The clock was initially calibrated by dating objects of known age such as Egyptian mummies and bread from Pompeii; work that won Willard Libby the 1960 Nobel Prize in Chemistry.But even he “realized that there probably would be variation”, says Christopher Bronk Ramsey, a geochronologist at the University of Oxford, UK, who led the latest work, published today in Science.The level of atmospheric C is not constant due to human activity, in part because of human combustion of fossil fuels and in part because of above-ground testing of the largely defensive weapon of the thermonuclear bomb.Therefore dates must be calibrated based on Radiometric dating in general, of course, poses a huge problem for people who believe that the universe is 6000-odd years old.Beyond that timespan, the amount of the original C formed by irradiation of nitrogen by neutrons from the spontaneous fission of uranium, present in trace quantities almost everywhere.For these samples, other dating methods must be used.Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.
Many people have been led to believe that radiometric dating methods have proved the earth to be billions of years old.
By measuring the ratio of the radio isotope to non-radioactive carbon, the amount of carbon-14 decay can be worked out, thereby giving an age for the specimen in question.
But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.
Climate records from a Japanese lake are set to improve the accuracy of the dating technique, which could help to shed light on archaeological mysteries such as why Neanderthals became extinct.
Carbon dating is used to work out the age of organic material — in effect, any living thing.