Editing Carbon (section)

==Characteristics==
[[File:Carbon-phase-diagramp.svg|thumb|left|upright=1.3|Theoretically predicted phase diagram of carbon, from 1989. Newer work indicates that the melting point of diamond (top-right curve) does not go above about 9000&nbsp;K.<ref name="Eggert-2009">{{cite journal |display-authors=etal |last1=J.H. Eggert |title=Melting temperature of diamond at ultrahigh pressure |journal=Nature Physics |date=Nov 8, 2009 |volume=6 |issue=1 |pages=40–43 |doi=10.1038/nphys1438 |doi-access=free|bibcode=2010NatPh...6...40E }}</ref>]]
The [[allotropes of carbon]] include [[graphite]], one of the softest known substances, and [[diamond]], the hardest naturally occurring substance. It [[Chemical bond|bonds]] readily with other small atoms, including other carbon atoms, and is capable of forming multiple stable [[covalent]] bonds with suitable multivalent atoms. Carbon is a component element in the large majority of all [[chemical compound]]s, with about two hundred million examples having been described in the published chemical literature.<ref name="ChemAbs-2023"/> Carbon also has the highest [[sublimation (phase transition)|sublimation]] point of all elements. At [[atmospheric pressure]] it has no melting point, as its [[triple point]] is at {{convert|10.8|±|0.2|MPa|atm psi}} and {{convert|4600|±|300|K|C F|-1}},<ref name="triple2" /><ref name="triple3" /> so it sublimes at about {{convert|3900|K|C F}}.<ref name="Greenville Whittaker-1978">{{cite journal |journal=Nature |volume=276 |pages=695–696 |date=1978 |doi=10.1038/276695a0 |title=The controversial carbon solid−liquid−vapour triple point |first=A. |last=Greenville Whittaker |issue=5689 |bibcode=1978Natur.276..695W |s2cid=4362313}}</ref><ref>{{cite news |url=http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf |title=On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam |first=J. M. |last=Zazula |date=1997 |access-date=2009-06-06 |publisher=CERN |url-status=live |archive-url=https://web.archive.org/web/20090325230751/http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf |archive-date=2009-03-25}}</ref> Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised [[pi bond|pi system]] is much more vulnerable to attack. For example, graphite can be oxidised by hot concentrated [[nitric acid]] at standard conditions to [[mellitic acid]], C<sub>6</sub>(CO<sub>2</sub>H)<sub>6</sub>, which preserves the hexagonal units of graphite while breaking up the larger structure.{{sfn|Greenwood|Earnshaw|1997|pages=289-292}}

Carbon is the sixth element, with a ground-state [[electron configuration]] of 1s<sup>2</sup>2s<sup>2</sup>2p<sup>2</sup>, of which the four outer electrons are [[valence electron]]s. Its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7&nbsp;kJ/mol, are much higher than those of the heavier group-14 elements. The electronegativity of carbon is 2.5, significantly higher than the heavier group-14 elements (1.8–1.9), but close to most of the nearby nonmetals, as well as some of the second- and third-row [[transition metal]]s. Carbon's [[covalent radii]] are normally taken as 77.2&nbsp;pm (C−C), 66.7&nbsp;pm (C=C) and 60.3&nbsp;pm (C≡C), although these may vary depending on coordination number and what the carbon is bonded to. In general, covalent radius decreases with lower coordination number and higher bond order.{{sfn|Greenwood|Earnshaw|1997|pages=276-278}}

Carbon-based compounds form the basis of all known life on Earth, and the [[carbon-nitrogen-oxygen cycle]] provides a small portion of the energy produced by the Sun, and most of the energy in larger stars (e.g. [[Sirius]]). Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react with [[sulfuric acid]], [[hydrochloric acid]], [[chlorine]] or any [[Alkali metals|alkalis]]. At elevated temperatures, carbon reacts with oxygen to form [[carbon oxides]] and will rob oxygen from metal oxides to leave the elemental metal. This [[exothermic reaction]] is used in the iron and steel industry to [[smelting|smelt]] iron and to control the carbon content of [[steel]]:{{sfn|Greenwood|Earnshaw|1997|pages=289-301}}
:{{chem|Fe|3|O|4}} + 4 C{{sub|(s)}} + 2 {{chem|O|2}} → 3 Fe{{sub|(s)}} + 4 {{chem|CO|2}}{{sub|(g)}}.

Carbon reacts with sulfur to form [[carbon disulfide]], and it reacts with steam in the coal-gas reaction used in [[coal gasification]]:{{sfn|Greenwood|Earnshaw|1997|pages=290}}<ref>{{cite journal | last=Warnecke | first=Friedrich | title=Die gewerbliche Schwefelkohlenstoffvergiftung | journal=Archiv für Gewerbepathologie und Gewerbehygiene | publisher=Springer Science and Business Media LLC | volume=11 | issue=2 | year=1941 | issn=0340-0131 | doi=10.1007/bf02122927 | pages=198–248 | bibcode=1941IAOEH..11..198W | s2cid=72106188 | language=de}}</ref><ref>{{cite book|title=The chemistry of gas lighting|first=Lewis|last=Thompson|pages=91–98|publisher=Office of "The Journal of Gas Lighting"|date=1850|url=https://books.google.com/books?id=sac_AAAAYAAJ}}</ref>

:C{{sub|(s)}} + H{{sub|2}}O{{sub|(g)}} → CO{{sub|(g)}} + H{{sub|2(g)}}.

Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide [[cementite]] in steel and [[tungsten carbide]], widely used as an abrasive and for making hard tips for cutting tools.{{sfn|Greenwood|Earnshaw|1997|pages=297-300}}<ref name="carbideu">{{cite book |author1=Helmut Tulhoff |author2=Juliane A. Meese-Marktscheffel |author3=Carina Oelgardt |author4=Christian Kind |author5=Markus Weinmann |author6=Tino Säuberlich |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2017 |isbn=9783527306732 |pages=5–11 |language=en |chapter=Carbides |doi=10.1002/14356007.a05_061.pub2}}</ref>

The system of carbon allotropes spans a range of extremes:
{|class="wikitable"
|Graphite is one of the softest materials known.
|style="width: 50%;"|Synthetic [[aggregated diamond nanorod|nanocrystalline diamond]] is the hardest material known.<ref>{{cite journal |last1=Irifune |first1=Tetsuo |last2=Kurio |first2=Ayako |last3=Sakamoto |first3=Shizue |last4=Inoue |first4=Toru |last5=Sumiya |first5=Hitoshi |title=Materials: Ultrahard polycrystalline diamond from graphite |journal=Nature |volume=421 |pages=599–600 |date=2003 |doi=10.1038/421599b |pmid=12571587 |issue=6923 |bibcode=2003Natur.421..599I |s2cid=52856300}}</ref>
|-
|Graphite is a very good lubricant, displaying [[superlubricity]].<ref>{{cite journal |title=Superlubricity of Graphite |url=http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |date=2004 |last1=Dienwiebel |first1=Martin |last2=Verhoeven |first2=Gertjan |last3=Pradeep |first3=Namboodiri |last4=Frenken |first4=Joost |last5=Heimberg |first5=Jennifer |last6=Zandbergen |first6=Henny |journal=Physical Review Letters |volume=92 |issue=12 |pages=126101 |bibcode=2004PhRvL..92l6101D |doi=10.1103/PhysRevLett.92.126101 |pmid=15089689 |s2cid=26811802 |url-status=live |archive-url=https://web.archive.org/web/20110917120623/http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |archive-date=2011-09-17}}</ref>
|Diamond is the ultimate abrasive.
|-
|Graphite is a [[electrical conductor|conductor]] of electricity.<ref>{{cite journal |last1=Deprez |first1=N. |last2=McLachan |first2=D. S. |date=1988 |title=The analysis of the electrical conductivity of graphite conductivity of graphite powders during compaction |journal=[[Journal of Physics D: Applied Physics]] |volume=21 |issue=1 |pages=101–107 |doi=10.1088/0022-3727/21/1/015 |bibcode=1988JPhD...21..101D |s2cid=250886376}}</ref>
|Diamond is an excellent electrical [[insulator (electrical)|insulator]],<ref>{{cite journal |last=Collins |first=A. T. |title=The Optical and Electronic Properties of Semiconducting Diamond |journal=[[Philosophical Transactions of the Royal Society A]] |volume=342 |pages=233–244 |date=1993 |doi=10.1098/rsta.1993.0017 |issue=1664 |bibcode=1993RSPTA.342..233C |s2cid=202574625}}</ref> and has the highest breakdown electric field of any known material.
|-
|Some forms of graphite are used for [[thermal insulation]] (i.e. firebreaks and heat shields), but some [[pyrolytic graphite|other forms]] are good thermal conductors.
|Diamond is the best known naturally occurring [[list of thermal conductivities|thermal conductor]].
|-
|Graphite is [[opaque]].
|Diamond is highly transparent.
|-
|Graphite crystallizes in the [[hexagonal system]].<ref>{{cite book |title=Graphite and Precursors |author=Delhaes, P. |publisher=CRC Press |date=2001 |url=https://books.google.com/books?id=7p2pgNOWPbEC&pg=PA146 |isbn=978-90-5699-228-6}}</ref>
|Diamond crystallizes in the [[cubic system]].
|-
|Amorphous carbon is completely [[isotropic]].
|Carbon nanotubes are among the most [[anisotropic]] materials known.
|}

===Allotropes===
{{Main|Allotropes of carbon}}
[[Atomic carbon]] is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with diverse molecular configurations called [[allotrope]]s. The three relatively well-known allotropes of carbon are [[amorphous carbon]], [[graphite]], and diamond. Once considered exotic, [[fullerene]]s are nowadays commonly synthesized and used in research; they include [[buckyball]]s,<ref name="Unwin-2007"/><ref name="Ebbesen-1997">{{cite book |editor=Ebbesen, T. W. |editor-link=Thomas Ebbesen |date=1997 |title=Carbon nanotubes—preparation and properties |publisher=CRC Press |location=Boca Raton, Florida |isbn=978-0-8493-9602-1}}</ref> [[carbon nanotube]]s,<ref name="Springer-2001">{{cite book |editor=Dresselhaus, M. S. |editor-link1=Mildred Dresselhaus |editor2=Dresselhaus, G. |editor3=Avouris, Ph. |editor-link3=Phaedon Avouris |date=2001 |title=Carbon nanotubes: synthesis, structures, properties and applications |series=Topics in Applied Physics |volume=80 |isbn=978-3-540-41086-7 |location=Berlin |publisher=Springer}}</ref> [[carbon nanobud]]s<ref name="Nasibulin-2007">{{cite journal |date=2007 |title=A novel hybrid carbon material |journal=Nature Nanotechnology |volume=2 |issue=3 |pages=156–161 |doi=10.1038/nnano.2007.37 |pmid=18654245 |s2cid=6447122 |bibcode=2007NatNa...2..156N |doi-access=free |last1=Nasibulin |first1=Albert G. |author-link1=Albert Nasibulin |last2=Pikhitsa |first2=P. V. |last3=Jiang |first3=H. |last4=Brown |first4=D. P. |last5=Krasheninnikov |first5=A. V. |last6=Anisimov |first6=A. S. |last7=Queipo |first7=P. |last8=Moisala |first8=A. |last9=Gonzalez |first9=D. |display-authors=8}}</ref> and [[carbon nanofibers|nanofibers]].<ref>{{cite journal |date=2007 |title=Investigations of NanoBud formation |journal=Chemical Physics Letters |volume=446 |issue=1 |pages=109–114 |doi=10.1016/j.cplett.2007.08.050 |bibcode=2007CPL...446..109N |last1=Nasibulin |first1=A. |last2=Anisimov |first2=Anton S. |last3=Pikhitsa |first3=Peter V. |last4=Jiang |first4=Hua |last5=Brown |first5=David P. |last6=Choi |first6=Mansoo |last7=Kauppinen |first7=Esko I.}}</ref><ref>{{cite journal |date=2004 |title=Synthesis and characterisation of carbon nanofibers with macroscopic shaping formed by catalytic decomposition of C{{sub |2}}H{{sub|6}}/H{{sub|2}} over nickel catalyst |journal=Applied Catalysis A: General|volume=274|issue=1–2|pages=1–8|doi=10.1016/j.apcata.2004.04.008 |author=Vieira, R |last2=Ledoux|first2=Marc-Jacques |last3=Pham-Huu|first3=Cuong}}</ref> Several other exotic allotropes have also been discovered, such as [[lonsdaleite]],<ref name="Frondel-1967">{{cite journal |date=1967 |title=Lonsdaleite, a new hexagonal polymorph of diamond |journal=Nature |volume=214 |pages=587–589 |issue=5088 |bibcode=1967Natur.214..587F |s2cid=4184812 |doi=10.1038/214587a0 |first1=Clifford |last1=Frondel |last2=Marvin |first2=Ursula B. |author-link2=Ursula Marvin}}</ref> [[glassy carbon]],<ref name="Harris-2004"/> [[carbon nanofoam]]<ref>{{cite journal |date=1999 |title=Structural analysis of a carbon foam formed by high pulse-rate laser ablation |journal=Applied Physics A: Materials Science & Processing |volume=69 |pages=S755–S758 |doi=10.1007/s003390051522 |issue=7 |bibcode=1999ApPhA..69S.755R |s2cid=96050247 |author=Rode, A. V. |last2=Hyde |first2=S. T. |last3=Gamaly |first3=E. G. |last4=Elliman |first4=R. G. |last5=McKenzie |first5=D. R. |last6=Bulcock |first6=S.}}</ref> and [[linear acetylenic carbon]] (carbyne).<ref name="Heimann-1999">{{cite book |author=Heimann, Robert Bertram |author2=Evsyukov, Sergey E. |author3=Kavan, Ladislav |name-list-style=amp |title=Carbyne and carbynoid structures |url=https://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |access-date=2011-06-06 |date=28 February 1999 |publisher=Springer |isbn=978-0-7923-5323-2 |pages=1– |url-status=live |archive-url=https://web.archive.org/web/20121123153424/http://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |archive-date=23 November 2012}}</ref>

[[Graphene]] is a two-dimensional sheet of carbon with the atoms arranged in a hexagonal lattice. As of 2009, graphene appears to be the strongest material ever tested.<ref name="Lee-2008">{{cite journal |last1=Lee |first1=C. |last2=Wei |first2=X. |last3=Kysar |first3=J. W. |last4=Hone |first4=J. |date=2008 |title=Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene |journal=Science |volume=321 |issue=5887 |pages=385–8 |bibcode=2008Sci...321..385L |doi=10.1126/science.1157996 |pmid=18635798 |s2cid=206512830}}
* {{cite press release |author=Phil Schewe |date=July 28, 2008 |title=World's Strongest Material |website=Inside Science News Service |url=http://www.aip.org/isns/reports/2008/027.html |archive-url=https://web.archive.org/web/20090531134104/http://www.aip.org/isns/reports/2008/027.html |archive-date=2009-05-31}}</ref> The process of separating it from graphite will require some further technological development before it is economical for industrial processes.<ref name="Sanderson-2008">{{cite web |url=http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |title=Toughest Stuff Known to Man : Discovery Opens Door to Space Elevator |last=Sanderson |first=Bill |date=2008-08-25 |publisher=nypost.com |access-date=2008-10-09 |url-status=live |archive-url=https://web.archive.org/web/20080906171324/http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |archive-date=2008-09-06}}</ref> If successful, graphene could be used in the construction of a [[space elevator]]. It could also be used to safely store hydrogen for use in a hydrogen based engine in cars.<ref>{{cite journal |last1=Jin |first1=Zhong |last2=Lu |first2=Wei |last3=O'Neill |first3=Kevin J. |last4=Parilla |first4=Philip A. |last5=Simpson |first5=Lin J. |last6=Kittrell |first6=Carter |last7=Tour |first7=James M. |date=2011-02-22 |title=Nano-Engineered Spacing in Graphene Sheets for Hydrogen Storage |journal=Chemistry of Materials |volume=23 |issue=4 |pages=923–925 |doi=10.1021/cm1025188 |issn=0897-4756}}</ref>

[[File:Glassy carbon and a 1cm3 graphite cube HP68-79.jpg|thumb|left|A large sample of glassy carbon]] The [[amorphous]] form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such as charcoal, [[lampblack]] (soot), and [[activated carbon]]. At normal pressures, carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused [[hexagon]]al rings, just like those in [[aromatic hydrocarbon]]s.<ref>{{cite book |title=The polymorphism of elements and compounds |last=Jenkins |first=Edgar |date=1973 |publisher=Taylor & Francis |isbn=978-0-423-87500-3 |page=30 |url=https://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |access-date=2011-05-01 |url-status=live |archive-url=https://web.archive.org/web/20121123204229/http://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |archive-date=2012-11-23}}</ref> The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak [[van der Waals force]]s.<!-- no evidence for upper case van der Waals; see [[Talk:Van der Waals#Van should be capitalized unless preceded by first name]] rebuttal --> This gives graphite its softness and its [[cleavage (crystal)|cleaving]] properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a [[delocalized electron|π-cloud]], graphite conducts [[electricity]], but only in the plane of each [[covalently bonded]] sheet. This results in a lower bulk [[electrical conductivity]] for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.{{sfn|Greenwood|Earnshaw|1997|pages=274-278}}

[[File:Eight Allotropes of Carbon.svg|thumb|upright=1.35|Some allotropes of carbon: a) [[diamond]]; b) [[graphite]]; c) [[lonsdaleite]]; d–f) [[fullerene]]s (C{{sub|60}}, C{{sub|540}}, C{{sub|70}}); g) [[amorphous carbon]]; h) [[carbon nanotube]]]]

At very high pressures, carbon forms the more compact allotrope, diamond, having nearly twice the density of graphite. Here, each atom is bonded [[tetrahedron|tetrahedrally]] to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same [[cubic structure]] as [[silicon]] and [[germanium]], and because of the strength of the carbon-carbon [[chemical bond|bonds]], it is the hardest naturally occurring substance measured by [[Mohs scale|resistance to scratching]]. Contrary to the popular belief that ''"diamonds are forever"'', they are thermodynamically unstable ([[Standard Gibbs free energy of formation|Δ<sub>f</sub>''G''°]](diamond, 298&nbsp;K) = 2.9&nbsp;kJ/mol<ref>{{cite journal |last1=Rossini |first1=F. D. |last2=Jessup |first2=R. S. |date=1938 |title=Heat and Free Energy of Formation of Carbon Dioxide and of the Transition Between Graphite and Diamond |journal=Journal of Research of the National Bureau of Standards |volume=21 |issue=4 |pages=491 |doi=10.6028/jres.021.028 |doi-access=free}}</ref>) under normal conditions (298&nbsp;K, 10<sup>5</sup>&nbsp;Pa) and should theoretically transform into graphite.<ref name="World of Carbon">{{cite web |url=http://invsee.asu.edu/nmodules/Carbonmod/point.html |archive-url=https://web.archive.org/web/20010531203728/http://invsee.asu.edu/nmodules/Carbonmod/point.html |url-status=dead |archive-date=2001-05-31 |title=World of Carbon&nbsp;– Interactive Nano-visulisation in Science & Engineering Education (IN-VSEE) |access-date=2008-10-09}}</ref> But due to a high [[activation energy]] barrier, the transition into graphite is so slow at normal temperature that it is unnoticeable. However, at very high temperatures diamond will turn into graphite, and diamonds can burn up in a house fire. The bottom left corner of the phase diagram for carbon has not been scrutinized experimentally. Although a computational study employing [[density functional theory]] methods reached the conclusion that as {{nowrap|''T'' → 0 K}} and {{nowrap|''p'' → 0 Pa}}, diamond becomes more stable than graphite by approximately 1.1&nbsp;kJ/mol,<ref>{{cite journal |last=Grochala |first=Wojciech |date=2014-04-01 |title=Diamond: Electronic Ground State of Carbon at Temperatures Approaching 0 K |journal=Angewandte Chemie International Edition |language=en |volume=53 |issue=14 |pages=3680–3683 |doi=10.1002/anie.201400131 |pmid=24615828 |issn=1521-3773 |s2cid=13359849}}</ref> more recent and definitive experimental and computational studies show that graphite is more stable than diamond for {{nowrap|''T'' < 400 K}}, without applied pressure, by 2.7&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;0&nbsp;K and 3.2&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;298.15&nbsp;K.<ref>{{cite journal |first1=Mary Anne |last1=White |author-link1=Mary Anne White |first2=Samer |last2=Kahwaji |first3=Vera L. S. |last3=Freitas |first4=Riko |last4=Siewert |first5=Joseph A. |last5=Weatherby |first6=Maria D. M. C. |last6=Ribeiro da Silva |first7=Sergey P. |last7=Verevkin |first8=Erin R. |last8=Johnson |first9=Josef W. |last9=Zwanziger |date=2021 |title=The Relative Thermal Stability of Diamond and Graphite |journal=Angewandte Chemie International Edition |language=en |volume=60 |issue=3 |pages=1546–1549 |doi=10.1002/anie.202009897 |issn=1433-7851 |pmid=32970365 |s2cid=221888151}}</ref> Under some conditions, carbon crystallizes as [[lonsdaleite]], a [[hexagonal crystal family|hexagonal crystal lattice]] with all atoms covalently bonded and properties similar to those of diamond.<ref name="Frondel-1967"/>

[[Fullerene]]s are a synthetic crystalline formation with a graphite-like structure, but in place of flat [[hexagonal crystal system|hexagonal cells]] only, some of the cells of which fullerenes are formed may be pentagons, nonplanar hexagons, or even heptagons of carbon atoms. The sheets are thus warped into spheres, ellipses, or cylinders. The properties of fullerenes (split into buckyballs, buckytubes, and nanobuds) have not yet been fully analyzed and represent an intense area of research in [[nanomaterial]]s. The names ''fullerene'' and ''buckyball'' are given after [[Richard Buckminster Fuller]], popularizer of [[geodesic dome]]s, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming [[spheroid]]s (the best-known and simplest is the soccerball-shaped C{{sub|60}} [[buckminsterfullerene]]).<ref name="Unwin-2007"/> Carbon nanotubes (buckytubes) are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow [[cylinder]].<ref name="Ebbesen-1997"/><ref name="Springer-2001"/> Nanobuds were first reported in 2007 and are hybrid buckytube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure.<ref name="Nasibulin-2007"/>

[[File:C2014_Q2.jpg|thumb|Comet [[C/2014 Q2 (Lovejoy)]] surrounded by glowing carbon vapor]]
Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2&nbsp;kg/m{{sup|3}}.<ref>{{cite journal |url=http://www.aip.org/pnu/2004/split/678-1.html |title=Carbon Nanofoam is the World's First Pure Carbon Magnet |journal=Physics News Update |url-status=live |volume=678 |issue=1 |date=March 26, 2004 |author=Schewe, Phil |author2=Stein, Ben |name-list-style=amp |archive-url=https://web.archive.org/web/20120307104655/http://www.aip.org/pnu/2004/split/678-1.html |archive-date=March 7, 2012}}</ref> Similarly, [[glassy carbon]] contains a high proportion of closed [[porosity]],<ref name="Harris-2004"/> but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. [[Linear acetylenic carbon]]<ref name="Heimann-1999"/> has the chemical structure<ref name="Heimann-1999"/> −(C≡C){{sub|{{mvar|n}}}}−&nbsp;. Carbon in this modification is linear with ''sp'' [[orbital hybridization]], and is a [[polymer]] with alternating single and triple bonds. This carbyne is of considerable interest to [[nanotechnology]] as its [[Young's modulus]] is 40&nbsp;times that of the hardest known material&nbsp;– diamond.<ref>{{cite journal |last1=Itzhaki |first1=Lior |last2=Altus |first2=Eli |last3=Basch |first3=Harold |last4=Hoz |first4=Shmaryahu |year=2005 |title=Harder than diamond: Determining the cross-sectional area and Young's modulus of molecular rods |journal=Angew. Chem. Int. Ed. |volume=44 |issue=45 |pages=7432–7435 |pmid=16240306 |doi=10.1002/anie.200502448}}</ref>

In 2015, a team at the [[North Carolina State University]] announced the development of another allotrope they have dubbed [[Q-carbon]], created by a high-energy low-duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, [[fluorescence]], and a hardness superior to diamonds.<ref>{{cite press release |title=Researchers find new phase of carbon, make diamond at room temperature |date=2015-11-30 |website=news.ncsu.edu |url=https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |access-date=2016-04-06 |url-status=live |archive-url=https://web.archive.org/web/20160406002158/https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |archive-date=2016-04-06}}</ref>

In the vapor phase, some of the carbon is in the form of highly reactive [[diatomic carbon]] dicarbon ({{chem2|C2}}). When excited, this gas glows green.<ref>{{cite journal | title = Chemistry of the singlet and triplet C<sub>2</sub> molecules. Mechanism of acetylene formation from reaction with acetone and acetaldehyde | first1 = Philip S. | last1 = Skell | author-link = Philip Skell | first2 = James H. | last2 = Plonka | journal = [[Journal of the American Chemical Society]] | year = 1970 | volume = 92 | issue = 19 | pages = 5620–5624| doi = 10.1021/ja00722a014| bibcode = 1970JAChS..92.5620S }}</ref><ref>{{cite journal |author1=J. Borsovszky |author2=K. Nauta |author3=J. Jiang |author4=C.S. Hansen |author5=L.K. McKemmish |author6=R.W. Field |author7=J.F. Stanton |author8=S.H. Kable |author9=T.W. Schmidt |title=Photodissociation of dicarbon: How nature breaks an unusual multiple bond |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2021 |volume=118 |issue=52 |page=e2113315118 |doi=10.1073/pnas.2113315118 |doi-access=free |pmid=34930845 |pmc=8719853 |bibcode=2021PNAS..11813315B |language=en}}</ref>

===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>

===Isotopes===
{{Main|Isotopes of carbon}}
[[Isotope]]s of carbon are [[atomic nuclei]] that contain six [[proton]]s plus a number of [[neutron]]s (varying from 2 to 16). Carbon has two stable, naturally occurring isotopes.<ref name="WebElements">{{cite web |url=http://www.webelements.com/webelements/elements/text/C/isot.html |title=Carbon&nbsp;– Naturally occurring isotopes |publisher=WebElements Periodic Table |access-date=2008-10-09 |url-status=live |archive-url=https://web.archive.org/web/20080908030327/http://www.webelements.com/webelements/elements/text/C/isot.html |archive-date=2008-09-08}}</ref> The isotope [[carbon-12]] ({{sup|12}}C) forms 98.93% of the carbon on Earth, while [[carbon-13]] ({{sup|13}}C) forms the remaining 1.07%.<ref name="WebElements" /> The concentration of {{sup|12}}C is further increased in biological materials because biochemical reactions discriminate against {{sup|13}}C.<ref>{{cite journal |last1=Gannes |first1=Leonard Z. |last2=Del Rio |first2=Carlos Martı́nez |last3=Koch |first3=Paul |title=Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology |journal=Comparative Biochemistry and Physiology&nbsp;– Part A: Molecular & Integrative Physiology |volume=119 |issue=3 |pages=725–737 |date=1998 |doi=10.1016/S1095-6433(98)01016-2 |pmid=9683412}}</ref> In 1961, the [[International Union of Pure and Applied Chemistry]] (IUPAC) adopted the isotope carbon-12 as the basis for [[atomic weight]]s.<ref>{{cite web |url=http://www.bipm.org/en/si/base_units/ |title=Official SI Unit definitions |access-date=2007-12-21 |url-status=live |archive-url=https://web.archive.org/web/20071014094602/http://www.bipm.org/en/si/base_units/ |archive-date=2007-10-14}}</ref> Identification of carbon in [[nuclear magnetic resonance]] (NMR) experiments is done with the isotope {{sup|13}}C.

[[Carbon-14]] ({{sup|14}}C) is a naturally occurring [[radioisotope]], created in the [[upper atmosphere]] (lower [[stratosphere]] and upper [[troposphere]]) by interaction of nitrogen with cosmic rays.<ref>{{cite book |first=S. |last=Bowman |date=1990 |title=Interpreting the past: Radiocarbon dating |publisher=British Museum Press |isbn=978-0-7141-2047-8}}</ref> It is found in trace amounts on Earth of 1 part per [[10^12|trillion]] (0.0000000001%) or more, mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials.<ref>{{cite web |last=Brown |first=Tom |date=March 1, 2006 |url=http://www.llnl.gov/str/March06/Brown.html |title=Carbon Goes Full Circle in the Amazon |publisher=Lawrence Livermore National Laboratory |access-date=2007-11-25 |url-status=live |archive-url=https://web.archive.org/web/20080922031202/https://www.llnl.gov/str/March06/Brown.html |archive-date=September 22, 2008}}</ref> This isotope decays by 0.158&nbsp;MeV [[beta decay|β{{sup|−}} emission]]. Because of its relatively short [[half-life]] of {{val|5700|30}}&nbsp;years,{{NUBASE2020|name}} {{sup|14}}C is virtually absent in ancient rocks. The amount of {{sup|14}}C in the [[atmosphere]] and in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used in [[radiocarbon dating]], invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000&nbsp;years.<ref>{{cite book |last=Libby |first=W. F. |date=1952 |title=Radiocarbon dating |publisher=Chicago University Press and references therein}}</ref><ref>{{cite web |last=Westgren |first=A. |date=1960 |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html |title=The Nobel Prize in Chemistry 1960 |publisher=Nobel Foundation |access-date=2007-11-25 |url-status=live |archive-url=https://web.archive.org/web/20071025003508/http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html |archive-date=2007-10-25}}</ref>

There are 15 known isotopes of carbon and the shortest-lived of these is {{sup|8}}C which decays through [[proton emission]] and has a half-life of 3.5{{e|−21}} s.{{NUBASE2020|ref}} The exotic {{sup|19}}C exhibits a [[nuclear halo]], which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density.<ref>{{cite journal |title=Beaming Into the Dark Corners of the Nuclear Kitchen |last1=Watson |first1=A. |journal=Science |volume=286 |issue=5437 |pages=28–31 |date=1999 |s2cid=117737493 |doi=10.1126/science.286.5437.28}}</ref>

===Formation in stars===
{{Main|Triple-alpha process|CNO cycle}}
Formation of the carbon atomic nucleus occurs within a [[giant star|giant]] or [[supergiant]] star through the [[triple-alpha process]]. This requires a nearly simultaneous collision of three [[alpha particle]]s (helium nuclei), as the products of further [[nuclear fusion]] reactions of helium with hydrogen or another helium nucleus produce [[isotopes of lithium|lithium-5]] and [[isotopes of beryllium|beryllium-8]] respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei.<ref name="Audi-1997">{{NUBASE 1997}}</ref> The triple-alpha process happens in conditions of temperatures over 100 megakelvins and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang.<ref>{{cite book|last1=Wilson|first1=Robert|title=Astronomy through the ages the story of the human attempt to understand the universe|date=1997|publisher=[[Taylor & Francis]]|location=Basingstoke|isbn=9780203212738|chapter=Chapter 11: The Stars – their Birth, Life, and Death}}</ref>

According to current physical cosmology theory, carbon is formed in the interiors of stars on the [[horizontal branch]].<ref name="Ostlie-2007">{{cite book |last1=Ostlie |first1=Dale A. |last2=Carroll |first2=Bradley W. |name-list-style=amp |title=An Introduction to Modern Stellar Astrophysics |publisher=Addison Wesley |location=San Francisco (CA) |date=2007 |isbn=978-0-8053-0348-3}}</ref> When massive stars die as supernova, the carbon is scattered into space as dust. This dust becomes component material for the formation of the next-generation star systems with accreted planets.<ref name="Hoover-2014"/><ref>{{cite book |last=Whittet |first=Douglas C. B. |date=2003 |title=Dust in the Galactic Environment |pages=45–46 |publisher=[[CRC Press]] |isbn=978-0-7503-0624-9}}</ref> The Solar System is one such star system with an abundance of carbon, enabling the existence of life as we know it. It is the opinion of most scholars that all the carbon in the Solar System and the [[Milky Way]] comes from dying stars.<ref name="Bohan-2016">{{cite book |last1=Bohan |first1=Elise |url=https://www.worldcat.org/oclc/940282526 |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |pages=10–11, 45, 55, 58–59, 63, 65–71, 75, 78–81, 98, 100, 102 |oclc=940282526 |author-link6=Rebecca Wragg Sykes |author-link7=Peter Chrisp}}</ref><ref>{{cite web |date=May 2003 |title=Is my body really made up of star stuff? |url=https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question57.html |access-date=2023-03-17 |publisher=[[NASA]]}}</ref><ref>{{cite web |last=Firaque |first=Kabir |date=2020-07-10 |title=Explained: How stars provided the carbon that makes life possible |url=https://indianexpress.com/article/explained/explained-how-the-stars-provided-the-carbon-that-makes-life-possible-6499596/ |access-date=2023-03-17 |website=[[The Indian Express]] |language=en}}</ref>

The [[CNO cycle]] is an additional hydrogen fusion mechanism that powers stars, wherein carbon operates as a catalyst.

Rotational transitions of various isotopic forms of carbon monoxide (for example, {{sup|12}}CO, {{sup|13}}CO, and {{sup|18}}CO) are detectable in the [[submillimeter]] wavelength range, and are used in the study of newly forming stars in [[molecular cloud]]s.<ref>{{cite book |last=Pikelʹner |first=Solomon Borisovich |title=Star Formation |url=https://books.google.com/books?id=qbGLgcxnfpIC&pg=PA38 |access-date=2011-06-06 |date=1977 |publisher=Springer |isbn=978-90-277-0796-3 |pages=38 |url-status=live |archive-url=https://web.archive.org/web/20121123220424/http://books.google.com/books?id=qbGLgcxnfpIC&pg=PA38 |archive-date=2012-11-23}}</ref>

===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>