Continental Crust Facts



  • The Earth’s crust is its hard outer shell.
  • The crust is a thin layer of rock that floats on the mantle. It is made mainly of silicate minerals (minerals made of silicon and oxygen) such as quartz.
  • There are two kinds of crust: oceanic and continental.
  • Oceanic crust is the crust beneath the oceans. It is much thinner – just 7 km thick on average. It is also young, with none being over 200 million years old.
  • Continental crust is the crust beneath the continents. It is up to 80 km thick and mostly old.
  • Continental crust is mostly crystalline ‘basement’ rock up to 3800 million years old. Some geologists think at least half of this rock is over 2500 million years old.
  • It is estimated that approximately one cubic kilometer of new continental crust is probably being created each year.
  • The ‘basement’ rock has two main layers: an upper half of silica-rich rocks such as granite, schist and gneiss, and a lower half of volcanic rocks such as basalt which have less silica. Ocean crust is mostly basalt.
  • Continental crust is created in the volcanic arcs above subduction zones (see converging plates). Molten rock from the subducted plate oozes to the surface over a period of a few hundred thousand years.
  • The boundary between the crust and the mantle beneath it is called the Mohorovicic discontinuity.