Earth's crust

The Earth's crust is a thin shell on the outside of the Earth, accounting for less than 1% of Earth's volume. It is the top component of lithosphere: a division of Earth's layers that includes the crust and the upper part of the mantle.[1] The lithosphere is broken into tectonic plates that move, allowing heat to escape from the interior of the Earth into space.

The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is significantly denser than the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.

The crust of the Earth is of two distinctive types:

  1. Oceanic: 5 km (3 mi) to 10 km (6 mi) thick[2] and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.
  2. Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite.

Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle. This is isostasy, and it's also one of the reasons continental crust is higher than oceanic: continental is less dense and so "floats" higher. As a result, water pools in above the oceanic crust, forming the oceans.

The temperature of the crust increases with depth,[3] reaching values typically in the range from about 200 °C (392 °F) to 400 °C (752 °F) at the boundary with the underlying mantle. The temperature increases by as much as 30 °C (54 °F) for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust.[4]

See also

References

  1. Robinson, Eugene C. (January 14, 2011). "The Interior of the Earth". U.S. Geological Survey. Retrieved August 30, 2013.
  2. Structure of the Earth. The Encyclopedia of Earth. March 3, 2010
  3. Peele, Robert (1911). "Boring" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. 4 (11th ed.). Cambridge University Press. p. 251.
  4. Earth. Channel4.com. Retrieved on 2011-12-13.
  5. R. L. Rudnick and S. Gao, 2003, Composition of the Continental Crust. In The Crust (ed. R. L. Rudnick) volume 3, pp. 1–64 of Treatise on Geochemistry (eds. H. D. Holland and K. K. Turekian), Elsevier-Pergamon, Oxford ISBN 0-08-043751-6
  6. Anderson, Robert S.; Anderson, Suzanne P. (2010). Geomorphology: The Mechanics and Chemistry of Landscapes. Cambridge University Press. p. 187. ISBN 978-1-139-78870-0.
  7. "Structure and composition of the Earth". Australian Museum Online. Retrieved 2007-09-14.
  8. Erickson, Jon (2014). Historical Geology: Understanding Our Planet's Past. Infobase Publishing. p. 8. ISBN 978-1438109640. Retrieved 28 September 2017.
  9. "Team finds Earth's 'oldest rocks'". BBC News. 2008-09-26. Retrieved 2010-03-27.
  10. P. J. Patchett and S. D. Samson, 2003, Ages and Growth of the Continental Crust from Radiogenic Isotopes. In The Crust (ed. R. L. Rudnick) volume 3, pp. 321–348 of Treatise on Geochemistry (eds. H. D. Holland and K. K. Turekian), Elsevier-Pergamon, Oxford ISBN 0-08-043751-6
  11. A. I. S. Kemp and C. J. Hawkesworth, 2003, Granitic Perspectives on the Generation and Secular Evolution of the Continental Crust. In The Crust (ed. R. L. Rudnick) volume 3, pp. 349–410 of Treatise on Geochemistry (eds. H. D. Holland and K. K. Turekian), Elsevier-Pergamon, Oxford ISBN 0-08-043751-6
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