Laser-fusion 40Ar/39Ar dating of Bed I, Olduvai Gorge, Tanzania

BED I of Olduvai Gorge has yielded some of the most important hominid fossils in the world, but precise age estimates have been elusive. Here we report new dating results for Bed I, based on 40Ar/39Ar analyses of single mineral grains using the laser-fusion technique. These dates reveal that the fossiliferous deposits of middle to upper Bed I, a period of significant biological and climatic change, comprise an extremely brief interval of time, from 1.80 Myr to 1.75 Myr. Dates for lower Bed I suggest that the base of the Olduvai subchron, of the geomagnetic polarity timescale, may be around 100,000 yr older than the currently accepted value.