It has long been known that radioactive isotopes in the atmosphere have made carbon dating of all kinds of materials possible. It has helped solve cold cases, revealed that Greenland sharks can live for centuries, suggested that Neanderthals died out 10,000 years earlier than previously thought, and given credence to the flood legend linked to the founding of China’s semi-mythical Xia dynasty, among many others.
Radioactive carbon released from nuclear bomb tests during the Cold War is one way of dating more recent materials. That method is now being used to help fight the illegal trade in elephant ivory. Thure Cerling, a University of Utah professor of biology, geology, and geophysics, and colleagues, published a study in late 2016 that demonstrates how radiocarbon dating, combined with genetic analysis of elephant tusks, can yield valuable clues as to when and where elephants are being poached.
The illegal ivory trade is driving elephants toward extinction. More than 30,000 are slaughtered in Africa each year, mainly to meet the demand in Asia for luxury products like carvings, jewelry, and chopsticks. The international trade has been banned since 1990, but there’s a thriving black market—and legal domestic markets within some countries remain, especially for antique ivory. It’s this loophole that has allowed some ivory traders to pass newer ivory off as antique, claiming it’s from before 1976, when elephants were first given international protections.
Cerling’s radiocarbon dating method aims to put a dent in those false claims. It works like this: From the 1940s to early ‘60s, huge amounts of radioactive carbon-14 were released into the atmosphere during open-air nuclear tests—videos of which were recently declassified. In the 1960s, in fact, the amount of carbon-14 in the atmosphere doubled. Plants took up this radioactive isotope, preserving the carbon-14 signature in its tissues.
As animals eat the plants, the isotope is transferred to them. For an elephant, the new material that grows at the base of its tusk reflects the carbon signature of the plants it recently ate. Because carbon-14 has been declining in the atmosphere since the 1960s at known levels, scientists can look at the amount of carbon-14 at the base of a tusk to determine just when that elephant died—and, therefore, whether that ivory is legal.
Cerling’s research has also provided valuable information about how ivory is reaching the black market. Most illegal ivory intercepted by law enforcement comes from elephants killed within the past two to three years, the study found, suggesting there are highly developed, organized networks for moving ivory across and out of Africa.
National Geographic spoke with Cerling about his research.
Where did the idea to carbon date elephant ivory come from?
Dating of various things, including elephant ivory, using the “bomb-curve” is fairly common in the geosciences, so this is simply another application of a commonly used method, and some other research groups have done this in the past. Our study was different in that we were able to apply this to many samples from seized ivory.
Why is this work important?
Some groups have suggested that this seized ivory was quite old, stockpiled ivory and therefore might well be legal in terms of international regulations. This method was an obvious way to test this suggestion. It showed that the ivory in the large seizures was, in fact, from quite recently killed elephants.
How exactly will knowing when an elephant died help in the fight to save elephants?
It makes a difference in how you estimate the “killing rate” of elephants in Africa if all the ivory is from recently killed elephants. It emphasizes that we need to stop the killing now, because the rate of elephant loss is not sustainable.
What are the next steps for this research?
We are now doing strontium isotope analyses to help understand where ivory comes from—the DNA provides a general region of origin, and we can further pinpoint the origins using naturally occurring stable isotopes.