Why is Olduvai Gorge such an important locality for studies of early hominids? There are a number of reasons.
First, the area around the gorge witnessed the progressive ebb and flow of lake sediments and periodic falls of volcanic ash over the past several million years. These periodic phenomena not only provided excellent conditions for the preservation of non-hominid animal and hominid fossils, but also for archaeological clues to their habitat and behavior. The volcanic activity in the area, from the Ngorongoro and other nearby volcanoes, provided tuffs and lava flows that can be dated using the potassium-argon method. The wealth of non-hominid fossils found in the strata provide excellent materials for biostratigraphic cross-dating between areas without good datable rocks, as well as providing clues to changes in habitat and climatic conditions.
Second, Pleistocene and Recent faulting and erosion created the gorge itself, a slice through over 200 feet of archaeologically and paleontologically rich deposits. Without this exposure of the fossil beds, they never would have been discovered. Without the long sections of exposed stratigraphy, it would have been difficult to fully assess the chronological relationships between the various fossil localities found up and down both branches of the Gorge.
As a result, Olduvai Gorge preserves and, makes available for observation, dateable deposits that cover both species of Australopithecine as well as species of the genus Homo through modern Homo sapiens sapiens. It also documents developments in stone tool technology over a 2 million year period, as well as changes in the habitats occupied by these hominids and their animal neighbors.