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25-545: Olorgesailie is a geological formation in East Africa , on the floor of the Eastern Rift Valley in southern Kenya , 67 kilometres (42 mi) southwest of Nairobi along the road to Lake Magadi . It contains a group of Lower Paleolithic archaeological sites. Olorgesailie is noted for the large number of Acheulean hand axes discovered there that are associated with animal butchering. According to

50-446: A facies , stratum , bed , seam , lode etc. Thickness is measured at right angles to the surface of the seam or bed and thus independently of its spatial orientation. The concept of thickness came originally from mining language, where it was used mainly to indicate the workability of seams. It has since become an established term in earth science , for example in geology, for the depth of sedimentary rocks , in hydrogeology for

75-611: A geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at

100-409: A hilly area full of sedimentary outcrops, had removed the geologic layers representing some 180,000 years of time at exactly the period of this evolutionary transition. Due to this, his team had to drill for sediments. They arranged to have a Nairobi company drill in the nearby Koora basin, extracting sediment from as deep into the earth as they could. The drill site, about 24 kilometres (15 mi) from

125-542: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

150-617: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

175-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

200-459: Is 900,000 to 970,000 years old and probably belonged to Homo erectus , thereby making it the first human fossil found on the site. The fossil remains were in the same stratigraphic level as two hand axes and several flakes, near dense deposits of hand axes. In 2018, evidence dating to about 320,000 years ago was found at Olorgesailie of the early emergence of complex and modern behaviors, possibly associated with early Homo sapiens , including:

225-430: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Thickness (geology) Thickness in geology and mining refers to the distance across a packet of rock , whether it be

250-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

275-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

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300-563: The National Museums of Kenya , the finds are internationally significant for archaeology, palaeontology , and geology. The artifacts were first discovered by the British geologist John Walter Gregory in 1919, but it was not until 1943 that excavation began in earnest under the direction of Mary and Louis Leakey , with the assistance of paroled Italian prisoners of war . Work continued there until 1947. Glynn Isaac took up

325-603: The 21 October 2020 issue of the journal Science Advances , an interdisciplinary team of scientists led by Richard Potts, director of the Human Origins Program at the Smithsonian's National Museum of Natural History, described the prolonged period of instability across the landscape in this part of Africa (now Kenya) that occurred at the same time humans in the region were undergoing a major behavioral and cultural shift in their evolution. Erosion at Olorgesailie,

350-540: The National Museum of Natural History's Human Origins Program and Department of Paleobiology and dozens of collaborators at institutions worldwide worked to analyze the environmental record they had obtained, which is now the most precisely dated African environmental record of the past 1 million years. They found that after a long period of stability, the environment in this part of Africa became more variable around 400,000 years ago, when tectonic activity fragmented

375-603: The Olorgesailie basin. Subsequent sedimentation covering the site has preserved the fossils and created a stratigraphy which helps in dating them. Existing temporary lakes and swamps give evidence of a humid climate during the middle Pleistocene. Sediments left by the lake cover an area of about 130 km (50 sq mi). Of the artefacts, 99% were made from locally derived lavas , particularly trachyte , although small amounts of quartzite and obsidian have been found, indicating transportation over 16 to 40 km. In

400-475: The archaeological dig sites, was a flat, grassy plain, and the team had no clear idea what was beneath its surface. With the involvement and support from the National Museums of Kenya and the local Oldonyo Nyokie community, a 139-meter core was removed from the earth. That cylinder of earth, just four centimeters in diameter, turned out to represent 1 million years of environmental history. Colleagues in

425-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

450-535: The excavation in the 1960s for his dissertation. In the 1980s, research was continued by Richard Potts of the Smithsonian Institution in conjunction with the National Museums of Kenya . Human tools are the most prominent of all historic items in the area. The abundant hand axes are characteristic of the Acheulean period, made by hominins between about 600,000 and 900,000 years agoalong what

475-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

500-420: The landscape. By integrating information from the drill core with knowledge gleaned from fossils and archeological artifacts, they determined that the entire ecosystem evolved in response. 1°34′40″S 36°26′46″E  /  1.577878°S 36.446228°E  / -1.577878; 36.446228 Geological formation A formation must be large enough that it can be mapped at the surface or traced in

525-524: The same period, and it is suggested that complex behaviors began in Africa around the time of the emergence of Homo sapiens . Preservation of the Aechulean hand axe culture was made possible by heavy falls of alkaline ash from volcanoes near the site that were active at the time. Mount Suswa and Mount Longonot are volcanoes, and their vents are likely to have contributed to the ash that accumulated in

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550-407: The subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of

575-643: The surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

600-413: The trade and long-distance transportation of resources (such as obsidian), the use of pigments, and the possible making of projectile points. The emergence of these behaviors, it is observed by the authors of three 2018 studies on the site, approximately corresponds to the earliest known Homo sapiens fossil remains from Africa (such as at Jebel Irhoud , Morocco and Florisbad , South Africa) dated to about

625-418: Was then the shore of a now dried-up lake. Fossils of various animals have also been found, including those of extinct species of hippo, elephant, zebra, giraffe, and baboon, likely to have been butchered with the aid of the hand axes. In June 2003, a team led by Potts discovered a frontal bone in situ . Other parts of the small skull (designated KNM-OL 45500) were found in following months. The frontal bone

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