This study examined whether a person's year of birth or year of death could be determined by using precise measurements of carbon-14 levels in different post-mortem tissues.
In order to determine year of birth, the researchers focused on tooth enamel. Adult teeth are formed at known intervals during childhood. 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. The study found that for teeth formed after 1965, enamel radiocarbon content predicted the year of birth within 1.5 years. Radiocarbon levels in teeth formed before that year contained less radiocarbon than expected, so when applied to teeth formed during that period, the method was less precise. In order to determine year of death, researchers used radiocarbon levels in soft tissues. Unlike tooth enamel, soft tissues are constantly being made and remade during life. Thus, their radiocarbon levels mirror those in the changing environment. The study found that certain soft tissues - notably blood, nails, and hair - had radiocarbon levels identical to the contemporary atmosphere. Therefore, the radiocarbon level in those tissues postmortem would indicate the year of death. Carbon-14 dating is based on the fact that over the past 60 years, environmental levels of radiocarbon have been significantly altered by mid-20th-century episodes of above-ground nuclear weapons testing. Before this, the amount of radiocarbon in the environment varied little in the span of a century. In contrast, from 1955 to 1963, atmospheric radiocarbon levels almost doubled. Since then, they have been declining toward natural levels. Over the past six decades, the amount of radiocarbon in people or their remains depends significantly on when they were born or, more precisely, when their tissues were formed. 1 figure and 2 notes