Oldupai Gorge and Laetoli

Abstract

The palaeoanthropological sites of Oldupai Gorge (previously known as Olduvai) and Laetoli are located on the Eastern Serengeti Plains, at the foot of the Ngorongoro Highlands, northern Tanzania. Hominin fossils and Oldowan stone tools have been unearthed from Plio-Pleistocene sequences of lacustrine sediments and volcanic ashes exposed in a shallow ravine carved by the ephemeral Oldupai River. The sediments and ashes accumulated in a small basin which formed due to warping of the regional plateau. Warping was triggered by the southward propagation of the East African Rift System (EARS). The presence of repetitive layers of water-lain volcanic ashes, or tuffs, derived from the Ngorongoro Volcanism, is particularly significant as they yield precise radiometric dates. Bed I of the Oldupai Group, where the first discoveries of Zinjanthropus boisei (OH-5) and Homo habilis (OH-7) were made by Mary Leakey, in 1959 and 1960, has an age of 2.015–1.803 Ma. The age of these two, partially intact hominin skulls has been determinded as 1.848 Ma (OH-5) and 1.848–1.832 (OH-7). Oldupai Gorge has also yielded fossils of Homo erectus (1.2–0.70 Ma) and the coexistence of different species of hominin is a unique feature of the locality. Reactivation of faulting associated with the Gregory Rift at approximately 1.15 Ma caused some of the older deposits to be reworked and buried beneath younger sediments and ashes. The youngest component of the Oldupai Group comprises wind-blown volcanic ashes from volcanoes located in the Gregory Rift Valley near Lake Natron. The Laetoli site has yielded hominin fossils and footprints from an area, where the Pliocene-age Laetoli Group is exposed in shallow gullies and areas of badland erosion. The most significant find is the 27-m-long trail made by Australopithecus afarensis (dated at 3.6 Ma), discovered by Paul Adell in 1978. The footprints are preserved in volcanic ash derived from the Sadiman Volcano.