Stratigraphic placement and age of modern humans from Kibish, Ethiopia (original) (raw)

Nature volume 433, pages 733–736 (2005)Cite this article

Abstract

In 1967 the Kibish Formation in southern Ethiopia yielded hominid cranial remains identified as early anatomically modern humans, assigned to Homo sapiens1,2,3,4. However, the provenance and age of the fossils have been much debated5,6. Here we confirm that the Omo I and Omo II hominid fossils are from similar stratigraphic levels in Member I of the Kibish Formation, despite the view that Omo I is more modern in appearance than Omo II1,2,3. 40Ar/39Ar ages on feldspar crystals from pumice clasts within a tuff in Member I below the hominid levels place an older limit of 198 ± 14 kyr (weighted mean age 196 ± 2 kyr) on the hominids. A younger age limit of 104 ± 7 kyr is provided by feldspars from pumice clasts in a Member III tuff. Geological evidence indicates rapid deposition of each member of the Kibish Formation. Isotopic ages on the Kibish Formation correspond to ages of Mediterranean sapropels, which reflect increased flow of the Nile River, and necessarily increased flow of the Omo River. Thus the 40Ar/39Ar age measurements, together with the sapropel correlations, indicate that the hominid fossils have an age close to the older limit. Our preferred estimate of the age of the Kibish hominids is 195 ± 5 kyr, making them the earliest well-dated anatomically modern humans yet described.

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Acknowledgements

We thank J. Mya, R. Maier and X. Zhang for technical support for the geochronology; participants in the Kibish expeditions between 1999 and 2003, including Z. Assefa, J. Shea, S. Yirga, J. Trapani and especially C. Feibel, B. Passey and C. Fuller for their geological contributions; and R. Leakey, K. Butzer and especially P. Abell for providing us with information and documents about the 1967 expedition to the Kibish area. We thank the Government of Ethiopia, the Ministry of Youth, Sports and Culture, the Authority for Research and Conservation of Cultural Heritage, and the National Museum of Ethiopia for permission to study the Kibish Formation. Support was provided by the National Science Foundation, the Leakey Foundation, the National Geographic Society and the Australian National University. Neutron irradiations were facilitated by the Australian Institute of Nuclear Science and Engineering and the Australian Nuclear Science and Technology Organization.

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Authors and Affiliations

  1. Research School of Earth Sciences, Australian National University, Canberra, ACT, 0200, Australia
    Ian McDougall
  2. Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112, USA
    Francis H. Brown
  3. Department of Anatomical Science, Stony Brook University, Stony Brook, New York, 11794, USA
    John G. Fleagle

Authors

  1. Ian McDougall
  2. Francis H. Brown
  3. John G. Fleagle

Corresponding author

Correspondence toIan McDougall.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Table 1

Electron Microprobe analysis of glass from tuffs and pumice of the Kibish Formation. (XLS 22 kb)

Supplementary Table 2

Results of laser fusion 40Ar/39Ar dating of alkali feldspar crystals from two pumice clasts (mass ~5 g) from Member I, Kibish Formation, west of Omo River at Nakaa'kire, 1 km north of Aliyo, Ethiopia (5°24.59'N, 35°54.52'E). (DOC 50 kb)

Supplementary Table 3

Results of laser fusion 40Ar/39Ar dating of alkali feldspar crystals from three pumice clasts in a tuff of Member I, Kibish Formation, west of Omo River at Nakaa'kire, near Omo II site, Ethiopia (5°24.6'N, 35°54.5'E). (DOC 87 kb)

Supplementary Table 4

Results of laser fusion 40Ar/39Ar dating of alkali feldspar crystals from two pumice casts, 99-275A, B, from pumiceous gravels, 0.4 km SSE of KHS, and from two pumice clasts 99-274A, B, 0.5 km SE of KHS, all from Member III, Kibish Formation, Ethiopia. (DOC 145 kb)

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McDougall, I., Brown, F. & Fleagle, J. Stratigraphic placement and age of modern humans from Kibish, Ethiopia.Nature 433, 733–736 (2005). https://doi.org/10.1038/nature03258

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Editorial Summary

The earliest humans just got earlier

Thirty-five years ago, papers in Nature by Richard Leakey and colleagues described fossils from the Kibish Formation, southern Ethiopia, attributed to Homo sapiens. These fossils are important to hypotheses concerning our African ancestry, and were believed to be about 130,000 years old. Recent finds from Herto, also in Ethiopia, put the date of the earliest modern humans back to around 160,000 years ago. But now a reappraisal of the Kibish sediments suggests that they are much older than was thought, putting the date of the human remains back to 195,000 years ago.

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