Editing Calcium carbonate (section)

==Geology==
[[File:Rubaksa tufa plug.jpg|thumb|left|Surface precipitation of {{chem2|CaCO3}} as [[tufa]] in [[Rubaksa]], Ethiopia]]
Carbonate is found frequently in geologic settings and constitutes an enormous [[carbon cycle|carbon reservoir]]. Calcium carbonate occurs as [[aragonite]], [[calcite]] and [[dolomite (mineral)|dolomite]] as significant constituents of the [[calcium cycle]]. The [[carbonate mineral]]s form the rock types: [[limestone]], [[chalk]], [[marble]], [[travertine]], [[tufa]], and others.
[[File:Water-of-Five-colored-Pond Huanglong Sichuan China.jpg|thumb|[[Tufa]] at [[Huanglong Scenic and Historic Interest Area|Huanglong]], [[Sichuan]]]]
In warm, clear tropical waters [[coral]]s are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including [[plankton]] (such as [[coccolith]]s and planktic [[foraminifera]]), [[coralline algae]], [[sea sponge|sponges]], [[brachiopod]]s, [[echinoderm]]s, [[bryozoa]] and [[Mollusc shell|mollusks]], are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The [[calcification]] processes are changed by [[ocean acidification]].

Where the [[oceanic crust]] is [[Subduction|subducted]] under a [[continental plate]] sediments will be carried down to warmer zones in the [[asthenosphere]] and [[lithosphere]]. Under these conditions calcium carbonate decomposes to produce [[carbon dioxide]] which, along with other gases, give rise to explosive [[volcano|volcanic eruptions]].

===Carbonate compensation depth===
The [[carbonate compensation depth]] (CCD) is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Increasing pressure also increases the solubility of calcium carbonate. Calcium carbonate is unusual in that its solubility increases with decreasing temperature.<ref name="weyl1959">{{cite journal |last1=Weyl |first1=P.K. |title=The change in solubility of calcium carbonate with temperature and carbon dioxide content |journal=Geochimica et Cosmochimica Acta |date=1959 |volume=17 |issue=3–4 |pages=214–225 |doi=10.1016/0016-7037(59)90096-1|bibcode=1959GeCoA..17..214W}}</ref> The carbonate compensation depth ranges from 4,000 to 6,000 meters below sea level in modern oceans, and the various polymorphs (calcite, aragonite) have different compensation depths based on their stability.<ref>{{Cite book |last=Burton |first=Elizabeth |date=1990 |title=Carbonate compensation depth |chapter=Carbonate carbonatescompensation depthcompensation depth |chapter-url=https://link.springer.com/referenceworkentry/10.1007/1-4020-4496-8_46  |pages=73 |doi=10.1007/1-4020-4496-8_46 |isbn=978-1-4020-4496-0 |via=Elsevier |access-date=22 December 2023 |archive-date=22 December 2023 |archive-url=https://web.archive.org/web/20231222213347/https://link.springer.com/referenceworkentry/10.1007/1-4020-4496-8_46 |url-status=live}}</ref>

===Role in taphonomy===
Calcium carbonate can [[taphonomy|preserve fossils]] through [[permineralization]]. Most of the vertebrate fossils of the [[Two Medicine Formation]]—a [[geologic formation]] known for its [[duck-billed dinosaur]] eggs—are preserved by {{chem2|CaCO3}} permineralization.<ref name="twoturn" /> This type of preservation conserves high levels of detail, even down to the microscopic level. However, it also leaves specimens vulnerable to [[weathering]] when exposed to the surface.<ref name="twoturn">{{cite book |last=Trexler |first=D. |date=2001 |chapter-url=https://books.google.com/books?id=mgc6CS4EUPsC&pg=PA98 |chapter=Two Medicine Formation, Montana: geology and fauna |pages=[https://archive.org/details/mesozoicvertebra0000unse/page/298 298–309] |title=Mesozoic Vertebrate Life |editor1-last=Tanke |editor1-first=D. H. |editor2-last=Carpenter |editor2-first=K. |publisher=Indiana University Press |isbn=978-0-253-33907-2 |url=https://archive.org/details/mesozoicvertebra0000unse/page/298}}</ref>

[[Trilobite]] populations were once thought to have composed the majority of aquatic life during the [[Cambrian]], due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species,<ref>{{Cite book|url=https://www.nap.edu/catalog/11630/out-of-thin-air-dinosaurs-birds-and-earths-ancient-atmosphere|title=Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere|last=Ward|first=Peter|year=2006|isbn=978-0-309-66612-1|language=en|doi=10.17226/11630|access-date=31 December 2017|archive-date=1 January 2018|archive-url=https://web.archive.org/web/20180101030500/https://www.nap.edu/catalog/11630/out-of-thin-air-dinosaurs-birds-and-earths-ancient-atmosphere|url-status=live}}</ref> which had purely [[chitin]]ous shells.