Olduvai Gorge basalt. Basalt stones at the Olduvai River in Olduvai Gorge, Tanzania. This gorge (also called Oldupai Gorge) is famous for fossils discovered here of extinct hominins that form part of the human evolutionary tree. It is sometimes called The Cradle of Mankind. The gorge was formed as a river eroded its way through volcanic ash deposited millions of years ago on the shores of a large lake. Basalt and flint would have been used to make stone tools. Fossils discovered here include Paranthropus boisei, Homo habilis, and Homo erectus. The work was pioneered by Louis Leakey and Mary Nicol (later Leakey) in the 1930s and 1950s.