Crust ( geology ) - wikipedia Crust ( geology ) Geologic provinces of the World ( USGS ) Shield Platform Orogen Basin Large igneous province Extended crust Oceanic crust : 0 -- 20 Ma 20 -- 65 Ma > 65 Ma In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet or natural satellite, which is chemically distinct from the underlying mantle. The crusts of Earth, Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles. The Earth 's crust is composed of distinctly different continental crust and oceanic crust, which have different chemical compositions and physical properties, and which were formed by different geological processes. Contents 1 Earth 's crust 1.1 Composition 2 Moon 's crust 3 See also 4 Notes 5 References 6 External links Earth 's crust The internal structure of Earth The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying 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 occupies less than 1 % of Earth 's volume. The crust of the Earth is of two distinctive types : oceanic and continental. The oceanic crust is 5 km ( 3 mi ) to 10 km ( 6 mi ) thick and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km ( 20 mi ) to 50 km ( 30 mi ) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust. Both the continental and oceanic crust `` float '' on the mantle. Because the continental crust is thicker, it extends both to greater elevations and greater depth than the oceanic crust. The slightly lower density of felsic continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, water runs off the continents and collects above the oceanic crust. Because of the change in velocity of seismic waves it is believed that beneath continents at a certain depth continental crust ( sial ) becomes close in its physical properties to oceanic crust ( sima ), and the transition zone is referred to as the Conrad discontinuity. The temperature of the crust increases with depth, 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 crust and underlying relatively rigid uppermost mantle make up the lithosphere. Because of convection in the underlying plastic ( although non-molten ) upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. 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. Plates in the crust of Earth Partly by analogy to what is known about the Moon, Earth is considered to have differentiated from an aggregate of planetesimals into its core, mantle and crust within about 100 million years of the formation of the planet, 4.6 billion years ago. During the Hadean, the primordial crust was very thin and was probably destroyed by much more vigorous plate tectonics, volcanic activity and significant asteroid impacts, which were much more common in the early stages of the solar system. Earth has probably always had some form of basaltic crust, but the age of the oldest oceanic crust today is only about 200 million years. In contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4.28 billion years and have been found in the Narryer Gneiss Terrane in Western Australia, in the Acasta Gneiss in the Northwest Territories on the Canadian Shield, and on other cratonic regions such as those on the Fennoscandian Shield. Some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earth 's continental crust has been estimated to be about 2.0 billion years. Most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth and so are not readily destroyed by subduction. Formation of new continental crust is linked to periods of intense orogeny ; these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms in part by aggregation of island arcs including granite and metamorphic fold belts, and it is preserved in part by depletion of the underlying mantle to form buoyant lithospheric mantle. Composition Main articles : Abundance of elements in Earth 's crust and Goldschmidt classification Abundance ( atom fraction ) of the chemical elements in Earth 's upper continental crust as a function of atomic number. The rarest elements in the crust ( shown in yellow ) are not the heaviest, but are rather the siderophile ( iron - loving ) elements in the Goldschmidt classification of elements. These have been depleted by being relocated deeper into Earth 's core. Their abundance in meteoroid materials is higher. Additionally, tellurium and selenium have been depleted from the crust due to formation of volatile hydrides. The continental crust has an average composition similar to that of andesite. The most abundant minerals in Earth 's continental crust are feldspars, which make up about 41 % of the crust by weight, followed by quartz at 12 %, and pyroxenes at 11 %. Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle. Although the continental crust comprises only about 0.6 weight percent of the silicate on Earth, it contains 20 % to 70 % of the incompatible elements. Most Abundant Elements of Earth 's Crust Approximate % by weight O 46.6 Si 27.7 Al 8.1 Fe 5.0 Ca 3.6 Na 2.8 2.6 Mg 1.5 Oxide Percent SiO 60.6 Al O 15.9 CaO 6.4 MgO 4.7 Na O 3.1 Fe as FeO 6.7 K O 1.8 TiO 0.7 P O 0.1 All the other constituents except water occur only in very small quantities and total less than 1 %. Estimates of average density for the upper crust range between 2.69 and 2.74 g / cm and for lower crust between 3.0 and 3.25 g / cm. Moon 's crust Main article : Geology of the Moon A theoretical protoplanet named `` Theia '' is thought to have collided with the forming Earth, and part of the material ejected into space by the collision accreted to form the Moon. As the Moon formed, the outer part of it is thought to have been molten, a `` lunar magma ocean. '' Plagioclase feldspar crystallized in large amounts from this magma ocean and floated toward the surface. The cumulate rocks form much of the crust. The upper part of the crust probably averages about 88 % plagioclase ( near the lower limit of 90 % defined for anorthosite ) : the lower part of the crust may contain a higher percentage of ferromagnesian minerals such as the pyroxenes and olivine, but even that lower part probably averages about 78 % plagioclase. The underlying mantle is denser and olivine - rich. The thickness of the crust ranges between about 20 and 120 km. Crust on the far side of the Moon averages about 12 km thicker than that on the near side. Estimates of average thickness fall in the range from about 50 to 60 km. Most of this plagioclase - rich crust formed shortly after formation of the moon, between about 4.5 and 4.3 billion years ago. Perhaps 10 % or less of the crust consists of igneous rock added after the formation of the initial plagioclase - rich material. The best - characterized and most voluminous of these later additions are the mare basalts formed between about 3.9 and 3.2 billion years ago. Minor volcanism continued after 3.2 billion years, perhaps as recently as 1 billion years ago. There is no evidence of plate tectonics. Study of the Moon has established that a crust can form on a rocky planetary body significantly smaller than Earth. Although the radius of the Moon is only about a quarter that of Earth, the lunar crust has a significantly greater average thickness. This thick crust formed almost immediately after formation of the Moon. Magmatism continued after the period of intense meteorite impacts ended about 3.9 billion years ago, but igneous rocks younger than 3.9 billion years make up only a minor part of the crust. See also Geology portal Eduction Notes Jump up ^ Robinson, Eugene C. ( January 14, 2011 ). `` The Interior of the Earth ''. U.S. Geological Survey. Retrieved August 30, 2013. Jump up ^ Structure of the Earth. The Encyclopedia of Earth. March 3, 2010 Jump up ^ Peele, Robert ( 1911 ). `` Boring ''. In Chisholm, Hugh. Encyclopædia Britannica. 4 ( 11th ed. ). Cambridge University Press. p. 251. Jump up ^ Earth. Channel4.com. Retrieved on 2011 - 12 - 13. Jump up ^ Erickson, Jon ( 2014 ). Historical Geology : Understanding Our Planet 's Past. Infobase Publishing. p. 8. ISBN 1438109644. Retrieved 28 September 2017. Jump up ^ `` Team finds Earth 's ' oldest rocks ' ''. BBC News. 2008 - 09 - 26. Retrieved 2010 - 03 - 27. Jump up ^ 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 Jump up ^ 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 Jump up ^ 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 Jump up ^ Anderson, Robert S. ; Anderson, Suzanne P. ( 2010 ). Geomorphology : The Mechanics and Chemistry of Landscapes. Cambridge University Press. p. 187. Jump up ^ `` Structure and composition of the Earth ''. Australian Museum Online. Retrieved 2007 - 09 - 14. Jump up ^ Wieczorek, M.A. & Zuber, M.T. ( 2001 ), `` The composition and origin of the lunar crust : Constraints from central peaks and crustal thickness modeling '', Geophysical Research Letters, 28 ( 21 ) : 4023 -- 4026, Bibcode : 2001GeoRL... 28.4023 W, doi : 10.1029 / 2001GL012918 Jump up ^ Herald Hiesinger and James W. Head III ( 2006 ). `` New views of Lunar geoscience : An introduction and overview '' ( PDF ). Reviews in Mineralogy & Geochemistry. 60 : 1 -- 81. doi : 10.2138 / rmg. 2006.60. 1. References Condie, Kent C. ( 1989 ). `` Origin of the Earth 's Crust ''. Palaeogeography, Palaeoclimatology, Palaeoecology ( Global and Planetary Change Section ). 75 : 57 -- 81. doi : 10.1016 / 0031 - 0182 ( 89 ) 90184 - 3. External links The Wikibook Historical Geology has a page on the topic of : Structure of the Earth USGS Crustal Thickness Map `` Crust of the Earth ''. Encyclopedia Americana. 1920. `` Geology ''. 1911 Encyclopædia Britannica. Structure of the Earth Shells Crust Lithosphere Mesosphere Mantle Asthenosphere Lithospheric mantle Subcontinental lithospheric mantle Oceanic lithospheric mantle Outer core Inner core Discontinuities Conrad ( continental crust ) Mohorovičić ( crust -- mantle ) Lehmann ( upper mantle ) Gutenberg ( mantle -- core ) Lehmann ( core ) Arguments Plate tectonics GND : 4015169 - 4 NDL : 00573002 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Crust_(geology)&oldid=808568151 '' Categories : Plate tectonics Structure of the Earth Hidden categories : Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference All articles with dead external links Articles with dead external links from February 2017 Articles with permanently dead external links Wikipedia indefinitely semi-protected pages Wikipedia articles incorporating a citation from the Encyclopedia Americana with a Wikisource reference Wikipedia articles with GND identifiers Talk View source Contents About Wikipedia Адыгэбзэ Afrikaans Ænglisc Aragonés Azərbaycanca Bân - lâm - gú Basa Banyumasan Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Brezhoneg Català Čeština Cymraeg Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Frysk Furlan Gaeilge Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Interlingua Íslenska Italiano עברית Basa Jawa ქართული Kiswahili Latviešu Lietuvių Limburgs Magyar Македонски മലയാളം მარგალური Bahasa Melayu Монгол Nederlands Nedersaksies 日本 語 Norsk Norsk nynorsk Occitan Oromoo ਪੰਜਾਬੀ پنجابی Plattdüütsch Polski Português Română Русский Simple English Slovenčina Slovenščina Soomaaliga Српски / srpski Srpskohrvatski / српскохрватски Basa Sunda Suomi Svenska தமிழ் Татарча / tatarça ไทย Türkçe Українська اردو Tiếng Việt Walon 粵語 中文 Edit links This page was last edited on 3 November 2017, at 17 : 30. 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Question: whats the composition of the earth's crust
Answer: an average composition similar to that of andesite