Age of the oldest known Homo sapiens from eastern Africa

Abstract

Efforts to date the oldest modern human fossils in eastern Africa, from Omo-Kibish^1-3 and Herto^4,5 in Ethiopia, have drawn on a variety of chronometric evidence, including ⁴⁰Ar/³⁹Ar 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^3,6,7, and around 160-155 kyr for the Herto hominins^5,8. However, the stratigraphic relationships and tephra correlations that underpin these estimates have been challenged^6,8. Here we report geochemical analyses that link the Kamoya's Hominid Site (KHS) Tuff⁹, which conclusively overlies the member of the Omo-Kibish Formation that contains Omo I, with a major explosive eruption of Shala volcano in the Main Ethiopian Rift. By dating the proximal deposits of this eruption, we obtain a new minimum age for the Omo fossils of 233 ± 22 kyr. Contrary to previous arguments^6,8, we also show that the KHS Tuff does not correlate with another widespread tephra layer, the Waidedo Vitric Tuff, and therefore cannot anchor a minimum age for the Herto fossils. Shifting the age of the oldest known Homo sapiens fossils in eastern Africa to before around 200 thousand years ago is consistent with independent evidence for greater antiquity of the modern human lineage¹⁰.

Fig. 1. Late Middle Pleistocene tephrostratigraphy of the Main Ethiopian Rift.

a, Map of the MER showing silicic volcanoes and the late Middle Pleistocene sedimentary formations and relevant tephra units. White boxes with blue edges depict former correlatives of the KHS Tuff^, b, Synthetic stratigraphic logs of the late Middle Pleistocene formations showing former correlations for the Alyio Tuff (green), Konso SVT (pink, also identified in the Chew Bahir sediment core), new correlations for Konso unit TA-56 (yellow), and source eruptions (stars). LHM, lower Herto Member; UHM, upper Herto Member. c, Tephra ETH18-8 above the KHS Tuff at the KS locality in the Omo-Kibish Formation.

Fig. 2. Stratigraphy and age of the Shala Qi2 ignimbrite.

a, Location of site ETH17-14 near Lake Shala in the MER. b, Synthetic stratigraphy of the Qi2 ignimbrite of Shala at location ETH17-14. c, Photographs of units 14A, 14B and 14C of the Qi2 ignimbrite at site ETH17-14. Field observations indicate that deposits 14A and 14B are subunits of the same phase of the Qi2 eruption. d, ⁴⁰Ar/³⁹Ar age pooled data plotted on ideograms for samples 14A and 14C of the Qi2 ignimbrite (bottom) yielding a preferred composite eruption age of 233 ± 22 kyr (top). Data are weighted means. Error bars show data and results at 2σ. ⁴⁰Ar*, radiogenic ⁴⁰Ar; MSWD, mean square of weighted deviates; P, probability that residuals are explained by measurement errors exclusively; n, number of accepted grains.

Fig. 3. Geochemical fingerprints of MER tephra and their sources.

Major element abundances and trace element ratios of glasses from the Shala Qi2 ignimbrite (around 233 kyr), the Corbetti ignimbrite (around 177 kyr), the Gademotta unit D (around 184 kyr), the Kibish KHS and ETH18-8 tuffs, and the Konso TA-56 tuffs (all data from this study). Major element data are normalized to 100% anhydrous. Error bars shown are relative standard deviations derived from repeat measurements of matrix match glass secondary standards STH-S6 (for FeO*, n = 91; Supplementary Table 6) and ATHO-G (for Al₂O₃, CaO and TiO₂, n = 70; Supplementary Table 6). They are plotted in the top right corner of each plot for clarity and rescaled to the value of the centre point. In the case of element ratios, error propagation has been applied using analyses of standard ATHO-G (n = 15; Supplementary Table 7). Additional compositional observations and biplots are presented in Supplementary Fig. 5.