Asked by: Lisa Jago, Reading
Radiocarbon dating is based on the fact that different isotopes (forms) of the element carbon, which is found in all 'organic' materials, can be stable or unstable. When an organism dies, it stops taking up carbon; levels of isotopes C12 and C13 remain constant, but C14 decays, with a half-life of around 5500 years. Thus, if you know the ratio of C14 to C12 and C13 in a sample, you can work out how many times the C14 has halved. If there's a quarter of the original C14, for instance, then two half-lives have passed since the organism died, so it is around 11,000 years old.
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