The basis of radiocarbon dating is simple: all living things absorb carbon from the atmosphere and food sources around them, including a certain amount of natural, radioactive carbon-14. When the plant or animal dies, they stop absorbing, but the radioactive carbon that theyve accumulated continues to decay.

How is carbon-14 formed?

Carbon-14 is continually formed in nature by the interaction of neutrons with nitrogen-14 in the Earths atmosphere; the neutrons required for this reaction are produced by cosmic rays interacting with the atmosphere.