Editing Carbon-14 (section)

==Radiocarbon dating==
{{main|Radiocarbon dating}}
Radiocarbon dating is a [[radiometric dating]] method that uses {{sup|14}}C to determine the age of [[carbon]]aceous materials up to about 60,000 years old. The technique was developed by [[Willard Libby]] and his colleagues in 1949<ref>{{cite journal | vauthors = Arnold JR, Libby WF | title = Age determinations by radiocarbon content; checks with samples of known age | journal = Science | volume = 110 | issue = 2869 | pages = 678–680 | date = December 1949 | pmid = 15407879 | doi = 10.1126/science.110.2869.678 | bibcode = 1949Sci...110..678A }}</ref> during his tenure as a professor at the [[University of Chicago]]. Libby estimated that the radioactivity of exchangeable {{sup|14}}C would be about 14 decays per minute (dpm) per gram of carbon, and this is still used as the activity of the ''modern radiocarbon standard''.<ref>{{cite web|url=http://www.c14dating.com/agecalc.html|title=Carbon 14:age calculation|publisher=C14dating.com|access-date=2007-06-11|url-status=live|archive-url=https://web.archive.org/web/20070610195000/http://www.c14dating.com/agecalc.html|archive-date=2007-06-10}}</ref><ref>{{cite web|url=http://www.ldeo.columbia.edu/~martins/isohydro/c_14.html|title=Class notes for Isotope Hydrology EESC W 4886: Radiocarbon <sup>14</sup>C|access-date=2007-06-11|publisher=Martin Stute's homepage at Columbia|url-status=live|archive-url=https://web.archive.org/web/20060924135028/http://www.ldeo.columbia.edu/%7Emartins/isohydro/c_14.html|archive-date=2006-09-24}}</ref> In 1960, Libby was awarded the [[Nobel Prize in chemistry]] for this work.

One of the frequent uses of the technique is to date organic remains from archaeological sites. Plants [[Carbon fixation|fix]] atmospheric carbon during photosynthesis, so the level of {{sup|14}}C in plants and animals when they die, roughly equals the level of {{sup|14}}C in the atmosphere at that time. However, it thereafter decreases exponentially, so the date of death or fixation can be estimated. The initial {{sup|14}}C level for the calculation can either be estimated, or else directly compared with known year-by-year data from tree-ring data ([[dendrochronology]]) up to 10,000 years ago (using overlapping data from live and dead trees in a given area), or else from cave deposits ([[speleothem]]s), back to about 45,000 years before present. A calculation or (more accurately) a direct comparison of carbon-14 levels in a sample, with tree ring or cave-deposit {{sup|14}}C levels of a known age, then gives the wood or animal sample age-since-formation. Radiocarbon is also used to detect disturbance in natural ecosystems; for example, in [[peatland]] landscapes, radiocarbon can indicate that carbon which was previously stored in organic soils is being released due to land clearance or climate change.<ref>{{cite journal | vauthors = Moore S, Evans CD, Page SE, Garnett MH, Jones TG, Freeman C, Hooijer A, Wiltshire AJ, Limin SH, Gauci V | display-authors = 6 | title = Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes | journal = Nature | volume = 493 | issue = 7434 | pages = 660–663 | date = January 2013 | pmid = 23364745 | doi = 10.1038/nature11818 | s2cid = 205232299 | bibcode = 2013Natur.493..660M | url = http://nora.nerc.ac.uk/id/eprint/21405/1/N021405PP.pdf }}</ref><ref>{{Cite journal| vauthors = Dean JF, Garnett MH, Spyrakos E, Billett MF |date=2019|title=The Potential Hidden Age of Dissolved Organic Carbon Exported by Peatland Streams|journal=Journal of Geophysical Research: Biogeosciences|language=en|volume=124|issue=2|pages=328–341|doi=10.1029/2018JG004650|bibcode=2019JGRG..124..328D|issn=2169-8953|doi-access=free|hdl=1893/28684|hdl-access=free}}</ref>

Cosmogenic nuclides are also used as [[Proxy (statistics)|proxy]] data to characterize cosmic particle and solar activity of the distant past.<ref name="Reimer-2020">{{cite journal |journal=Radiocarbon |date=August 2020 | vauthors = Reimer PJ, Austin WE, Bard E, Bayliss A, Blackwell PG, Ramsey CB, Butzin M, Cheng H, Edwards RL, Friedrich M, Grootes PM | display-authors = 6 |title = The INTCAL20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 CAL kBP) |volume=62 |issue=4 |pages=725–757 |doi=10.1017/RDC.2020.41 |doi-access=free |bibcode=2020Radcb..62..725R |hdl=11585/770531 |hdl-access=free }}</ref><ref name="Brehm-2021">{{cite journal | vauthors = Brehm N, Bayliss A, Christl M, Synal HA, Adolphi F, Beer J, Kromer B, Muscheler R, Solanki SK, Usoskin I, Bleicher N | display-authors = 6 |title = Eleven-year solar cycles over the last millennium revealed by radiocarbon in tree rings |journal = Nature Geoscience |volume = 14 |pages = 10–15 |date = 2021 |issue = 1 |doi = 10.1038/s41561-020-00674-0 |bibcode = 2021NatGe..14...10B |s2cid = 230508539 |url = https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A21905 }}</ref>