Carbon-14 is a radioactive isotope and is present in all living things in a constant amount.Because of the carbon cycle, there is always carbon-14 present in both the air and in living organisms.
Radioactive carbon-14 is continually formed in the atmosphere by the bombardment of cosmic ray neutrons on nitrogen-14 atoms.
After it forms, carbon-14 naturally decomposes, with a half-life of 5,730 years, through beta-particle decay.
Scientists often use the value of 10 half-lives to indicate when a radioactive isotope will be gone, or rather when a very negligible amount is still left.
This is why radiocarbon dating is only useful for dating objects up to around 50,000 years old (about 10 half-lives).
This technique works well for materials up to around 50,000 years old.
Each radioactive isotope decays by a fixed amount, and this amount is called the half-life.
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.
Back in the 1940s, the American chemist Willard Libby used this fact to determine the ages of organisms long dead.