Radiocarbon dating methodology

You read books and find statements that such and such a society or archaeological site is 20,000 years old.

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Kulp lists the assumptions as follows: There are two basic assumptions in the carbon 14 method.One is that the carbon 14 concentration in the carbon dioxide cycle is constant.No one seriously proposes that all the determined dates are without error, but we do not know how many of them are in error—25%? The sharp reduction in previously estimated dates for the close of the glacial period (a date which had been estimated mainly on the basis of counts of varved clays presumably laid down by the retreating ice sheet) has been a source of much argument among Pleistocene geologists as to the relative merits of the varve method (which gave a date of over 20,000 years) and the radiocarbon method (which gave a date of about 11,000 years). Ernst Antevs, has sharply criticized the radiocarbon method, as a result: In appraising C 14 dates, it is essential always to discriminate between the C 14 age and the actual age of the sample.The laboratory analysis determines only the amount of radioactive carbon present …When objects of the Old Kingdom and Middle Kingdom of Egypt yielded carbon dates that appeared roughly comparable with the historical dates, Libby made his method known.

With initial large margin of error and anything that did not square with expectation, judged as “contaminated,” the method appeared to work and was hailed as completely reliablejust as the atomic clock is reliableand this nobody doubted.The most significant problem is that of biological alteration of materials in the soil. To produce an error of 50 percent in the age of a 10,000 year old specimen would require the replacement of more than 25 percent of the carbon atoms.For a 40,000-year-old sample, the figure is only 5 percent, while an error of 5000 years can be produced by about 1 percent of modern materials.However, the laboratory analysis does not determine whether the radioactive carbon is all original or is in part secondary, intrusive, or whether the amount has been altered in still other irregular ways besides by natural decay.7-72 A conference on radiocarbon dating held in October, 1956, resulted in the following conclusions about the reliability of the method: Local variation, especially in shells, can be highly significant.Possible variations in the size of the exchange reservoir under glacial climates are unimportant.The correctness of the method depends greatly on the condition that in the last 40 or 50 thousand years the quantity of water in the hydrosphere (and carbon diluted in it) has not substantially changed. The method depends also on the condition that during the same period of time the influx of cosmic rays or energy particles coming from the stars and the sun has not suffered substantial variations.