In nature, carbon exists as three isotopes, two stable, nonradioactive: carbon-12 (12 C), and carbon-13 (13 C), and radioactive carbon-14 (14 C), also known as "radiocarbon".The half-life of 14 C (the time it takes for half of a given amount of 14 C to decay) is about 5,730 years, so its concentration in the atmosphere might be expected to decrease over thousands of years, but 14