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,