Carbon 13 dating
See also, on this website, articles on the ages of the geologic periods (Ages), radiometric dating (Radiometric dating), the reliability of radiometric methods (Reliability), a "time machine" for studying the distant past (Time machine) and the "uniformitarian" assumption and how it relates to evolution and the age of the Earth (Uniformitarian).
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Creationists often criticize radiocarbon dating in the context of discussions of the age of the Earth.
But, as is clear even from the very brief discussion in the previous paragraph, radiocarbon dating can say nothing one way or the other about whether the Earth is many millions of years old, since such dates are far beyond this method's range of resolution.
The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.
Organisms capture a certain amount of carbon-14 from the atmosphere when they are alive.
For instance, even in the 1950s, when Willard Libby first developed the process, it was recognized that the scheme assumes that the level of carbon-14 in the atmosphere is constant.
But researchers have known at least since 1969 that the carbon-14 level has not been constant, so that the radiocarbon clock needs to be "calibrated." As a result, various schemes are used to correct and calibrate radiocarbon dates, including: In each case, radiocarbon dates, determined by well-established procedures and calculations, are compared directly with dates determined by the above methods, thus permitting the radiocarbon dates to be accurately calibrated with distinct and independent dating techniques.
Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.The relative width of the red calibration curve indicates the range of uncertainty: In October 2012, a team led by Christopher Ramsey of Oxford University published a new study, based on analyses of varves (alternating light/dark bands in sediments) from Lake Suigetsu, which is located about 350 kilometers west of Tokyo, near the coast of the Sea of Japan.These researchers collected core samples 70 meters deep, and then painstakingly counted the layers, year by year, to obtain a direct record stretching back 52,000 years.For instance, creationist Walt Brown has pointed out inconsistencies in some radiocarbon dates of mammoths -- one part was dated to 40,000 years, another to 26,000 years (and wood surrounding it to 10,000 years), and yet another to between 15,000 and 21,000 years before the present epoch [Brown2001].However, in the scientific results mentioned by Brown, the dates come from different mammoth specimens.