The age of the oldest fossils widely recognized as representatives of our species, Homo sapiens, has long been uncertain.
Now, the dating of a huge volcanic eruption in Ethiopia reveals that they are much older than previously thought. Specifically, it is estimated that the oldest human remains in East Africa are dated more than 230,000 years ago, according to the researchers published in the journal ‘Nature’.
The remains – known as Omo I – were found in Ethiopia in the late 1960s, and scientists have tried to accurately date them ever since, using chemical fingerprints from layers of volcanic ash found above and below the sediments in which the fossils were found.
An international team of scientists, led by the University of Cambridge, in the United Kingdom, has reassessed the age of the remains of Omo I and Homo sapiens as a species. Previous attempts to date the fossils suggested they were less than 200,000 years old, but new research shows that they must be older than a colossal volcanic eruption that took place 230,000 years ago.
The remains of the Omo I were found in the Omo Kibish Formation, in southwestern Ethiopia, within the Rift Valley of East Africa. The region is an area of great volcanic activity and a rich source of early human remains and artifacts such as stone tools.
By dating the volcanic ash layers found above and below archaeological and fossil materials, scientists identified Omo I as the earliest evidence of our species, Homo sapiens.
“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 in a statement Dr. Céline Vidal, from the Cambridge Department of Geography, main author of the work. “The fossils were found in a sequence, under a thick layer of volcanic ash that nobody had managed to date with radiometric techniques because the ash is too fine-grained.”
As part of a four-year project led by Professor Clive Oppenheimer, Vidal and his colleagues have attempted to date all major volcanic eruptions in the Ethiopian Rift around the time of the appearance of Homo sapiens, a period known as the late Middle Pleistocene. .
The researchers collected pumice rock samples from volcanic deposits and ground them down to sub-millimeter size. “Each eruption has its own fingerprint, its own evolutionary history under the surface, which is determined by the path that the magma followed”, Vidal points out. “Once the rock has been crushed, the minerals within it are released, and then you can date them, and identify the chemical signature of the volcanic glass that holds the minerals together.”
The researchers carried out new geochemical analyzes to link the fingerprint of the thick layer of volcanic ash from the Kamoya Hominid Site (KHS ash) to an eruption of the Shala volcano, more than 400 kilometers away.
The team then dated pumice samples from the volcano to 230,000 years old. Since the Omo I fossils were found deeper than this particular ash layer, they must be more than 230,000 years old.
“I first discovered that there was a geochemical match, but we were not as old as the Shala eruption,” remember. “I immediately sent the Shala volcano samples to our colleagues in Glasgow to measure the age of the rocks. When I received the results and discovered that the oldest Homo sapiens in the region was older than expected, I was very excited “, he points out.
“The Omo Kibish Formation is an extensive sedimentary deposit that has hardly been accessed and investigated in the past,” adds co-author and co-director of the field research, Professor Asfawossen Asrat, from Addis Ababa University (Ethiopia), who is currently at BIUST in Botswana. “Our more detailed examination of the stratigraphy of the Omo Kibish Formation, particularly the ash layers, allowed us to raise the age of the oldest Homo sapiens in the region to at least 230,000 years.”
“Unlike other Middle Pleistocene fossils believed to belong to the early stages of the Homo sapiens lineage, Omo I possesses unmistakable modern human characteristics, such as a tall, globular cranial vault and chin,” underlines the co-author, Dr. Aurélien Mounier, from the Musée de l’Homme in Paris. “The new estimate of the date, de facto, makes it the oldest Homo sapiens in Africa without question.”
The researchers say that although this study shows a new minimum age for Homo sapiens in East Africa, it is possible that new findings and new studies extend 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.” explains Vidal. “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 survive, thrive and migrate in an area so prone to natural disasters. “
“It is probably not a coincidence that our first ancestors lived in such a geologically active fissure valley: it collected rainfall in lakes, providing fresh water and attracting animals, and served as a natural migration corridor that stretched thousands of kilometers”, Oppenheimer highlights.
“Volcanoes provided fantastic materials for making stone tools, and from time to time we had to develop our cognitive skills when large eruptions transformed the landscape.”, Add.
“Our forensic approach provides a new minimum age for Homo sapiens in East Africa, but the challenge remains to provide a cap, a maximum age, for its occurrence, which is widely believed to have occurred in this region.” highlights the co-author, Professor Christine Lane, director of the Cambridge Tephra Laboratory, where much of the work was carried out. “It is possible that the new findings and new studies extend the age of our species even further back in time.”
“There are many other layers of ash that we are trying to correlate with the eruptions of the Ethiopian Rift and with the ash deposits of other sedimentary formations,” apostille Vidal. “Over time, we hope to better limit the age of other fossils in the region.”
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