Diferencia entre revisiones de «Ciclo del carbono profundo»

Principalmente, el [[carbono]] entra al [[Manto terrestre|manto]] en forma de [[sedimento]]s ricos en [[carbonato]] a través de la [[tectónica de placas]] propia de la [[corteza oceánica]], que lleva el carbono hacia dentro del manto mediante [[subducción]]. Se conoce poco sobre su [[Convección del manto|circulación dentro del manto]] profundo de la Tierra, pero varios estudios han procurado mejorar la comprensión de su movimiento y sus compuestos en dicha región. Por ejemplo, un estudio de 2011 demostró que el [[ciclo del carbono]] se extiende bien hasta el [[manto inferior]]. El estudio se basó en el análisis de los raros [[diamantes]] superprofundos en un sitio de [[Mato Grosso|Juína, Mato Grosso]], [[Brasil]], que determinó que la composición bruta de algunas [[Inclusión (mineralogía)|inclusiones]] diamantíferas se correspondían con las esperadas para la [[Fusión (cambio de estado)|fusión]] y [[cristalización]] del [[basalto]] en condiciones de presión y temperatura como las reinantes en el manto inferior.<ref>{{Cite news |last1=American Association for the Advancement of Science |url=https://www.sciencedaily.com/releases/2011/09/110915141227.htm |title=Carbon cycle reaches Earth's lower mantle: Evidence of carbon cycle found in 'superdeep' diamonds From Brazil |publisher=ScienceDaily |date=15 Septemberde septiembre de 2011 |access-date=6 de febrero de 2019-02-06}}</ref>

Thus, the investigation's findings indicate that pieces of basaltic oceanic lithosphere act as the principal transport mechanism for carbon to Earth's deep interior. These subducted carbonates can interact with lower mantle [[silicate]]s and metals, eventually forming super-deep diamonds like the one found.<ref>{{cite journal |last1=Stagno |first1=V. |last2=Frost |first2=D. J. |last3=McCammon |first3=C. A. |last4=Mohseni |first4=H. |last5=Fei |first5=Y. |title=The oxygen fugacity at which graphite or diamond forms from carbonate-bearing melts in eclogitic rocks |journal=Contributions to Mineralogy and Petrology |date=5 Februaryde febrero de 2015 |volume=169 |issue=2 |pages=16 |doi=10.1007/s00410-015-1111-1 |bibcode=2015CoMP..169...16S }}</ref>

Carbonates descending to the lower mantle form other compounds besides diamonds. In 2011, carbonates were subjected to an environment similar to that of 1800&nbsp;km deep into the Earth, well within the lower mantle. Doing so resulted in the formations of [[magnesite]], [[siderite]], and numerous varieties of [[graphite]].<ref name="Fiquet 5184–5187">{{Cite journal|last=Fiquet|first=Guillaume|last2=Guyot|first2=François|last3=Perrillat|first3=Jean-Philippe|last4=Auzende|first4=Anne-Line|last5=Antonangeli|first5=Daniele|last6=Corgne|first6=Alexandre|last7=Gloter|first7=Alexandre|last8=Boulard|first8=Eglantine|date=2011-03-29 de marzo de 2011|title=New host for carbon in the deep Earth |journal=Proceedings of the National Academy of Sciences|volume=108|issue=13|pages=5184–5187|doi=10.1073/pnas.1016934108 |pmid=21402927|pmc=3069163|bibcode=2011PNAS..108.5184B}}</ref> Other experiments—as well as [[Petrology|petrologic]] observations—support this claim, finding that magnesite is actually the most stable carbonate phase in the majority of the mantle. This is largely a result of its higher melting temperature.<ref>{{Cite journal|last=Dorfman|first=Susannah M.|last2=Badro|first2=James|last3=Nabiei|first3=Farhang|last4=Prakapenka|first4=Vitali B.|last5=Cantoni|first5=Marco|last6=Gillet|first6=Philippe|date=1 de mayo de 2018-05-01|title=Carbonate stability in the reduced lower mantle |journal=Earth and Planetary Science Letters|volume=489|pages=84–91|doi=10.1016/j.epsl.2018.02.035 |bibcode=2018E&PSL.489...84D}}</ref> Consequently, scientists have concluded that carbonates undergo [[Reduction (chemistry)|reduction]] as they descend into the mantle before being stabilised at depth by low oxygen [[fugacity]] environments. Magnesium, iron, and other metallic compounds act as buffers throughout the process.<ref>{{Cite journal|last=Kelley|first=Katherine A.|last2=Cottrell|first2=Elizabeth|date=2013-06-14 de junio de 2013|title=Redox Heterogeneity in Mid-Ocean Ridge Basalts as a Function of Mantle Source |journal=Science|volume=340|issue=6138|pages=1314–1317|doi=10.1126/science.1233299 |pmid=23641060|bibcode=2013Sci...340.1314C}}</ref> The presence of reduced, elemental forms of carbon like graphite would indicate that carbon compounds are reduced as they descend into the mantle.

Nonetheless, [[Polymorphism (materials science)|polymorphism]] alters carbonate compounds' stability at different depths within the Earth. To illustrate, laboratory simulations and [[density functional theory]] calculations suggest that [[Tetrahedral molecular geometry|tetrahedrally-coordinated]] carbonates are most stable at depths approaching the [[core–mantle boundary]].<ref>{{cite book |doi=10.1016/B978-0-12-811301-1.00002-2 |chapter=Carbon-Bearing Magmas in the Earth's Deep Interior |title=Magmas Under Pressure |pages=43–82 |year=2018 |last1=Litasov |first1=Konstantin D. |last2=Shatskiy |first2=Anton |isbn=978-0-12-811301-1 }}</ref><ref name="Fiquet 5184–5187"/> A 2015 study indicates that the lower mantle's high pressures cause carbon bonds to transition from sp₂ to sp₃ [[Orbital hybridisation|hybridised orbitals]], resulting in carbon tetrahedrally bonding to oxygen.<ref>{{Cite journal|last=Mao|first=Wendy L.|last2=Liu|first2=Zhenxian|last3=Galli|first3=Giulia|last4=Pan|first4=Ding|last5=Boulard|first5=Eglantine|date=2015-02-18 de febrero de 2015|title=Tetrahedrally coordinated carbonates in Earth's lower mantle |journal=Nature Communications|volume=6|pages=6311|doi=10.1038/ncomms7311 |pmid=25692448|bibcode=2015NatCo...6.6311B|arxiv=1503.03538}}</ref> CO₃ trigonal groups cannot form polymerisable networks, while tetrahedral CO₄ can, signifying an increase in carbon's [[coordination number]], and therefore drastic changes in carbonate compounds' properties in the lower mantle. As an example, preliminary theoretical studies suggest that high pressures cause carbonate melt viscosity to increase; the melts' lower mobility as a result of the property changes described is evidence for large deposits of carbon deep into the mantle.<ref>{{Cite journal|last=Carmody|first=Laura|last2=Genge|first2=Matthew|last3=Jones|first3=Adrian P.|date=1 de enero de 2013-01-01|title=Carbonate Melts and Carbonatites |journal=Reviews in Mineralogy and Geochemistry|volume=75|issue=1|pages=289–322|doi=10.2138/rmg.2013.75.10 |bibcode=2013RvMG...75..289J}}</ref>

Accordingly, carbon can remain in the lower mantle for long periods of time, but large concentrations of carbon frequently find their way back to the lithosphere. This process, called carbon outgassing, is the result of carbonated mantle undergoing decompression melting, as well as [[mantle plume]]s carrying carbon compounds up towards the crust.<ref>{{Cite journal|last=Dasgupta|first=Rajdeep|last2=Hirschmann|first2=Marc M.|date=2010-09-15 de septiembre de 2010|title=The deep carbon cycle and melting in Earth's interior |journal=Earth and Planetary Science Letters|volume=298|issue=1|pages=1–13|doi=10.1016/j.epsl.2010.06.039 |bibcode=2010E&PSL.298....1D}}</ref> Carbon is oxidised upon its ascent towards volcanic hotspots, where it is then released as CO₂. This occurs so that the carbon atom matches the oxidation state of the basalts erupting in such areas.<ref>{{cite journal |last1=Frost |first1=Daniel J. |last2=McCammon |first2=Catherine A. |title=The Redox State of Earth's Mantle |journal=Annual Review of Earth and Planetary Sciences |date=May 2008 |volume=36 |issue=1 |pages=389–420 |doi=10.1146/annurev.earth.36.031207.124322|bibcode=2008AREPS..36..389F }}</ref> -->