Paper is public
https://www.nature.com/articles/s41586-021-04275-8.pdf
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 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, and around 160–155 kyr for the Herto hominins. However, the stratigraphic relationships and tephra correlations
that underpin these estimates have been challenged. 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, 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 lineage.
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