The remains of Omo I have been found in the Omo Kibish Formation in southwestern Ethiopia, in the East African Rift Valley. The area is an area of ​​high volcanic activity and a rich source of ancient human remains and artifacts such as stone tools. By dating the volcanic ash layers above and below where the archaeological and fossil materials are, scientists have identified Omo I as the first evidence of our species. A wise man

Dr Céline Vidal from the Cambridge Department of Geography, lead author of the article, said: “Using these methods, the generally accepted age for Omo fossils is less than 200,000 years, but there has been a lot of uncertainty around that date. “The fossils were found sequentially, under a thick layer of volcanic ash that no one has been able to date with radiometric techniques because the ash is very fine grained.”

Researchers from the Omo-Kepish geological formation in southwestern Ethiopia. credit: dino

as part of a Four-year project Led by Professor Cliff Oppenheimer, Vidal and colleagues attempted to date all major volcanic eruptions in the Ethiopian Rift to the time of the emergence of sane man, a period known as the Upper Middle Ice Age.

The researchers collected samples of pumice from volcanic sediments and crushed them to less than a millimeter in size. “Each eruption has its own fingerprints, its evolutionary history beneath the surface, which is determined by the path taken by the magma,” Vidal said. “Once you’ve cracked the rock, you’re releasing the minerals inside, and then you can date it and determine the chemical signature of the volcanic glass that holds the minerals together.”

Researchers have conducted a new geochemical analysis to correlate the trail of the thicker layer of volcanic ash from the Kamoya Hominin (KHS) site with the eruption of the Shala volcano, more than 400 kilometers away. The team then dated the pumice samples from the volcano 230,000 years ago. Since the Omo I fossils were found much deeper than this ash layer, they must be more than 230,000 years old.

Omo-Kepish Formation in southwestern Ethiopia. Credit: Celine Vidal

“I first discovered that there is a geochemical match, but we weren’t as old as the Shalla eruption,” Vidal said. The samples were sent to co-authors Dr Dan Barford and Professor Darren Mark, Scottish Universities Environmental Research Center (SUERC) in Glasgow, so they could measure the age of the rocks.

“When I received the results and discovered that the greatest sane man In the area where he was older than he thought, he was very excited.”

“The Omo-Kepish Formation is a large sedimentary deposit that was barely accessed and studied in the past,” said co-author and co-leader of the field study, Professor Asfausen Asrat from Addis Ababa University in Ethiopia. at BIUST University in Botswana. “Our more detailed examination of the Earth’s layers of the Omo-Kepish Formation, particularly the ash layers, has allowed us to go back on the age of the oldest formation. sane man In the region for at least 230 thousand years.

Unlike other fossils from the Middle Pleistocene that belong to the early stages of sane man Co-author Dr. Aurélien Mounier of the Musée de l’Homme in Paris, the Omo I possessed unmistakable modern human characteristics, such as the dome of the long, spherical skull and chin. «The new estimated date, de facto, in fact, the oldest undisputed sane man and Africa.

Reproduction of the skull of Omo-Kebech, Museum of Noir Civilizations in Dakar (Senegal). credit: GuillaumeG

The researchers say that although this study shows a lower limit for a new age, sane man In East Africa, new discoveries and new studies could turn the era of our species back.

“We can only determine the history of mankind based on the fossils we have, so it is impossible to say that this is the last age of our species,” Vidal said. “The study of human evolution is always on the move: boundaries and time frames change as our understanding improves. But these fossils show how resilient humans are: we have survived, thrived and migrated to an area that was very prone to natural disasters.”

“Perhaps it is no coincidence that our early ancestors lived in such a geologically active rift valley: it collected rain in lakes, provided fresh water and attracted animals, and served as a natural migration corridor stretching for thousands of miles,” said Oppenheimer. stony, and from time to time we had to develop our cognitive skills when big eruptions changed the landscape. «

Our forensic approach sets a new minimum age for sane man In East Africa, but the challenge remains to provide a ceiling, an upper age limit, for their occurrence, which is widely believed to have occurred in this region,” said co-author Professor Christine Lane, director of the Cambridge Tephra Laboratory, where there is a lot of work. It is possible that new discoveries and new studies could turn the lives of our species back in time.”

“There are many other ash layers that we’re trying to associate with Ethiopian rift eruptions and ash deposits from other sedimentary formations,” Vidal said. “Over time, we hope to better reduce the age of other fossils in the area.”

Reference: “Age of the Oldest Homo sapiens known in East Africa” by Céline M. Vidal, Christine S. Lynn, Asfousen Asrat, Dan in Barfod, Darren F. Mark, Emma L. Tomlinson, AmiMichael Zavo Tadesse, Jizahijn Yergo, Alain Dino, William Hutchison, Aurelien Meunier and Cliff Oppenheimer , January 12, 2022, nature.
DOI: 10.1038 / s41586-021-04275-8

The research was supported in part by the Leverhulme Trust, the Cambridge-Africa ALBORADA Research Fund, the Natural Environment Research Council and the National Environmental Isotope Facility. Céline Vidal is a Fellow at Fitzwilliam College, Cambridge.