Editing Carbon (section)

===Carbon cycle===
{{Main|Carbon cycle}}
[[File:Carbon cycle-cute diagram.svg|thumb|upright=1.35|Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions tonnes ("GtC" stands for gigatonnes of carbon; figures are {{Circa|2004}}). The purple numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ≈70&nbsp;million GtC of carbonate rock and [[kerogen]].]]

Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it from somewhere and dispose of it somewhere else. The paths of carbon in the environment form the [[carbon cycle]].<ref>Mannion, pp. 51–54.</ref> For example, [[photosynthetic]] plants draw carbon dioxide from the atmosphere (or seawater) and build it into biomass, as in the [[Calvin cycle]], a process of [[carbon fixation]].<ref>Mannion, pp. 84–88.</ref> Some of this biomass is eaten by animals, while some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceans; if bacteria do not consume it, dead plant or animal matter may become petroleum or coal, which releases carbon when burned.<ref>{{cite journal |journal=Science |date=2000 |volume=290 |issue=5490 |pages=291–296 |doi=10.1126/science.290.5490.291 |s2cid=1779934 |bibcode=2000Sci...290..291F |pmid=11030643 |title=The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System |last1=Falkowski |first1=P. |last2=Scholes |first2=R. J. |last3=Boyle |first3=E. |last4=Canadell |first4=J. |last5=Canfield |first5=D. |last6=Elser |first6=J. |last7=Gruber |first7=N. |last8=Hibbard |first8=K. |last9=Högberg |first9=P. |display-authors=8}}</ref><ref>{{cite journal |title=The global terrestrial carbon cycle |date=1993 |last1=Smith |first1=T. M. |last2=Cramer |first2=W. P. |last3=Dixon |first3=R. K. |last4=Leemans |first4=R. |last5=Neilson |first5=R. P. |last6=Solomon |first6=A. M. |journal=Water, Air, & Soil Pollution |volume=70 |issue=1–4 |pages=19–37 |bibcode=1993WASP...70...19S |s2cid=97265068 |doi=10.1007/BF01104986 |url=https://hal-amu.archives-ouvertes.fr/hal-01788303/file/Smith1993.pdf |archive-url=https://web.archive.org/web/20221011170500/https://hal-amu.archives-ouvertes.fr/hal-01788303/file/Smith1993.pdf |archive-date=2022-10-11 |url-status=live}}</ref>