Editing Coral reef (section)

=== In the geologic past ===
[[File:Ancient coral reefs.jpg|thumb|upright=1.2|right|Ancient coral reefs]]
The times of maximum reef development were in the [[Middle Cambrian]] (513–501 [[Annum|Ma]]), [[Devonian]] (416–359 Ma) and [[Carboniferous]] (359–299 Ma), owing to [[extinction|extinct]] order [[Rugosa]] corals, and [[Late Cretaceous]] (100–66 Ma) and [[Neogene]] (23 Ma–present), owing to [[Order (biology)|order]] [[Scleractinia]] corals.<ref>{{Citation |last=Hallock |first=Pamela |title=Reefs and Reef Limestones in Earth History |date=1997 |work=Life and Death of Coral Reefs |pages=13–42 |place=Boston, MA |publisher=Springer US |doi=10.1007/978-1-4615-5995-5_2 |doi-broken-date=2 November 2024 |isbn=978-0-412-03541-8}}</ref>

Not all reefs in the past were formed by corals: those in the [[Early Cambrian]] (542–513 Ma) resulted from calcareous [[algae]] and [[Archaeocyatha|archaeocyathids]] (small animals with conical shape, probably related to [[sponges]]) and in the [[Late Cretaceous]] (100–66 Ma), when reefs formed by a group of bivalves called [[rudists]] existed; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.<ref name="Johnson_2002" />

Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as ''[[Porites]]'', can indicate changes in [[sea surface temperature]] and sea surface salinity conditions during the growth of the coral. This technique is often used by climate scientists to infer a region's [[paleoclimate]].<ref name="Cobb">{{cite journal |last1=Cobb |first1=K. |last2=Charles |first2=Christopher D. |last3=Cheng |first3=Hai |last4=Edwards |first4=R. Lawrence |year=2003 |title=El Nino/Southern Oscillation and tropical Pacific climate during the past millennium |url=http://eas8001.eas.gatech.edu/papers/Cobb_Nature_2003.pdf |url-status=dead |journal=Nature |volume=424 |issue=6946 |pages=271–276 |bibcode=2003Natur.424..271C |doi=10.1038/nature01779 |pmid=12867972 |archive-url=https://web.archive.org/web/20120111134948/http://eas8001.eas.gatech.edu/papers/Cobb_Nature_2003.pdf |archive-date=January 11, 2012 |s2cid=6088699}}</ref>