The oldest recognizable tools made by members of the family of man are simple stone choppers, such as those discovered at Olduvai Gorge in Tanzania. These tools may have been made over 1 million years ago by Australopithecus, ancestor of modern humans. Fractured stones called eoliths have been considered the earliest tools, but it is impossible to distinguish man-made from naturally produced modifications in such stones. Lower Paleolithic stone industries of the early species of humans called Homo erectus include the Choukoutienian of China and the Clactonian, Chellean-Abbevillian, Acheulian and Levalloisian represented at various sites in Europe, Africa, and Asia, from 100,000 to 500,000 years ago. Stone tools of this period are of the core type, made by chipping the stone to form a cutting edge, or of the flake type, fashioned from fragments struck off a stone. Hand axes were the typical tool of these early hunters and food-gatherers.