Earlier date for Ethiopian fossils highlights rise of Homo sapiens

By Will Dunham

(Reuters) – Volcanic ash left behind from a massive ancient eruption has helped scientists determine that important Homo sapiens fossils found in Ethiopia in 1967 are older than previously believed, offering new insight into the dawn of our species.

Researchers said on Wednesday they used geochemical imprints from a thick layer of ash found above sediment containing the fossils to verify that it was the result of an eruption that spat volcanic fallout over a large part of Ethiopia. about 233,000 years ago.

Because the fossils were located under this ash, they predate the eruption, the researchers said, although the number of years remains uncertain. It was previously believed that fossils were no more than 200,000 years old.

The fossils, called Omo I, were discovered in southwest Ethiopia in an area called the Omo Kibish geological formation during an expedition led by the late paleoanthropologist Richard Leakey. They include a fairly complete cranial vault and lower jaw, some vertebrae, and parts of the arms and legs.

Scientists have sought greater clarity on the chronology of our species’ origins in Africa.

The new findings are consistent with the most recent scientific models of human evolution, placing the emergence of Homo sapiens between 350,000 and 200,000 years ago, said University of Cambridge vulcanologist Celine Vidal , lead author of the study published in the journal Nature.

Research published in 2017 showed that the bones and teeth discovered at a site called Jebel Irhoud in Morocco were over 300,000 years old, representing the earliest fossils attributed to Homo sapiens. Some scientists have wondered if these fossils really belong to our species.

The remains of Jebel Irhoud “lack some of the key morphological characteristics that define our species. They particularly lack a high and globular cranial vault and a chin on the lower jaw, which can be observed on Omo I ”, declared the paleoanthropologist Aurélien Mounier of the CNRS and the Musée de l’Homme in Paris, co -author of the new study.

“Omo I is the oldest Homo sapiens with unmistakable modern human traits,” added Clive Oppenheimer, volcanologist and co-author of the Cambridge University study.

The volcanic ash layer defied previous efforts to calculate its age because its grains were too fine for scientific dating methods.

The researchers determined the geochemical composition of the ash and compared it with other volcanic remains in the area. They found it to correspond to a light, porous volcanic rock called a pumice stone created during the eruption of the Shala volcano about 230 miles (370 km). They were then able to date the pumice stone to determine when the rash occurred.

“I think it’s important to keep in mind that the study of human evolution is always on the move: boundaries and time frames change as our understanding improves,” Vidal said. “But these fossils show how resilient humans are – that we survived, prospered, and migrated to an area that was so prone to natural disasters.”

While the study has resolved the minimum age of the fossils, their maximum age remains a mystery. There is also a layer of ash under the sediment containing the fossils which has not yet been dated. This date would fix the maximum age of the fossils.

“It is probably no coincidence that our earliest ancestors lived in such a geologically active rift valley – it collected precipitation in lakes, providing fresh water and attracting animals, and served as a natural migration corridor. ‘stretching for thousands of miles,’ Vidal said. “Volcanoes provided fantastic materials for making stone tools, and every now and then we had to develop our cognitive skills when large eruptions transformed the landscape. “

(Reporting by Will Dunham in Washington; Editing by Lisa Shumaker)

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