The earliest directly dated Homo sapiens fossil found outside of Africa and the Levant has been uncovered in the Arabian desert, reports a study published online this week in Nature Ecology & Evolution.

Huw Groucutt, Michael Petraglia, and colleagues describe the fossil - a finger bone - which was unearthed at Al Wusta, in what is now Saudi Arabia. The authors conducted radiometric dating on the bone and determined that the finger is at least 85,000 years old. Directly dating human bones like this is more reliable than dating based on overlying sediments or associated materials alone, but is not always possible. For the Al Wusta finger bone, the authors were also able to corroborate the dates from surrounding animal remains and sediments using electron spin resonance and optically stimulated luminescence techniques.

At the time the finger was buried, the climate of the region around Al Wusta was humid and monsoonal. The authors conclude from this early incursion into a 'Green Arabia' that human dispersal out of Africa might have been aided by this enhanced summer rainfall, leading migrating humans to occupy not only the woodlands of the Levant that were sustained by winter rainfall, but also such semi-arid grasslands in the Arabian interior as Al Wusta. The authors suggest that adapting to this new environment would have been an early step on Homo sapiens' path to global success.