By Ker Than
A new study, published in the Proceedings of the National Academy of Sciences, shows that carbon-14, a radioactive version of the common carbon atom, can be used to determine when an animal died to within about one year."We're not the first to try this, but I think we've done the most thorough proof of concept," said the study’s first author Kevin Uno, a geochemist at Columbia University's Lamont-Doherty Observatory.
The dating technique could help wildlife investigators for the first time to reliably determine if ivory was obtained legally by indicating whether it was acquired after a 1989 international ban on trade in ivory.
"You can sometimes guess that ivory is old by examining it, but I think this is a much more accurate and precise method for doing that," said biologist Alfred Roca of the University of Illinois, who was not involved in the research.
Nuclear bomb testing
Carbon-14 is produced naturally by cosmic rays interacting with atoms in the Earth's atmosphere. But in the 1950s and 1960s, the United States and the former Soviet Union conducted hundreds of aboveground nuclear bomb tests that nearly doubled the concentration of carbon-14 in the atmosphere.
The aboveground explosions were banned in 1963, and since then the concentration of carbon-14 has been steadily declining as natural processes remove it from the atmosphere. One way that this happens is that plants and animals in the food chain absorb the carbon atoms, explained study coauthor Thure Cerling, a geochemist at the University of Utah.
"It gets into plants during photosynthesis and is made into plant sugars and starches," Cerling said. "And then an animal comes along and eats the plant and makes it into hair or muscle or eyeballs, and it gets incorporated into those tissues." More....