African Elephant Ivory Tracked With Carbon-14 Dating
July 2, 2013

Illegal Ivory Can Be Traced With Carbon-14 Dating

April Flowers for - Your Universe Online

Almost 25 years ago, an international ban was placed on the sale of ivory to slow the tide of elephant deaths. Currently, the slaughter rate for African elephants is such that they might be extinct before the end of the century if it continues unchecked. The ban allows ivory harvested before 1989 to continue being sold, which puts the burden on law enforcement to distinguish between legal and poached ivory.

A team of researchers, led by Columbia University's Lamont-Doherty Earth Observatory, has developed a new method for dating elephant tusks, which could make it easier to enforce the ivory ban and save the African elephant from extermination. The team says this method, described in the Proceedings of the National Academy of Sciences, could also be applied to endangered rhinoceroses and other wildlife.

"We've developed a tool that allows us to determine the age of a tusk or piece of ivory, and this tells us whether it was acquired legally," said the study's lead author, Kevin Uno, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory. "Our dating method is affordable for government and law enforcement agencies and can help tackle the poaching and illegal trade crises." Uno, a geochemist at Columbia, performed the research for this study for his University of Utah PhD 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.

"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, a distinguished professor of geology and geophysics, and biology at the University of Utah.


The tusk of an elephant grows ring by ring, making a record of what plants the animal ate. It turns out, the tusk also records how much radioactive carbon was in the air. This gives the researchers a time marker for the elephant's meals. Plants absorb radiocarbon put into the air by nuclear weapons testing in the 1950s and 1960s - performed by the US in Nevada and the USSR in Siberia - during photosynthesis. This plant-stored radiocarbon travels up the food chain, finally ending up in the fingernails, hair, teeth and tusks of animals. Scientists compare the radiocarbon present in those tissues against the fluctuating "bomb curve" of radiocarbon in the atmosphere, pinpointing when the tissues formed. Sometimes, they are even able to tell when the animal died. This method is effective for tissues formed from around 1955 until the bomb curve, or concentration of carbon 14 isotopes in the air, subsides to background levels around 10 to 15 years from now. The half-life of carbon-14 is around 5,700 years.

Because the market for legal ivory is so highly regulated, finding tusks for scientific research is difficult. The group was able to gain access to the tusks of two elephants with the help of a Salt Lake City Zoo and several agencies in Kenya. The two elephants were Misha, who was euthanized at Utah's Hogle Zoo in 2008, and Amina, who died naturally at Kenya's Samburu National Preserve in 2006. The Hogle Zoo was willing to work with the team because when they were contacted they had not yet buried Misha. When the team traveled to Kenya for Amina's tusk, they were watched closely by the Kenya Wildlife Service as they sawed the tusk into domino-sized samples.

The research team measured radiocarbon levels at the base of each tusk in order to independently verify the elephants' death. To validate the method with tissue samples of different ages, similar tests were done on monkey hair, hippo canines, oryx horn, elephant tail hairs, and some grasses collected in Kenya in 1962. Obtaining precise ages came down to two key steps. First, each tusk was sampled lengthwise along the growth ring. The team then used the most advanced technology available - an accelerator mass spectrometer (AMS) - to measure the radiocarbon. AMS requires 1,000 times less material for analysis than conventional carbon-14 dating, giving researchers a big advantage when sampling fossils or small pieces of worked ivory. Materials analyzed with AMS are bombarded with cesium atoms, which sputter off carbon atoms so the ratio of carbon-14 to carbon-12 can be measured.

They also measured the growth rates for the teeth. This measurement can be applied to elephant teeth in the fossil record to understand how climate and vegetation varied in Africa when humans were evolving. The team says this method has other wildlife forensic applications, including dating rhino horns, which are intensely sought after for their perceived medicinal benefits.

This new method complements a forensic tool developed by the University of Washington's Center for Conservation Biology. The UW tool allows researchers to track ivory seizures back to their source. Sam Wasser, center director, laid out a map of African elephant populations based on DNA from their dung in a 2004 study. The map, when matched against a piece of seized ivory, could tell investigators where the ivory originated. Law enforcement has used this DNA tool to identify where elephants are being poached; the new radiocarbon tool tells them when. "It can reliably tell us, is it legal ivory or not?" said Wasser, who was not involved in the current study.


A 2012 report by the Convention on International Trade in Endangered Species (CITES) reveals that since record keeping began in 2002, elephant poaching is at an all-time high. Experts say more elephants are slaughtered today, at the rate of nearly 30,000 a year, than before the 1989 ban. The International Union for Conservation of Nature's elephant database reports only some 423,000 African elephants remain.

The majority of the illegal ivory leaves the African continent through Tanzania and Kenya. It ends up in Asia, where it is carved into religious icons, decorative art and signature seals popular among the Chinese and Japanese. China imports nearly 70 percent of the illegal ivory, with the US being the next biggest market. In the US, ivory is worked into the handles of guns and knives, said Richard Ruggiero, an expert at the US Fish and Wildlife Service. In 2011, global seizures of smuggled ivory reached a new record at 86,000 pounds. This equals nearly 6,000 elephants. Law enforcement is no match for the sheer size of the problem, however. "With poaching rising exponentially because of exploding demand we are actually losing ground," said Ruggiero.

In 2004, a kilogram (approximately 2.2 pounds) of ivory was priced at $200; in 2007, that had risen to $850. These rising prices are driving Africa's notorious militias, including the Lord's Resistance Army in northern Uganda and south Sudan, the Shabab in Somalia and the Janjaweed of Darfur to kill elephants for tusks to buy guns.

Ecologists warn the disappearance of the African elephant will be farther reaching than just the loss of a majestic, highly intelligent creature. It might mean a structural change to the ecosystems of the African savannahs and rain forests. "They are environmental architects," said Wasser. "They keep woods down in the savannah and are the most important dispersers of seeds of rain forest trees. The central African rain forest is the second most important area on earth for capturing carbon dioxide and storing it."

Cerling says while the method's use against poaching is important, the scientific importance is the new understanding of time in the formation of animal tissues and how diet and physiology is recorded in those tissues over time. The new method will improve our understanding of the diets of modern and prehistoric animals, especially when combined with existing isotope analysis of ratios of carbon-13 to carbon-12 in teeth. This data will reveal whether animals ate diets based on tree and shrub leaves and fruits, or upon grasses and grazing animals.

To continue their study, the team analyzed another 41 samples, determining the growth rates from tusks and tusks and teeth from elephants and hippos, and elephant tail hair. Using this information, researchers can extrapolate the growth rates of tusks, teeth and hair to fossil or modern elephants and other animals, which "will help us improve the chronology of the diet history of an individual fossil or modern animal," Cerling says.