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In contrast, from 1955 to 1963, atmospheric radiocarbon levels almost doubled.
Since then they have been dropping back toward natural levels.
To determine year of birth, the researchers focused on tooth enamel.
Adult teeth are formed at known intervals during childhood.
Unlike tooth enamel, soft tissues are constantly being made and remade during life.
Thus, their radiocarbon levels mirror those in the changing environment.
They found that for teeth formed after 1965, enamel radiocarbon content predicted year of birth within 1.5 years.However, more testing is needed to confirm that belief. 269, March 2012NCJ 237722 Philip Bulman is a writer and editor at NIJ.Danielle Mc Leod-Henning is a program manager and physical scientist at NIJ. 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.
The researchers found that certain soft tissues — notably blood, nails and hair — had radiocarbon levels identical to the contemporary atmosphere.