Carbon-14 has a half-life of 5,730 ± 40 years— during the succeeding 5,730 years.
Because carbon-14 decays at this constant rate, an estimate of the date at which an organism died can be made by measuring the amount of its residual radiocarbon.
The researchers found that year-of-death determinations based on nails were accurate to within three years.
Radiocarbon levels in teeth formed before then contained less radiocarbon than expected, so when applied to teeth formed during that period, the method was less precise.To determine year of death, the researchers used radiocarbon levels in soft tissues.To determine year of birth, the researchers focused on tooth enamel.Adult teeth are formed at known intervals during childhood. As soon as a living organism dies, it stops taking in new carbon.
The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. Radiocarbon decays slowly in a living organism, and the amount lost is continually replenished as long as the organism takes in air or food.Once the organism dies, however, it ceases to absorb carbon-14, so that the amount of the radiocarbon in its tissues steadily decreases.In contrast, from 1955 to 1963, atmospheric radiocarbon levels almost doubled.Since then they have been dropping back toward natural levels.However, the researchers suggested that soft tissue radiocarbon content would be transferred to, and preserved in, the pupal cases of insects whose larvae feed on these tissues.