by Age of the oldest known Homo sapiens from eastern Africa
Efforts to date the oldest modern human fossils in eastern Africa, from Omo-Kibish1,2,3 and Herto4,5 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 I3,6,7, and around 160–155 kyr for the Herto hominins5,8. However, the stratigraphic relationships and tephra correlations that underpin these estimates have been challenged6,8. 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 arguments6,8, 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.
This is a complicated one to explain as there are widely published fossils dated either much earlier or later, but this data continues to narrow the band down further.
The problem, of course, is that this is a How Long is a Piece of String question, complicated by how accurately we expect that measurement to be: even if we just assume the dating is perfectly accurate (while recalling there's a multi tens of thousands of years for margin of error), we still have to decide whether this suite of traits represents an anatomically modern human according to metrics that kind of have to generally be implicitly agreed upon by independent research institutes all over the place without necessarily ever actually outright stating they agree, and just as importantly, all sort of agree that X fossil does meet that criteria, while Y doesn't. This is far from easy!
But the more measurements that come in somewhere in the middle of those approximate extremities, the more likely we're representing the data best or most conservatively by plopping down somewhere in the middle. Accordingly, at present it is I believe correct to say that anatomically modern humans arrived on this planet around 220,000 years ago, give or take 30,000 years or so.
