What is Olduvai Gorge?
[[File:Olduvai Gorge or Oldupai Gorge.jpg|thumb|300px|Olduvai Gorge]] [[File:Oldupai Gorge monolith.jpg|thumb|Close-up of monolith]] [[File:Olduvai ast.jpg|thumb|Olduvai Gorge from space]] [[File:Olduvai gorge topo.jpg|thumb|Topography of Olduvai Gorge]] The '''Olduvai Gorge''' is a steep-sided [[ravine]] in the [[Great Rift Valley]] that stretches through [[East Africa]]. It is in the eastern [[Serengeti|Serengeti Plains]] in northern [[Tanzania]]. The [[gorge]] is about {{convert|48|km|mi|abbr=on}} long. It is {{convert|45|km|abbr=off}} from the [[Laetoli]] archaeological site. The gorge is a highly important [[prehistoric]] site for the study of [[human evolution]]. It was once a [[lake]], and got covered by layers of [[volcanic ash]].<ref name=Hay>Hay, Richard L. 1976 ''Geology of the Olduvai Gorge''. University of California Press.</ref> This site was occupied by ''[[Homo habilis]]'' about 1.9 million years ago, ''[[Paranthropus boisei]]'' 1.8 million years ago, and ''[[Homo erectus]]'' 1.2 million years ago. ''[[Homo sapiens]]'' occupied the site 17,000 years ago. The name is a misspelling of '''Oldupai Gorge''', which was adopted as the official name in 2005. Oldupai is the [[Maasai language|Maasai]] word for the wild sisal plant ''[[Sansevieria ehrenbergii]]'', which grows in the gorge. == Geology == Millions of years ago, the site was that of a large [[lake]], the shores of which were covered with successive deposits of [[tuff|volcanic ash]]. About 500,000 years ago [[Earthquake|seismic activity]] diverted a nearby stream which began to [[Erosion|cut down]] into the [[sediment]]s, revealing seven main [[Stratum|layers]] in the walls of the gorge. The geology of Olduvai Gorge and the surrounding region was studied in detail by Richard L. Hay,<ref name=Hay/> who worked at the site between 1961 and 2002. The [[stratigraphy]] is extremely deep and layers of volcanic ash and stones allow [[radiometric dating]] of the embedded artifacts, mostly through [[K–Ar dating|potassium–argon dating]] and [[argon–