Chronology of the Acheulean to Middle Stone Age transition in eastern Africa
The origin of the Middle Stone Age (MSA) denotes the transition from a highly persistent mode of stone toolmaking, the Acheulean, to a period of increasing technological innovation and cultural indicators associated with the evolution of Homo sapiens. Here we use 40Ar/39Ar and U-series dating to calibrate the chronology of Acheulean- and early MSA-rich sedimentary deposits in the Olorgesailie Basin, South Kenya Rift. We establish the age of late Acheulean tool assemblages from 615 to 499 ka, after which a large technological and faunal transition occurred, with definitive MSA lacking Acheulean elements beginning most likely by ~320 ka, but at least by 305 ka. These results establish the currently oldest repository of MSA in eastern Africa.