Radiocarbon identification of illegal ivory

Carbon-14 dating is routinely used to determine the age of organic matter going back some 60 000 years. The radioisotope, whose half-life is 5730 years, is continually produced as neutrons from cosmic rays interact with nitrogen in the atmosphere. Through photosynthesis, feeding, and respiration, ¹⁴C spreads up the food chain and equilibrates through the biosphere, but when an organism dies—or when hair, teeth, or other “permanent” tissue is formed—the isotopic fraction of ¹⁴C is locked and begins to decay. Starting in the early 1950s, the vast number of neutrons released in thermonuclear bomb tests caused the amount of ¹⁴C in the atmosphere to shoot up. At its peak a decade later, the concentration had nearly doubled; it has been falling steadily since then as atmospheric carbon gets exchanged with that in the biosphere and oceans. Through measurements on samples with known ages (including a donated tusk from Misha, seen here before she died), Kevin Uno (now at Lamont–Doherty Earth Observatory), Thure Cerling (University of Utah), and colleagues have now demonstrated that the so-called bomb curve of ¹⁴C concentration can be used with accelerator mass spectrometry to accurately determine (within 1.3 years) the age of teeth, tusks, horn, hair, and other tissue that was synthesized in the last 60 years. A 1989 international treaty and other regulations ban the ivory trade, but some exceptions are made for older ivory: In the US, for example, interstate trade is legal for ivory imported before 1989. Despite the ban, elephant poaching is now at its highest level since record keeping began in 2002, according to a 2012 report. Carbon dating thus can serve as a forensic tool to combat the illegal trade of animal parts. (K. T. Uno et al., Proc. Natl. Acad. Sci. USA 110, 10501, 2013, doi:10.1073/pnas.1222568110 . Photo courtesy of Hogle Zoo.)