Editing Carbon (section)

===Occurrence===
[[File:GraphiteOreUSGOV.jpg|thumb|Graphite ore, shown with a penny for scale]]
[[File:Rough diamond.jpg|thumb|Raw diamond crystal]]
[[File:Annual mean sea surface dissolved inorganic carbon for the 1990s (GLODAP).png|thumb|"Present day" (1990s) sea surface [[dissolved inorganic carbon]] concentration (from the [[GLODAP]] [[climatology]])]]

Carbon is the [[abundance of the chemical elements|fourth most abundant chemical element]] in the observable universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the [[celestial body's atmosphere|atmospheres]] of most planets.<ref name="Hoover-2014"/> Some [[meteorite]]s contain microscopic diamonds that were formed when the Solar System was still a [[protoplanetary disk]].<ref name="Lauretta-2006">{{cite book |last1=Lauretta |first1=D.S. |last2=McSween |first2=H.Y. |title=Meteorites and the Early Solar System II |publisher=University of Arizona Press |series=Space science series |year=2006 |isbn=978-0-8165-2562-1 |page=199 |url=https://books.google.com/books?id=FRc2iq9g9pkC&pg=PA199 |access-date=2017-05-07 |url-status=live |archive-url=https://web.archive.org/web/20171122173131/https://books.google.com/books?id=FRc2iq9g9pkC&pg=PA199 |archive-date=2017-11-22}}</ref> Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.<ref>{{cite book |author=Mark, Kathleen |url=https://archive.org/details/meteoritecraters0000mark_o3c4 |title=Meteorite Craters |date=1987 |publisher=University of Arizona Press |isbn=978-0-8165-0902-7 |url-access=registration}}</ref>

In 2014 [[NASA]] announced a [http://www.astrochem.org/pahdb/ greatly upgraded database] for tracking [[polycyclic aromatic hydrocarbons]] (PAHs) in the universe. More than 20% of the carbon in the universe may be associated with PAHs, complex compounds of carbon and hydrogen without oxygen.<ref>{{cite news |url=http://scitechdaily.com/online-database-tracks-organic-nano-particles-across-universe/ |title=Online Database Tracks Organic Nano-Particles Across the Universe |work=Sci Tech Daily |date=February 24, 2014 |access-date=2015-03-10 |url-status=live |archive-url=https://web.archive.org/web/20150318034957/http://scitechdaily.com/online-database-tracks-organic-nano-particles-across-universe/ |archive-date=March 18, 2015}}</ref> These compounds figure in the [[PAH world hypothesis]] where they are hypothesized to have a role in [[abiogenesis]] and formation of life. PAHs seem to have been formed "a couple of billion years" after the [[Big Bang]], are widespread throughout the universe, and are associated with [[star formation|new stars]] and [[exoplanet]]s.<ref name="Hoover-2014">{{cite web |last=Hoover |first=Rachel |title=Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That |url=http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |date=21 February 2014 |work=[[NASA]] |access-date=2014-02-22 |url-status=live |archive-url=https://web.archive.org/web/20150906061428/http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |archive-date=6 September 2015}}</ref>

It has been estimated that the solid earth as a whole contains 730 ppm of carbon, with 2000 ppm in the core and 120 ppm in the combined mantle and crust.<ref>William F McDonough [http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf The composition of the Earth] {{webarchive|url=https://web.archive.org/web/20110928074153/http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf|date=2011-09-28}} in {{cite book |title=Earthquake Thermodynamics and Phase Transformation in the Earth's Interior |date=2000 |isbn=978-0-12-685185-4 |last1=Majewski |first1=Eugeniusz|publisher=Elsevier Science }}</ref> Since the mass of the earth is {{val|5.972|e=24|u=kg}}, this would imply 4360 million [[gigatonne]]s of carbon. This is much more than the amount of carbon in the oceans or atmosphere (below).

In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 900&nbsp;gigatonnes of carbon — each ppm corresponds to 2.13&nbsp;Gt) and dissolved in all water bodies (approximately 36,000&nbsp;gigatonnes of carbon). Carbon in the [[biosphere]] has been estimated at 550&nbsp;gigatonnes but with a large uncertainty, due mostly to a huge uncertainty in the amount of terrestrial deep [[subsurface bacteria]].<ref>{{cite journal |display-authors=etal |last1=Yinon Bar-On |title=The biomass distribution on Earth |journal=[[PNAS]] |volume=115 |issue=25 |pages=6506–6511 |date=Jun 19, 2018 |doi=10.1073/pnas.1711842115 |pmid=29784790 |pmc=6016768 |bibcode=2018PNAS..115.6506B |doi-access=free}}</ref> [[Hydrocarbons]] (such as coal, petroleum, and natural gas) contain carbon as well. Coal "reserves" (not "resources") amount to around 900&nbsp;gigatonnes with perhaps 18,000 Gt of resources.<ref>{{cite journal |title=Fire in the hole: After fracking comes coal |journal=[[New Scientist]] |volume=221 |issue=2956 |date=2014-02-15 |pages=36–41 |url=https://www.newscientist.com/article/mg22129560.400-fire-in-the-hole-after-fracking-comes-coal.html?full=true |author=Fred Pearce |author-link=Fred Pearce |url-status=live |archive-url=https://web.archive.org/web/20150316021625/http://www.newscientist.com/article/mg22129560.400-fire-in-the-hole-after-fracking-comes-coal.html?full=true |archive-date=2015-03-16 |bibcode=2014NewSc.221...36P |doi=10.1016/S0262-4079(14)60331-6}}</ref> [[Oil reserves]] are around 150&nbsp;gigatonnes. Proven sources of natural gas are about {{val|175|e=12|u=cubic metres}} (containing about 105 gigatonnes of carbon), but studies estimate another {{val|900|e=12|u=cubic metres}} of "unconventional" deposits such as [[shale gas]], representing about 540 gigatonnes of carbon.<ref>[https://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true "Wonderfuel: Welcome to the age of unconventional gas"] {{webarchive|url=https://web.archive.org/web/20141209231648/http://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true|date=2014-12-09}} by Helen Knight, ''[[New Scientist]]'', 12 June 2010, pp. 44–7.</ref>

Carbon is also found in [[methane hydrates]] in polar regions and under the seas. Various estimates put this carbon between 500, 2500,<ref>[http://news.bbc.co.uk/2/hi/science/nature/3493349.stm Ocean methane stocks 'overstated'] {{webarchive|url=https://web.archive.org/web/20130425211445/http://news.bbc.co.uk/2/hi/science/nature/3493349.stm|date=2013-04-25}}, BBC, 17 Feb. 2004.</ref> or 3,000 Gt.<ref>[https://www.newscientist.com/article/mg20227141.100 "Ice on fire: The next fossil fuel"] {{webarchive|url=https://web.archive.org/web/20150222041938/http://www.newscientist.com/article/mg20227141.100|date=2015-02-22}} by [[Fred Pearce]], ''New Scientist'', 27 June 2009, pp. 30–33.</ref>

According to one source, in the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels.<ref>Calculated from file global.1751_2008.csv in {{cite web |url=http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES |title=Index of /ftp/ndp030/CSV-FILES |access-date=2011-11-06 |url-status=dead |archive-url=https://web.archive.org/web/20111022125534/http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/ |archive-date=2011-10-22}} from the [[Carbon Dioxide Information Analysis Center]].</ref> Another source puts the amount added to the atmosphere for the period since 1750 at 879 Gt, and the total going to the atmosphere, sea, and land (such as [[peat bog]]s) at almost 2,000 Gt.<ref>{{cite journal |title=Deep, and dank mysterious |journal=New Scientist |date=Sep 21, 2013 |pages=40–43 |url=https://www.newscientist.com/articleimages/mg21929350.800/1-whats-brown-and-soggy-and-could-save-the-world.html |author=Rachel Gross |url-status=live |archive-url=https://web.archive.org/web/20130921055409/http://www.newscientist.com/articleimages/mg21929350.800/1-whats-brown-and-soggy-and-could-save-the-world.html |archive-date=2013-09-21}}</ref>

Carbon is a constituent (about 12% by mass) of the very large masses of [[carbonate]] rock ([[limestone]], [[dolomite (mineral)|dolomite]], [[marble]], and others). Coal is very rich in carbon ([[anthracite]] contains 92–98%)<ref>{{cite book |title=Coal Mining Technology: Theory and Practice |author=Stefanenko, R. |publisher=Society for Mining Metallurgy |date=1983 |isbn=978-0-89520-404-2}}</ref> and is the largest commercial source of mineral carbon, accounting for 4,000&nbsp;gigatonnes or 80% of [[fossil fuel]].<ref>{{cite journal |first=James |last=Kasting |date=1998 |title=The Carbon Cycle, Climate, and the Long-Term Effects of Fossil Fuel Burning |journal=Consequences: The Nature and Implication of Environmental Change |volume=4 |issue=1 |url=http://gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html |url-status=live |archive-url=https://web.archive.org/web/20081024152448/http://gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html |archive-date=2008-10-24}}</ref>

As for individual carbon allotropes, graphite is found in large quantities in China, Russia, Mexico, Canada, and India.<ref>{{cite book |author1=Wilhelm Frohs |author2=Ferdinand von Sturm |author3=Erhard Wege |author4=Gabriele Nutsch |author5=Werner Handl |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2010 |isbn=9783527306732 |chapter=Carbon, 3. Graphite|publisher=Wiley }}</ref> Natural diamonds occur in the rock [[kimberlite]], found in ancient volcanic "necks", or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Angola. Diamond deposits have also been found in [[Arkansas]], Canada, the Russian Arctic, Brazil, and in Northern and Western Australia.<ref>{{cite book |author1=Otto Vohler |author2=Gabriele Nutsch |author3=Ferdinand von Sturm |author4=Erhard Wege |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2010 |isbn=9783527306732 |language=en |chapter=Carbon, 2. Diamond |doi=10.1002/14356007.n05_n01}}</ref> Diamonds are found naturally, but about 90% of all industrial diamonds used in the U.S. are now manufactured.<ref>{{cite web |author1=Donald Olson |title=Industrial Diamond Statistics and Information |url=https://www.usgs.gov/centers/national-minerals-information-center/industrial-diamond-statistics-and-information |website=USGS |publisher=National Minerals Information Center |language=en}}</ref>

Carbon-14 is formed in upper layers of the troposphere and the stratosphere at altitudes of 9–15&nbsp;km by a reaction that is precipitated by [[cosmic ray]]s.<ref>{{cite web |url=http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/carbondatingback.html |url-status=live |title=Carbon-14 formation |access-date=13 October 2014 |archive-url=https://web.archive.org/web/20150801234723/http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/carbondatingback.html |archive-date=1 August 2015}}</ref> [[Thermal neutron]]s are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton. As such, {{val|1.5|e=-10|u=%}} of atmospheric carbon dioxide contains carbon-14.<ref>{{cite book |last1=Aitken |first1=M.J. |title=Science-based Dating in Archaeology |date=1990 |isbn=978-0-582-49309-4 |pages=56–58|publisher=Longman }}</ref>

Carbon-rich asteroids are relatively preponderant in the outer parts of the [[asteroid belt]] in the Solar System. These asteroids have not yet been directly sampled by scientists. The asteroids can be used in hypothetical [[asteroid mining|space-based carbon mining]], which may be possible in the future, but is currently technologically impossible.<ref>{{cite web |last1=Nichols |first1=Charles R. |title=Voltatile Products from Carbonaceous Asteroids |url=http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources21.pdf |website=UAPress.Arizona.edu |access-date=12 November 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160702023807/http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources21.pdf |archive-date=2 July 2016 |df=dmy-all}}</ref>