Few megafauna are more charismatic than elephants, and that charisma gives them political clout. On July 1st, for example, Barack Obama used the Tanzanian leg of his tour of Africa to announce an executive order intended to give teeth to America’s obligation, as a party to the Convention on International Trade in Endangered Species, to prevent the smuggling of poached ivory.
The rules on trading ivory, though, are hard to enforce, for if it comes from an animal killed before 1990 such trade is legal. Not surprisingly, a cottage industry in making ivory look older than it is has grown up. But a paper published in the Proceedings of the National Academy of Sciences, by Kevin Uno of the University of Utah and his colleagues, may deal with that. For Dr Uno has worked out how to use one of science’s less glorious episodes, the atmospheric testing of nuclear weapons, to work out exactly how old a piece of ivory really is.
Dr Uno’s method uses the ivory’s carbon-14 content in a way that was not previously employed. What radiochemists call 14C forms naturally in the atmosphere by the action of cosmic rays on nitrogen atoms. It has a half-life of 5,730 years, which makes it ideal for dating objects pertinent to human history, and it can do so to within a few decades of their true age—which is great for archaeology. It is not, though, much use for finding out whether a particular piece of ivory was detached from the elephant that grew it before or after a specific date just over 20 years ago. But Dr Uno realised there has recently been a second source of 14C—those bomb tests. And they give him the precision he requires.
Normally, the amount of 14C in the atmosphere is governed by the rate at which cosmic radiation creates it and the rate at which things like photosynthesis absorb it. More....