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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.

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.

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.

The discovery of radiocarbon dating probably had a greater influence on modern archaeology than any other technological advance, especially on prehistoric periods where without written records archaeologists could previously only speculate the age of artefacts and sites.

But in a dead organism, no new carbon is coming in, and its carbon 14 gradually begins to decay.Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram.In 1960, he was awarded the Nobel Prize in chemistry for this work.Raw, i.e., uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), "Present" being defined as 1950.Such raw ages can be calibrated to give calendar dates.Since it is chemically indistinguishable from the stable isotopes of carbon (carbon-12 and carbon-13), radiocarbon is taken by plants during photosynthesis and then ingested by animals regularly throughout their lifetimes.