The Olduvai Gorge or Oldupai Gorge is a paleoanthropological site in northern Tanzania. Many sites exposed by the gorge have proven invaluable in furthering understanding of early human evolution. A steep-sided ravine in the Great Rift Valley that stretches across East Africa, it is about 48 km (30 mi) long, and is located in the eastern Serengeti Plains within the Ngorongoro Conservation Area in the Olbalbal ward located in Ngorongoro District of Arusha Region, about 45 kilometres (28 miles) from Laetoli, another important archaeological locality of early human occupation. The British/Kenyan paleoanthropologist-archeologist team of Mary and Louis Leakey established excavation and research programs at Olduvai Gorge that achieved great advances in human knowledge. The site is registered as one of the National Historic Sites of Tanzania. The gorge takes its name from the Maasai word oldupai which means "the place of the wild sisal" as the East African wild sisal (Dracaena hanningtonii) grows abundantly throughout the gorge area. Twenty-five kilometers downstream of Lake Ndutu and Lake Masek, the gorge is the result of up to 90 m (300 ft) erosion cutting into the sediments of a Pleistocene lake bed. A side gorge, originating from Lemagrut Mountain, joins the main gorge 8 km (5.0 mi) from the mouth. This side gorge follows the shoreline of a prehistoric lake, rich in fossils and early hominin sites. Periodic flows of volcanic ash from Olmoti and Kerimasi helped to ensure preservation of the fossils in the gorge. The locality is significant in showing the increasing developmental and social complexities in the earliest Hominina, largely revealed in the production and use of stone tools. Prior to tools, evidence of scavenging and hunting can be noted—highlighted by the presence of gnaw marks that predate cut marks—and of the ratio of meat versus plant material in the early hominin diet. The collecting of tools and animal remains in a centralised area is evidence of developing social interaction and communal activity. All these factors indicate an increase in cognitive capacities at the beginning of the period of hominids transitioning to homininina—that is, to human clade. Homo habilis, probably the first early human species, occupied Olduvai Gorge approximately 1.9 million years ago (mya); then came a contemporary australopithecine, Paranthropus boisei, 1.8 mya, followed by Homo erectus, 1.2 mya. Homo sapiens, which is estimated to have emerged roughly 300,000 years ago, is thought to have occupied sites in the gorge 17,000 years ago.
History
Discovery and research
While travelling in German East Africa in 1911 to investigate sleeping sickness, German physician and paleontologist Wilhelm Kattwinkel visited Olduvai Gorge, mistakenly naming it Oldowan , where he observed many fossil bones of an extinct three-toed horse. Inspired by Kattwinkel's discovery, German geologist Hans Reck led a team to Olduvai in 1913. There, he found hominin remains which were later radiocarbon dated to 17,000 BP. Four more expeditions were planned, but World War I prevented their start. After the war, as Tanganyika came under British control, Louis Leakey visited Reck in Berlin and viewed the Olduvai fossils. Louis Leakey became convinced that Olduvai Gorge held stone tools, thinking the deposits were of similar age to the Kariandusi prehistoric site in Kenya. Reck and the paleontologist Donald McInnes accompanied Louis Leakey in his 1931 expedition, where Louis found a number of hand axes close to camp soon after their arrival. Mary Leakey first visited the area in 1935, joining Louis and Percy Edward Kent. Subsequent visits were made by the Leakeys in 1941, 1953, 1955 and 1957. Louis and Mary Leakey are responsible for most of the excavations and discoveries of the hominin fossils in Olduvai Gorge. In July 1959, at the FLK site (the initials of the person who discovered it Frida Leakey, and K for korongo, the Swahili language word for gully), Mary Leakey found the skull of Zinjanthropus or Australopithecus boisei. In addition to an abundance of faunal remains the Leakeys found stone tools Mary classified as Oldowan. In May 1960, at the FLK North-North site, the Leakeys' son Jonathan found the mandible that proved to be the type specimen for Homo habilis.
Archaeology and geology
Hans Reck and Richard Hay While Hans Reck was the first geologist to attempt to understand the geology of the gorge, current understanding of the geology of the stratigraphic sequence of Olduvai Gorge was made possible in large part by the efforts of geologist Richard Hay. Hay spent twelve years studying the geology at Olduvai, much of it working along with Mary Leakey, finally formulating a detailed picture of the geologic history of the area. Hay's seminal work The Geology of the Olduvai Gorge was published in 1976. Reck identified five main layers of deposition in the gorge, which were labelled Beds I through V, with Bed I being the oldest and lowest in the sequence. Hay and other geologists working at the gorge since Reck's time have utilized Reck's original Bed outline, adding clarity, detail, and corrections to achieve a more thorough understanding of gorge history. Reck's original Bed IV interval was later distinguished as consisting of Bed IV and the Masek Beds, while Bed V has been reclassified as the Ndutu Bed and the Naisiuiu Bed.
Gorge stratigraphy The stratigraphic sequence in the gorge is up to 90 m (300 ft) thick, with a welded tuff, the Naabi ignimbrite, forming the base. This is overlain by a series of lava flows from Olmoti and from another source to the south. The oldest fossils are found on this surface, dated at 1.89 mya, while stone tools have been dated at 1.7 mya through the first use of K-Ar dating by Garniss Curtis. In addition, fission track dating and paleomagnetism were used to date the deposits, while amino acid dating and Carbon-14 dating were used to date the bones. Hominid fossils and stone tools are found continuously throughout the entire exposed sequence in the gorge. Faulting between 100 and 30 kya, formed the Olbalbal Depression northwest of Ngorongoro.
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