University of Utah researchers developed a new weapon to fight poachers who kill elephants, hippos（河马）, rhinos and other wildlife. By measuring radioactive carbon-14 deposited in tusks（獠牙） 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. It was published online the week of July 1 in the journal Proceedings of the National Academy of Sciences.

"The dating method is affordable and accessible to government and law enforcement agencies," costing about $500 per sample, says the study's first author, geochemist Kevin Uno, who did the research for his University of Utah Ph.D. thesis.

"It has immediate applications to fighting the illegal sale and trade of ivory that has led to the highest rate of poaching seen in decades," says Uno, now a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory.

Not only can the method help wildlife forensics（辩论，取证） to combat poaching, but "we've shown that you can use the signature in animal tissues left over from nuclear weapons testing in the atmosphere to study modern ecology and help us learn about fossil animals and how they lived," says Cerling, a distinguished professor of geology and geophysics, and biology at the University of Utah.

The method uses the "bomb curve," which is a graph -- shaped roughly like an inverted "V" -- showing changes in carbon-14 levels in the atmosphere -- and thus absorbed by plants and animals in the food chain. The carbon-14 was formed in the atmosphere by U.S. and Soviet atmospheric nuclear weapons tests in Nevada and Siberia from 1952 through 1962. Those levels peaked in the 1960s and have declined ever since but still are absorbed by and measurable in plant and animal tissues.

The study was funded by the National Science Foundation, the National Geographic Society and the University of Utah. Cerling and Uno conducted it with geologist Jay Quade, a former Utah doctoral student now at the University of Arizona; Daniel C. Fisher, University of Michigan, Ann Arbor; George Wittemyer, Colorado State University; Iain Douglas-Hamilton, founder of Save the Elephants; and Samuel Andanje, Patrick Omondi and Moses Litoroh, all of the Kenya Wildlife Service.