It's a shot of thirty millennia old.
One of the oldest Homo sapiens fossils found in Ethiopia is believed to be at least 230,000 years old.
A much higher age than estimated, according to a study which, once again, pushes back in time the beginnings of our species.
The remains of Omo Kibish 1 were unearthed in 1967 by the team of the famous Kenyan paleoanthropologist, Richard Leakey, recently deceased, in the lower Omo valley (southern Ethiopia), a prehistoric site world famous for its numerous fossils. hominids.
Although badly damaged, the body bones and skull fragments exhibited a surprisingly modern morphology, making Omo 1 the oldest known Homo sapiens fossil in East Africa.
And even throughout the African continent, before being dethroned by the discovery in 2017 of remains of primitive Homo sapiens in Morocco, dating back 300,000 years.
At Omo 1, very difficult to date in the absence of dentition, it was estimated to be approximately 130,000 years old.
A study published in 2005 then pushed back time to 195,000 years, based on analysis of the surrounding sediments - a much more reliable chronological marker in this case than direct dating on bones.
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But "there was still a lot of uncertainty about her age," explains Céline Vidal, lead author of a new study published Wednesday in the journal Nature.
This volcanologist from the University of Cambridge therefore left to re-excavate the Omo Kibish sedimentary basin, fed by the Kibish river.
Located in the Great Rift, the area was plagued by violent volcanic eruptions between 300,000 and 60,000 years BC.
Ashes as a chronological landmark
The ashes, projected for hundreds of kilometers around, have over time become inserted between the sediments deposited by the Kibish River.
Which, by lowering the level, gradually revealed the geological past, making Omo Kibish a real "library", according to Céline Vidal.
It is indeed thanks to the examination of these different layers that scientists have been able to assess the age of human remains - by a dating method, called "argon-argon", of the rare gases contained in the rocks.
In the early 2000s, the volcanic ash below the sediment containing the fossils was estimated to be around 195,000 years old.
This meant that Omo 1 was at most that age - "he could only be younger than the ash level below him," decrypts the volcanologist.
To be more precise, it would have been necessary to examine the thick layer of ash located above, necessarily deposited after.
“Alas, it was almost impossible as the ashes were fine, almost like flour,” she emphasizes.
These human remains could be even older
Thanks to more sophisticated methods, his team was able to examine the layer of ash covering the remains, and connect these volcanic deposits to a colossal explosion of the Shala volcano that occurred 233,000 years ago.
These analyzes made it possible to date the fossils of Omo under this layer, to approximately “233,000 - with a margin of error of 22,000 years”, details the study.
And this is a minimum age, that is, these human remains could be even older.
“It's a huge leap in time!
», Rejoices Aurélien Mounier, paleoanthropologist at the Musée de l'Homme, one of the authors.
And above all, the timescale is aligned more consistently with the latest models of human evolution, develops this CNRS researcher.
"We are getting closer to the date put forward by genetics, according to which it is around 300,000 years that modern man diverged from other human lineages."