There are three naturally occurring isotopes of carbon: stable 12C and 13C, and unstable radioactive 14C. Radiocarbon dating utilizes the decay of 14C, which is present in very small amounts in all living organisms. The technique involves measuring the ratio of 14C to 12C in a sample and comparing it to the initial ratio when the organism was alive, using a calculated decay rate. This provides a radiocarbon age that then requires calibration against calibration curves to account for past atmospheric variations in 14C levels and obtain an accurate calendar date.