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Facts about the Continental Crust for Kids

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because there is more felsic, or granitic, bulk composition, which lies in contrast to the oceanic crust, called sima because of the mafic or basaltic rock.

  • Consisting mostly of granitic rock, continental crust has a density of about 2.7 g/cm and is less dense than the material of the Earth’s mantle, which consists of mafic rock.
  • Continental crust is also less dense than oceanic crust, though it is considerably thicker; mostly 25 to 70 km versus the average oceanic thickness of around 7–10 km.
  • Because continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life.
  • If Earth were like the other silicate planets and lacked the duality of oceanic and continental crust, our planet would be a very different place and the evolution of Homo sapiens and civilization might have been impossible.
  • This process has been and continues today primarily as a result of the volcanism associated with subduction.
  • Because continental crust is less dense than oceanic crust, when active margins of the two meet in subduction zones, the oceanic crust is typically subducted back into the mantle.
  • Continental crust is rarely subducted.
  • The high temperatures and pressures at depth, often combined with a long history of complex distortion, cause much of the lower continental crust to be metamorphic – the main exception to this being recent igneous intrusions.
  • Continental crust is also lost through erosion and sediment subduction, tectonic erosion of forearcs, delamination, and deep subduction of continental crust in collision zones.
  • Many theories of crustal growth are controversial, including rates of crustal growth and recycling, whether the lower crust is recycled differently than the upper crust and over how much of Earth history plate tectonics has operated and so could be the dominant mode of continental crust formation and destruction.
  • It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time.