Isotope of carbon dating
A very small percentage of carbon, however, consists of the isotope carbon 14, or radiocarbon, which is unstable.Carbon 14 has a half-life of 5,780 years, and is continuously created in Earth's atmosphere through the interaction of nitrogen and gamma rays from outer space.In the case of shellfish, for example, marine shells typically possess a δ13C value between -1 and 4 o/oo (per mille), whereas river shells possess a value of between -8 and -12 o/oo (per mille).
Reported δ13C values from Beta are always the values measured in the IRMS.The extent of isotopic fractionation on the 14C/12C ratio (which must be measured accurately) is approximately double that for the measured 13C/12C ratio.If isotopic fractionation occurs in natural processes, a correction can be made by measuring the ratio of the isotope 13C to the isotope 12C in the sample being dated.Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. 1979, 1986 © Harper Collins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Cite This Source radiocarbon dating A technique for measuring the age of organic remains based on the rate of decay of carbon 14.
Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms. Our Living Language : In the late 1940s, American chemist Willard Libby developed a method for determining when the death of an organism had occurred.Fractionation also describes variations in the isotopic ratios of carbon brought about by non-natural causes.