Human evolution is a complex story with many twists! How our ancestors diverged from other ape species, how they migrated to different parts of the globe, how they dominated so many ecosystems – the answers keep changing as science advances. Scientists continue to uncover exciting new information to help draw a concrete timeline of our history.
In the late 1960s, researchers unearthed one of these valuable pieces of the puzzle in Ethiopia. The remains, known as “Omo I”, have been considered one of the finest and oldest fossils belonging to our species –Homo sapiens.
Now, nearly five decades after the discovery, researchers have concluded that the fossils are at least 36,000 years older than previously thought!
The oldest remains of modern man
This oldest fossil comes from the Omo Kibish Formation in southwestern Ethiopia in the East African Rift Valley. This specific region of high volcanic activity has been of great importance as it is a rich source of ancient human remains and artifacts from that era, such as stone tools.
For years, scientists have used the chemical fingerprints of volcanic ash above and below the remains to estimate a potential depositional timeline for these fossils. Accurate dating of the remains of Omo I has been difficult, with earlier findings suggesting they were less than 200,000 years old, around 197,000 years old.
“The fossils were found in a sequence, under a thick layer of volcanic ash that no one had been able to date with radiometric techniques because the ash is too fine-grained,” said Céline Vidal from the University of Cambridge, who conducted the study.
It turns out that they are much older than previous estimates! Reassessment by the international team of scientists led by the University of Cambridge found that the human remains could be up to 233,000 years old, significantly altering the timeline.
The most recent findings are also consistent with most models of modern human evolution, which predict that Homo sapiens originated and diverged about 350,000 to 200,000 years ago.
Study volcanic ash
The new findings came to light through a dating of massive volcanic eruptions in Ethiopia to the late Middle Pleistocene, signifying the emergence of Homo sapiens. The team took samples of pumice rock from deposits at the site and ground them down to sub-millimeter size.
“Each eruption has its own fingerprint – its own evolutionary history below the surface, which is determined by the path taken by the magma. Once you crush the rock, you release the minerals inside, and then you can date and identify the chemical signature of the volcanic glass that holds the minerals together,” says Vidal.
Finally, the researchers carried out a new geochemical analysis to link the footprint of the site’s volcanic ash layer to the eruption of the Shala volcano. The team then dated samples from the volcano to 233,000 (±22,000) years ago, indicating the age of the Omo fossil.
“The study of human evolution is always on the move: boundaries and timelines change as our understanding improves. But these fossils show how resilient humans are: that we have survived, thrived and migrated in a region so prone to natural disasters,” concludes Vidal.
The team says further research could even push back the original date of our species’ arrival.
The results were published in the journal Nature last week and can be viewed here.
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