Olduvai biface stone tool (hand axe). Silhouette of a prehistoric hand axe stone tool against the setting Sun. This stone tool was discovered at Olduvai Gorge, Tanzania. This gorge (also called Oldupai Gorge) is famous for the fossils discovered there of extinct hominins that form part of the human evolutionary tree. Rocks such as basalt and flint were used to make these tools. The earliest finds date from around 2 million years ago. Fossils found here include those of Paranthropus boisei, Homo habilis, Homo erectus, and Homo sapiens.