In the study, the researchers used accelerator mass spectrometry, or AMS, which requires 1,000 times less material for analysis – a big advantage when sampling fossils or small pieces of worked ivory, Cerling says.
Understanding Ancient and Modern Ecosystems While the method's use against poaching is important, "the scientific part is the importance of understanding time in the formation of animal tissues and how diet and physiology is recorded in those tissues over time" as they grow, Cerling says.
Cerling says that will improve understanding of what prehistoric and modern animals ate over time, especially when combined with existing isotope analysis of ratios of carbon-13 to carbon-12 in teeth – data that reveal whether animals ate diets based on tree and shrub leaves and fruits, or upon grasses and grazing animals.
This African elephant has what are believed to be the biggest tusks among elephants at Kenya's Samburu National Reserve.
Illegal poaching of some 30,000 elephants a year for their ivory tusks threatens the animals with extinction.
By measuring radioactive carbon-14 deposited in tusks and teeth by open-air nuclear bomb tests, the method reveals the year an animal died, and thus whether the ivory was taken illegally.
"This could be used in specific cases of ivory seizures to determine when the ivory was obtained and thus whether it is legal," says geochemist Thure Cerling, senior author of a study about the new method.
The method in the study is a bit like telling a tree's age by its rings, but instead of counting rings, Cerling, Uno and colleagues measured carbon-14 levels at various points along the lengths of elephants' and hippos' tusks and teeth.
The conventional way of measuring carbon-14 is to wait for and count when the isotope decays radioactively.
Ivory Trade Drives Elephant Slaughter International agreements banned most trade of raw ivory from Asian elephants after 1975 and African elephants after 1989.
In the United States, raw and worked African ivory (jewelry, figurines, gun and knife handles) is legal if it was imported before 1989 or, if worked ivory is imported after, it must be at least 100 years old.
The researchers tested the accuracy of carbon-14 dating in 29 animal and plant tissues killed and collected on known dates from 1905 to 2008.