Palaeoanthropological sites of Human Evolution of Laetoli – Olduvai Gorge

The stratigraphic sequence of both Laetoli and Olduvai gorge are associated with volcanic eruptions from the Ngorongoro Volcanic Highlands, which generated vast amounts of volcanic ash and pumice (pyroclastic material) that accumulated in the east of the Serengeti Plains. The depositional sequences are divided into a number of beds in which the footprints and hominid fossils were discovered.

The Laetoli Beds are subdivided into a Lower Unit (4.3 Ma) and Upper Unit, both composed of eolian and air-fall tuff. The lower unit is characterized by rain-printed surface and few fossils. The upper unit, dated at 3.8 Ma, is 60m thick and contains the fossils and footprints.

The Olduvai Gorge is 48Km long and 100m deep and extends to the east into the Olbalbal depression cutting through numerous layers of volcanic ash and pumice. Its stratigraphic succession is nearly 100 m thick and divided into seven formations that overlie Neoproterozoic basement rocks of the Mozambique Belt. The formations represent deposition in volcanic, alluvial fan, fluvial, aeolian, and lacustrine settings. Three million years prior to the formation of the gorge, the region was a low area periodically occupied by a large, saline lake. During this time, the lake and surrounding areas were home to earliest hominid ancestors.