Customs and authorities are often powerless against the flood of illegal ivory. The biggest problem is that in the US and some other countries, African ivory objects made before 1989 are still allowed to be imported and traded. An exact age determination of such pieces was hardly possible - until now. "We have developed a method that allows us to determine the age of a piece of ivory or a tusk at an affordable price, " says lead author Kevin Uno of the University of Utah. In tests with 29 samples of animal hair, tusks and other animal and plant materials of different ages, the researchers managed to date them precisely down to the year.
C-14 from nuclear weapon explosions as a dating aid
The new method is based on the so-called bomb curve - the atmospheric changes caused by the nuclear tests of the 1950s and 60s. The explosions of the nuclear weapons caused much of the heavy carbon isotope C-14 in the atmosphere. As a result, the C-14 levels increased sharply from 1952 and dropped slowly after the end of the nuclear weapons tests in the early 1970s again. The C-14 also enters the plant and animal tissues via carbon dioxide and the food chain. If one compares the content of this carbon isotope with the known curve of the atmospheric C-14 values, one can conclude from this, when an animal last built carbon into its body - and thus, when it probably died. display
In the case of the elephants, this balance is particularly well possible because the tusks grow a little bit further year after year, with the youngest section lying directly at their base. If you measure the C-14 content there, you can determine when the elephant died. For their study, the researchers used the so-called accelerometer mass spectrometry (AMS). In this method, the sample is bombarded with cesium atoms. Upon impact, these precipitate carbon atoms from the material, the iosotopic ratio of which can then be determined. The big advantage: The analysis requires a thousand times less material than previous C-14 tests and it goes fast, as the researchers report. "It could therefore be used well to date seized ivory and determine whether it is legal or illegal, " said co-author Thure Cerling of the University of Utah.
The process could also help combat on-site poaching more effectively: In 2004, a University of Washington researcher created a distribution map of African elephant populations using waste DNA samples. Based on traces of genetic material in ivory its origin can be traced so. Combining this with the C-14 dating, one can not only tell more accurately when the elephant was killed, but also where - and take appropriate protective measures for the rest of the population. How necessary that is, the latest figures from the International Union for Conservation of Nature (IUCN) show that only around 423, 000 African elephants now roam the savannahs and forests of Africa - and there are fewer and fewer.Kevin Uno (University of Utah, Salt Lake City) et al., Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073 / pnas.1302226110 © science.de - === Nadja Podbregar