silica-magnesium-rich layer. The crust can be divided into the continental crust, transitional crust and oceanic crust. The continental crust contains silica-magnesium-rich and silica-aluminium-rich rocks and is 20–70 km thick. The oceanic crust often lacks the silica-aluminium-rich layer and is only 5–8 km thick in the deep ocean. The solid rock that makes up the crust is both elastic and plastic. Crustal movement causes the crust to deform and rupture, and most tectonic earthquakes occur in the crust. As such, the Earth’s crust is the main region of study in geology and seismology. Crustal tectonic movements and seismic activity are closely related to the deeper processes...