radiocarbon dating

Did You Know? The cells of all living things contain carbon atoms that they take in from their environment. 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. Carbon 12 is very stable. 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. Carbon 14 is continually being created in the Earth's atmosphere by the interaction of nitrogen and gamma rays from outer space. Since atmospheric carbon 14 arises at about the same rate that the atom decays, the Earth's levels of carbon 14 have remained constant. In living organisms, which are always taking in carbon, the levels of carbon 14 likewise stay constant. But in a dead organism, no new carbon is coming in, and its carbon 14 gradually begins to decay. So by measuring carbon 14 levels in an organism that died long ago, researchers can figure out when it died. The procedure of radiocarbon dating can be used for remains that are up to 50,000 years old.