Discovery of carbon dating

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Renfrew (1973) called it 'the radiocarbon revolution' in describing its impact upon the human sciences.Oakley (1979) suggested its development meant an almost complete re-writing of the evolution and cultural emergence of the human species.Libby and his team intially tested the radiocarbon method on samples from prehistoric Egypt.They chose samples whose age could be independently determined.The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14.The reaction is: (Where n is a neutron and p is a proton).Herein lies the true advantage of the radiocarbon method, it is able to be uniformly applied throughout the world.Included below is an impressive list of some of the types of carbonaceous samples that have been commonly radiocarbon dated in the years since the inception of the method: The historical perspective on the development of radiocarbon dating is well outlined in Taylor's (1987) book "Radiocarbon Dating: An archaeological perspective".

Today, there are over 130 radiocarbon dating laboratories around the world producing radiocarbon assays for the scientific community.They exist in equilibrium with the C14 concentration of the atmosphere, that is, the numbers of C14 atoms and non-radioactive carbon atoms stays approximately the same over time.As soon as a plant or animal dies, they cease the metabolic function of carbon uptake; there is no replenishment of radioactive carbon, only decay.By measuring the C14 concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the countrate or number of decay events per gram of Carbon.By comparing this with modern levels of activity (1890 wood corrected for decay to 1950 AD) and using the measured half-life it becomes possible to calculate a date for the death of the sample.

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