By Zaineb Mohammed
Ivory poachers may have finally met their match: forensic science. A study just published by PNAS describes a carbon-dating technique making it possible to determine the age of elephant tusks—and thus whether a particular piece of ivory has been acquired illegally.
The method involves measuring the radiocarbon—a radioactive isotope of carbon—at the base of a tusk to learn when the elephant died. Kevin Uno, the lead author on the study and a postdoctoral researcher at the Lamont-Doherty Earth Observatory, broke down how it all works: "Plants absorb carbon dioxide and it gets locked into the leaf. Then some elephant walks by, eats that plant, and then builds its tissue, either tusk or hair, from the plant it ate."
As Uno explained, new tissue forms every day in the elephant's tusk as it eats, with the base containing the newest tissue. Because the carbon absorbed by plants contains radiocarbon from the atmosphere, researchers can match the radiocarbon level in the tissue. But the key to the technique is something that scientists call the "bomb curve," the period between 1952 to 1962 during which radiocarbon nearly doubled because of nuclear weapons testing. After the test ban treaty went into effect in 1963, the concentration of radiocarbon in the atmosphere has been diluted at a steady rate. Researchers used samples from primate hair, hippopotamus canines, elephant tusks, and an oryx horn to test their technique.
As the study explains, "Bomb-curve dating of confiscated animal tissues (e.g., ivory statues) can be used to determine whether trade of the item is legal, because many Convention of International Trade of Endangered Species restrictions are based on the age of the tissue." Because elephants are threatened by extinction, CITES declared a ban on the trade of tusks from African elephants in 1989 and those from Asian elephants in 1975. More....