Editing Carbon-14 (section)

===In fossil fuels===

{{main|Suess effect}}

Many human-made chemicals are derived from [[fossil fuel]]s (such as [[petroleum]] or [[coal]]) in which {{sup|14}}C is greatly depleted because the age of fossils far exceeds the half-life of {{sup|14}}C. The relative absence of {{chem|14|CO|2}} is therefore used to determine the relative contribution (or [[mixing ratio]]) of fossil fuel oxidation to the total [[carbon dioxide]] in a given region of Earth's [[atmosphere]].<ref name="NOAA-2015">{{cite web
 | url = http://www.esrl.noaa.gov/gmd/outreach/isotopes/c14tracer.html
 | title = The Basics: 14C and Fossil Fuels
 | website = NOAA ESRL GMD Education and Outreach
 | archive-url = https://web.archive.org/web/20150925082306/http://esrl.noaa.gov/gmd/outreach/isotopes/c14tracer.html
 | archive-date = 25 September 2015
 | access-date = 9 Dec 2015
 | quote = All other atmospheric carbon dioxide comes from young sources–namely land-use changes (for example, cutting down a forest in order to create a farm) and exchange with the ocean and terrestrial biosphere. This makes 14C an ideal tracer of carbon dioxide coming from the combustion of fossil fuels. Scientists can use 14C measurements to determine the age of carbon dioxide collected in air samples, and from this can calculate what proportion of the carbon dioxide in the sample comes from fossil fuels.
}}</ref>

Dating a specific sample of fossilized carbonaceous material is more complicated. Such deposits often contain trace amounts of {{sup|14}}C. These amounts can vary significantly between samples, ranging up to 1% of the ratio found in living organisms (an apparent age of about 40,000 years).<ref>{{cite journal|title=Problems associated with the use of coal as a source of C14-free background material| vauthors = Lowe D |journal=Radiocarbon|year=1989|volume=31|issue=2|pages=117–120|url=https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/1127/1132|url-status=live|archive-url=https://web.archive.org/web/20130724153305/https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/1127/1132|archive-date=2013-07-24|doi=10.1017/S0033822200044775|doi-access=free| bibcode = 1989Radcb..31..117L }}</ref> This may indicate contamination by small amounts of bacteria, underground sources of radiation causing a {{sup|14}}N(n,p){{sup|14}}C reaction, direct [[uranium]] decay (though reported measured ratios of {{sup|14}}C/U in uranium-bearing ores<ref>{{cite journal |title=Carbon-14 Abundances in Uranium Ores and Possible Spontaneous Exotic Emission from U-Series Nuclides | vauthors = Jull AJ, Barker D, Donahue DJ |journal=Meteoritics |volume=20 |year=1985 |page=676 |bibcode=1985Metic..20..676J}}</ref> would imply roughly 1 uranium atom for every two carbon atoms in order to cause the {{sup|14}}C/{{sup|12}}C ratio, measured to be on the order of 10{{sup|−15}}), or other unknown secondary sources of {{sup|14}}C production. The presence of {{sup|14}}C in the [[isotopic signature]] of a sample of carbonaceous material possibly indicates its contamination by biogenic sources or the decay of radioactive material in surrounding geologic strata. In connection with building the [[Borexino]] solar neutrino observatory, petroleum feedstock (for synthesizing the primary scintillant) was obtained with low {{sup|14}}C content. In the Borexino Counting Test Facility, a {{sup|14}}C/{{sup|12}}C ratio of 1.94×10{{sup|−18}} was determined;<ref>{{cite journal | vauthors = Alimonti G, Angloher G, Arpesella C, Balata M, Bellini G, Benziger J, Bonetti S, Cadonati L, Calaprice FP, Cecchet G, Chen M | display-authors = 6 |doi = 10.1016/S0370-2693(97)01565-7|title = Measurement of the <sup>14</sup>C abundance in a low-background liquid scintillator |journal = Physics Letters B|volume = 422 |issue=1–4 |year=1998|pages=349–358|bibcode = 1998PhLB..422..349B }}</ref> probable reactions responsible for varied levels of {{sup|14}}C in different [[petroleum reservoir]]s, and the lower {{sup|14}}C levels in methane, have been discussed by Bonvicini et al.<ref>{{cite arXiv|eprint=hep-ex/0308025| vauthors = Bonvicini G, Harris N, Paolone V |title=The chemical history of <sup>14</sup>C in deep oilfields|year=2003}}</ref>