You probably have seen or read news stories about fascinating ancient artifacts.At an archaeological dig, a piece of wooden tool is unearthed and the archaeologist finds it to be 5,000 years old.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.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.Back in the 1940s, the American chemist Willard Libby used this fact to determine the ages of organisms long dead.Most carbon atoms have six protons and six neutrons in their nuclei and are called carbon 12. But a tiny percentage of carbon is made of carbon 14, or radiocarbon, which has six protons and eight neutrons and is not stable: half of any sample of it decays into other atoms after 5,700 years.
But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock. This is how carbon dating works: Carbon is a naturally abundant element found in the atmosphere, in the earth, in the oceans, and in every living creature.C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14.A form of radiometric dating used to determine the age of organic remains in ancient objects, such as archaeological specimens, on the basis of the half-life of carbon-14 and a comparison between the ratio of carbon-12 to carbon-14 in a sample of the remains to the known ratio in living organisms. A technique for measuring the age of organic remains based on the rate of decay of carbon 14.The carbon 14 present in an organism at the time of its death decays at a steady rate, and so the age of the remains can be calculated from the amount of carbon 14 that is left. The cells of all living things contain carbon atoms that they take in from their environment.