Dawn of humanity is pushed back to at least 230,000 years ago by University of Cambridge-led study
The dawn of our species has been pushed back in time after the earliest human remains in eastern Africa were dated to more than 230,000 years ago.
The research by an international team led by University of Cambridge scientists has revealed that Homo sapiens were around at least 30,000 years earlier than we thought.
The discovery follows the dating of a massive volcanic eruption in Ethiopia, which has helped scientists to understand more about Omo 1 – remains of the oldest fossils recognised as representing our species. Found in Omo Kibish Formation in south-western Ethiopia, within the East African Rift valley in the late 1960s, efforts to date Omo 1 have been going on ever since by exploring the chemical fingerprints of volcanic ash layers above and below the sediments in which the fossils were found.
“Using these methods, the generally accepted age of the Omo fossils is under 200,000 years, but there’s been a lot of uncertainty around this date,” said Dr Céline Vidal, from Cambridge’s Department of Geography, and lead author a paper published in Nature.
“The fossils were found in a sequence, below a thick layer of volcanic ash that nobody had managed to date with radiometric techniques because the ash is too fine-grained.”
Dr Vidal and colleagues have been working on a four-year project led by Professor Clive Oppenheimer to date all the major volcanic eruptions in the Ethiopian Rift around the time Homo sapiens emerged, a period known as the late Middle Pleistocene. They collected pumice rock samples from the volcanic deposits and ground them down to sub-millimetre size.
Dr Vidal explained: “Each eruption has its own fingerprint – its own evolutionary story below the surface, which is determined by the pathway the magma followed. Once you’ve crushed the rock, you free the minerals within, and then you can date them, and identify the chemical signature of the volcanic glass that holds the minerals together.”
New geochemical analysis then linked the fingerprint of the thick volcanic ash layer from the Kamoya Hominin Site (KHS) with an eruption of Shala volcano, more than 400km away.
“First I found there was a geochemical match, but we didn’t have the age of the Shala eruption,” said Dr Vidal.
Pumice samples were sent to Dr Dan Barfod and Professor Darren Mark at the Scottish Universities Environmental Research Centre (SUERC) in Glasgow to measure the age of the rocks.
They dated them to 230,000 years ago and since the Omo I fossils were found deeper than this ash layer, they must be more than 230,000 years old.
“When I received the results and found out that the oldest Homo sapiens from the region was older than previously assumed, I was really excited,” said Dr Vidal.
Co-author Prof Asfawossen Asrat, from Addis Ababa University in Ethiopia, who is currently based at BIUST in Botswana, was co-leader of the investigation in the field.
“The Omo Kibish Formation is an extensive sedimentary deposit which has been barely accessed and investigated in the past,” said Prof Asrat. “Our closer look into the stratigraphy of the Omo Kibish Formation, particularly the ash layers, allowed us to push the age of the oldest Homo sapiens in the region to at least 230,000 years.”
Dr Aurélien Mounier, another co-author, from the Musée de l’Homme in Paris, added: “Unlike other Middle Pleistocene fossils which are thought to belong to the early stages of the Homo sapiens lineage, Omo I possesses unequivocal modern human characteristics, such as a tall and globular cranial vault and a chin. The new date estimate, de facto, makes it the oldest unchallenged Homo sapiens in Africa.”
Further finds could yet age the species even more.
“We can only date humanity based on the fossils we have, so it’s impossible to say this is the definitive age of our species,” said Dr Vidal. “The study of human evolution is always in motion: boundaries and timelines change as our understanding improves. But these fossils show just how resilient humans are: that we survived, thrived and migrated in an area that was so prone to natural disasters.”
Prof Oppenheimer said: “It’s probably no coincidence our earliest ancestors lived in such a geologically active rift valley – it collected rainfall in lakes, providing fresh water and attracting animals, and served as a natural migration corridor stretching thousands of kilometres.
“The 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.”
Co-author Prof Christine Lane, head of the Cambridge Tephra Laboratory where much of the work was carried out, added: “Our forensic approach provides a new minimum age for Homo sapiens in eastern Africa, but the challenge still remains to provide a cap, a maximum age, for their emergence, which is widely believed to have taken place in this region.
“It’s possible that new finds and new studies may extend the age of our species even further back in time.”
Dr Vidal, a fellow of Fitzwilliam College, noted: “There are many other ash layers we are trying to correlate with eruptions of the Ethiopian Rift and ash deposits from other sedimentary formations, In time, we hope to better constrain the age of other fossils in the region.”
The research was supported in part by the Leverhulme Trust, the Cambridge-Africa ALBORADA Research Fund and the Natural Environment Research Council and the National Environmental Isotope Facility.
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