Researchers trying to determine the age of deceased individuals are finding success with a new method: looking in people's mouths. Nuclear bomb testing in the 1950s, it turns out, turned everyone's teeth into radioactive clocks.

Above ground nuclear tests in the middle of the Century introduced significant amounts of radioactive carbon into the atmosphere—and into all living things. And while our skin cells are constantly regenerating, the enamel in our teeth is only made once, bearing signs of the atmosphere in which they were created. Forbes explains the science:

The element carbon usually has six protons and six neutrons, and when it does it is called carbon 12. But cosmic rays streaming into our atmosphere occasionally smash into the abundant nitrogen in our atmosphere and create a form of carbon with two extra neutrons called carbon 14....

But aboveground nuclear testing that started in 1955 released torrents of high-energy neutrons into the atmosphere. The neutrons smashed into nitrogen and created much more carbon 14 than normal.

Measuring a tooth's precise carbon make-up lets researchers zero in on when that tooth was made to a surprisingly accurate degree; in a new study, a team looked at 41 teeth and were able to determine the age of the individuals they came from within two years. Not bad.



Of course, the technique is becoming increasingly less useful as the radioactive carbon produced by the bombs bombs decays, and the method only works for individuals born during or after the 1950s. But for people whose mouths were first opened in that window, the teeth don't lie. [Forbes]