This analysis provides a radiocarbon age of the sample, which must then be calibrated in accordance with a radiocarbon dating calibration curve such as the one pictured below.A variety of factors have caused the amount of 14C present in the atmosphere to vary over time, resulting in deviations between the age predicted by radiocarbon dating and the absolute date of a specimen. Sample contamination must be carefully avoided to ensure measurement accuracy. Cornell University Press, Itha “Dating In Exposed and Surface Contexts”, ed.: Beck, Charlotte. Seminar Press, New York: NY, 1973 “Radiocarbon Dating”. When an organism dies, the intake of 14C ceases, and what was left in the organism begins a measurable disintegration.Carbon-14 has a half-life of 5730 years (±40 years), meaning that (in accordance with the law of radioactive decay) it will take that length of time for half of the carbon present in an organism to decay into stable carbon isotopes."Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure.We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess." [Rasmus Nyerup, (Danish antiquarian), 1802 (in Trigger, 19)].
Libby of the University of Chicago in immediate post-WW2 years.About one carbon nucleus in a trillion contains two extra neutrons, giving a mass of 14.This carbon-14 is radioactive and decays with a half-life of 5730 years.If we have a tree that is 500 years old we can measure the radiocarbon in the 500 rings and see what radiocarbon concentration corresponds to each calendar year.Using very old trees (such as the Bristlecone Pines in the western U. A.), it is possible to make measurements back to a few thousand years ago.