Dropping the Bomb on Poaching

Radiocarbon dating of elephant tusks can help identify illegal ivory. 

It’s been tough going for pachyderms in recent years. Elephant poaching has spiked, and seizures of ivory have reached their highest point since an international trade ban came into effect in 1989, according to a 2012 report by the Convention on International Trade in Endangered Species (CITES). At an estimated rate of 30,000 animals slaughtered every year, elephants could become extinct in fifteen to twenty years. A new application of a forensic technique for dating elephant tusk ivory, however, could help stem the tide. The method would assist authorities in differentiating legal, pre-1990 ivory from that hacked off of illegally slaughtered animals.

The tusk-dating concept relies on a rather unexpected source: the aboveground testing of nuclear weapons. From 1952 to 1962, those explosions almost doubled the amount of radioactive carbon 14 (radiocarbon) in the atmosphere. As plants have absorbed the radiocarbon, its levels have steadily fallen over time, forming a so-called bomb curve. Researchers can use this curve to judge when plants— and animals that ate the plants—produced certain tissues.

Kevin T. Uno, now a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory, and colleagues tested twenty-nine tissue samples of known ages, including elephant tusks, teeth, and tail hairs as well as hippopotamus teeth, monkey hair, and plant matter. The team used an accelerator mass spectrometer to radiocarbon date the samples and compared their results against the bomb curve. As it turned out, those specimens formed after 1955 could be accurately dated, in some cases to within a year of their formation by the animal in question.

Applying this method in the field could thus help in the task of identifying illegal ivory, which until now has proved problematic. “In many cases, we can determine when the elephant was killed or when the tusk stopped growing,” said Uno. “This method fills a major gap in the forensic toolkit to combat poaching and illegal trade.” (Proceedings of the National Academy of Sciences)