Editing Calcium carbonate (section)

===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.