The provenance and age of two Homo sapiens fossils (Omo I and Omo II) from the Kibish Formation in southern Ethiopia have been much debated. Here we confirm that Omo I and the somewhat more primitive-looking Omo II calvariae are from similar stratigraphic levels in Member I of the Kibish Formation. Based on (40)Ar/(39)Ar age measurements on alkali feldspar crystals from pumice clasts in the Nakaa'kire Tuff, a tuffaceous bed in Member I just below the hominin levels, we place an older limit of 198+/-14 ka (weighted mean age=196+/-2 ka) for the hominins. A younger limit of 104+/-7 ka (weighted mean age=104+/-1 ka) is provided by feldspars separated from pumice clasts in the Aliyo Tuff in Member III. Geological evidence indicates rapid deposition of each member of the Kibish Formation, concurrent with deposition of sapropels in the Mediterranean Sea. The (40)Ar/(39)Ar age measurements, together with correlations with sapropels, indicate that the hominin fossils are close in age to the older limit. Our preferred estimate of the age of the hominins is 195+/-5 ka, making them the earliest well-dated anatomically modern humans yet described.
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Age of the oldest known Homo sapiens from eastern Africa.
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January 2022
Department of Geography, University of Cambridge, Cambridge, UK.
Efforts to date the oldest modern human fossils in eastern Africa, from Omo-Kibish and Herto in Ethiopia, have drawn on a variety of chronometric evidence, including Ar/Ar ages of stratigraphically associated tuffs. The ages that are generally reported for these fossils are around 197 thousand years (kyr) for the Kibish Omo I, and around 160-155 kyr for the Herto hominins. However, the stratigraphic relationships and tephra correlations that underpin these estimates have been challenged.
View Article and Find Full Text PDFCorrelation of the KHS Tuff of the Kibish Formation to volcanic ash layers at other sites, and the age of early Homo sapiens (Omo I and Omo II).
J Hum Evol
October 2012
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112-0102, USA.
Hominin specimens Omo I and Omo II from Member I of the Kibish Formation, Ethiopia are attributed to early Homo sapiens, and an age near 196 ka has been suggested for them. The KHS Tuff, within Member II of the Kibish Formation has not been directly dated at the site, but it is believed to have been deposited at or near the time of formation of sapropel S6 in the Mediterranean Sea. Electron microprobe analyses suggest that the KHS Tuff correlates with the WAVT (Waidedo Vitric Tuff) at Herto, Gona, and Konso (sample TA-55), and with Unit D at Kulkuletti in the Ethiopian Rift Valley.
View Article and Find Full Text PDFGeochronology of the Turkana depression of northern Kenya and southern Ethiopia.
Evol Anthropol
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College of Mines, University of Utah, USA. [corrected].
Mesozoic and Cenozoic sedimentary rocks in the Turkana Depression of northern Kenya and southern Ethiopia rest on basement rocks that yield K/Ar cooling ages between 433 and 522 Ma. Proven Cretaceous strata are exposed in Lokitaung Gorge in northwest Kenya. Eocene basalts and rhyolites in Lokitaung Gorge, the Nabwal Hills, and at Kangamajoj, date between 34 and 36 Ma, recording the earliest volcanism in the region.
View Article and Find Full Text PDFIntrasite spatial variation of the Omo Kibish Middle Stone Age assemblages: artifact refitting and distribution patterns.
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Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Stony Brook, NY 11794-4364, USA.
The middle-late Pleistocene Kibish Formation of the Lower Omo Valley (Ethiopia) contains some of the oldest dated Homo sapiens fossils. Archaeological excavations at the Omo Kibish between 2002 and 2003 recovered numerous stone tools from extensive horizontal exposures of two sites, KHS (dated to 195+/-5 kyr) and BNS (dated to at least 104+/-7 kyr). Analysis of artifact distributions, lithic-debris densities, and refitting artifact sets sheds light on site-formation processes.
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September 2008
Department of Geology and Geophysics, 135 South 1460 East, Rm 209, University of Utah, Salt Lake City, UT 84112-0112, USA.
The Kibish Formation in southwestern Ethiopia, with an aggregate thickness of approximately 105 m, consists of lacustrine, marginal lacustrine, and deltaic deposits. It is divided into four members numbered I to IV on the basis of erosion surfaces (disconformities) between the strata of each member. It overlies the Mursi and Nkalabong formations, the latter of which is here shown to correlate with the Shungura Formation.
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