Although there were early hominids in southern Africa, the majority of their fossils come from East Africa, notably from the Hadar region of Ethiopia and from Kenya and Tanzania, particularly around Lake Turkana and Lake Victoria, along the line of the great African Rift Valley.
Whereas most remains of the distant past are deeply buried, continual tectonic activity along the Rift Valley, coupled with river downcutting (the progressive deepening of river valleys), has exposed large sectors of previously buried sediments in which fossils, including those of hominids (human ancestors - members of the genera Australopithecus and Homo), may be found.
These sediments are often sandwiched between layers of datable volcanic tuff (a porous stone), providing approximate dates for the fossils.
Many important pieces of the jigsaw of human origins have been recovered from this zone: Australopithecines from Hadar, Homo habilis and H. erectus from Lake Turkana, and the first known early hominids from the famous site of Olduvai.
One to two million years ago Olduvai Gorge was a lake basin occupied by many animals including several hominid species. Finds of animal bones and stone tools indicate that Homo were butchering scavenged animal carcasses.
