Editing Geologic temperature record (section)

==Methods==
{{Expand section|date=February 2008}}
{{See also|Paleoclimatology|Paleothermometer|Marine isotope stage|Timeline of glaciation}}
Evidence for past temperatures comes mainly from isotopic considerations (especially {{delta|18|O|link}}); the Mg/Ca ratio of [[foramanifera|foram]] tests, and [[alkenone]]s, are also useful. Often, many are used in conjunction to get a multi-proxy estimate for the temperature. This has proven crucial in studies on glacial/interglacial temperature.<ref name="sigmanboyle2000">{{cite journal |title=Glacial/interglacial variations in atmospheric carbon dioxide |journal=Nature |first=D.M. |last=Sigman |author2=E.A. Boyle |volume=407 |issue=6806 |pages=859–869 |date=October 2000 |pmid=11057657 |doi=10.1038/35038000 |bibcode=2000Natur.407..859S |s2cid=7136822 |url=http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120224034604/http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf |archive-date=2012-02-24 }}</ref>