Unlike tooth enamel, soft tissues are constantly being made and remade during life.Thus, their radiocarbon levels mirror those in the changing environment.The researchers found that if they assumed tooth enamel radiocarbon content to be determined by the atmospheric level at the time the tooth was formed, then they could deduce the year of birth.They found that for teeth formed after 1965, enamel radiocarbon content predicted year of birth within 1.5 years.The new method is based on the fact that over the past 60 years, environmental levels of radiocarbon have been significantly perturbed by mid-20th-century episodes of above-ground nuclear weapons testing.Before the nuclear age, the amount of radiocarbon in the environment varied little in the span of a century.To determine year of birth, the researchers focused on tooth enamel.Adult teeth are formed at known intervals during childhood.
Therefore, the radiocarbon level in those tissues post-mortem would indicate the year of death.
In contrast, from 1955 to 1963, atmospheric radiocarbon levels almost doubled.
Since then they have been dropping back toward natural levels.
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