Dating of massive volcanic eruption reveals ‘undisputed’ oldest modern human was already in East Africa 230,000 years ago
What was believed to be known about the origins of our own species was turned upside down in 2017 when, surprisingly, an international team announced the discovery in Morocco of the fossil remains of five Homo sapiens from between 300,000 and 350,000 years ago. The discovery placed our appearance a hundred thousand years earlier than previously believed and also in an unexpected place. Until then, the sapiens fossils from the Omo Kibish site, within the Rift Valley, in Ethiopia, 195,000 years old, were considered the oldest safely dated. And most paleontologists believed that all modern humans came from a single population that lived in East Africa. The ‘cradle’ changed (or there was more than one) and times changed, opening an unprecedented debate in the history of human evolution.
Now, a new study led by the University of Cambridge, England, has reassessed the age of the Ethiopian remains, known as Omo I, concluding that they must be older than a colossal volcanic eruption. that occurred 230,000 years ago and are therefore at least 35,000 years older than previously believed. They are still not as old as the Moroccan skull, jaw, and other bones but the researchers are convinced that theirs are “indisputable”, it is a full-fledged sapiens, while the Moroccans may belong to the early stages of our lineage, being the result of crossbreeding with other ancient human species in which the traits of our own have prevailed without subsequently prospering. Without going into those discussions, the results, published in the journal ‘Nature‘, reinforce the idea that modern humans, with the anatomical characteristics we now have, have been in the world longer than previously thought.
The remains, known as Omo I, were found in the late 1960s, and scientists have been trying to precisely date them ever since, using the chemical fingerprints of layers of volcanic ash above and below the rocks. sediments in which they appeared. So they identified them as the earliest evidence of our species.
“Using these methods, the generally accepted age of the Omo fossils is less than 200,000 years, but there has been a lot of uncertainty around this date,” says Céline Vidal of the Cambridge Department of Geography and lead author of the new paper. “The fossils were found under a thick layer of volcanic ash that no one had been able to date using radiometric techniques because the ash is too fine-grained,” she explains.
Volcanic deposits
As part of a four-year project, Vidal and his colleagues attempted to date all the major volcanic eruptions in the Ethiopian Rift to the time of the appearance of sapiens, a period known as the late Middle Pleistocene.
The researchers collected pumice stone samples from volcanic deposits and ground them down to submillimeter size. “Each eruption has its own fingerprint, its own evolutionary history below the surface, which is determined by the path that the magma followed,” says Vidal. “Once you’ve crushed the rock, you release the minerals in it and then you can date them and identify the chemical signature of the volcanic glass that holds the minerals together,” he adds.
The researchers carried out a new geochemical analysis to link the fingerprint of the thick layer of volcanic ash from the Kamoya Hominin Site (KHS ash) to an eruption of the Shala volcano, more than 400 kilometers away. The team then dated pumice stone samples from the volcano to 230,000 years ago. Since the Omo I fossils were found deeper than this particular ash layer, they must be more than 230,000 years old. “When I received the results (from the analysis of the samples) and discovered that the oldest Homo sapiens in the region was older than previously assumed, I was very excited,” acknowledges the researcher.
“Unequivocal characteristics”
According to Aurélien Mounier of the Musée du Man in Paris, unlike other fossils from the Middle Pleistocene that are believed to belong to the earliest stages of the Sapiens lineage, Omo I has “unmistakable modern human characteristics, such as a high cranial vault and globular and a chin. In his opinion, the new estimated date, de facto, makes him the “undisputed” oldest Homo sapiens in Africa.
The researchers say that while this study shows a new minimum age for Homo sapiens in East Africa, it is possible that new findings and new studies will push the age of our species even further back in time.
“We can only date humanity based on the fossils we have, so it is impossible to say that this is the definitive age of our species,” says Vidal. “The study of human evolution is always on the move: boundaries and timelines are changing as our understanding improves. But these fossils show how resilient humans are: that we survived, thrived, and migrated in an area that was so prone to natural disasters,” he says.
Cognitive abilities
It is probably no coincidence that our earliest ancestors lived in a geologically active valley: “It collected rain in lakes, provided fresh water and attracted animals, and served as a natural migration corridor stretching thousands of miles,” describes Clive Oppenheimer, director of the project that dates the volcanic eruptions. At the same time, volcanoes provided “fantastic materials to make stone tools, and from time to time we had to develop our cognitive skills when large eruptions transformed the landscape.”
“Our forensic approach provides a new minimum age for Homo sapiens in East Africa, but the challenge remains to provide a limit, a maximum age, for their emergence, which is widely believed to have taken place in this region,” he says. Christine Lane of Cambridge and co-author of the study. “It is possible that new findings and new studies will extend the age of our species even further back in time.” Which fossil will take the crown of the oldest sapiens remains to be seen.
