Olduvai Gorge, Tanzania. This gorge (also called Oldupai Gorge) is famous for the 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. The erosion revealed the strata (rock layers) in the walls of the gorge. Fossils discovered here include those of Paranthropus boisei, Homo habilis, and Homo erectus. These discoveries were pioneered by Louis Leakey and Mary Nicol (later Leakey) in the 1930s and 1950s.