Earliest human remains in eastern Africa dated to more than 230,000 years ago

Ancient human fossils discovered in Ethiopia are much older than previously thought, experts claim, saying they could be as much as 230,000 years old. The remains – known as Omo I – were discovered in Ethiopia in the late 1960s, and are one of the oldest known examples of Homo sapiens fossils, with earlier attempts to date them placing them at just under 200,000 years old. However, a new study by the University of Cambridge found that the remains have to pre-date a colossal volcanic eruption in the area, which happened 230,000 years ago. 

To make the discovery the team dated the chemical fingerprints of volcanic ash layers, found above and below sediment where the fossils were discovered. 

The team said that while this pushes the minimum age for Homo sapiens in eastern Africa back by 30,000 years, future studies may extend the age even further. In 2017, archaeologists announced the discovery of the world’s oldest Homo sapiens fossils — a 300,000-year-old skull at Jebel Irhoud in Morocco. 

To date, the volcanic remains, the team collected pumice rock samples from the volcanic deposits and ground them down to sub-millimetre size. Scientists have been trying to precisely date the oldest fossils in eastern Africa, widely recognised as representing our species, Homo sapiens, ever since they were discovered in the 1960s. Earlier attempts to date them suggested they were less than 200,000 years old.  The Omo I remains were found in the Omo Kibish Formation in southwestern Ethiopia, which sits within the East African Rift valley.  The region is an area of high volcanic activity and a rich source of early human remains and artefacts.

By dating layers of volcanic ash above and below where fossil materials are found, scientists identified Omo I as one of the earliest examples of our species ever 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, the paper’s lead author. 

‘The fossils were found in a sequence, below a thick layer of volcanic ash that nobody had managed to date because the ash is too fine-grained.’

The four-year project, led by British volcanologist Professor Clive Oppenheimer. is attempting to date all major volcanic eruptions in the Ethiopian Rift. Each eruption has its own fingerprint – its own evolutionary story below the surface, which is determined by the pathway the magma followed,’ said Dr Vidal. 

‘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.’

The researchers carried out a geochemical analysis on the crushed rock to link the fingerprint of the volcanic ash, from the Kamoya Hominin Site, with an eruption of Shala volcano.  The team then dated pumice samples from the volcano, 250 miles from the site the human remains were discovered, to 230,000 years ago.  Since the Omo I fossils was found deeper than this particular ash layer, they must be more than 230,000 years old, the team explained.

‘First I found there was a geochemical match, but we didn’t have the age of the Shala eruption,’ said Vidal.

‘I immediately sent the samples of Shala volcano to our colleagues in Glasgow so they could measure the age of the rocks. 

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. Professor Asfawossen Asrat, a co-author of the study from Addis Ababa University in Ethiopia, said: ‘The Omo Kibish Formation is an extensive sedimentary deposit which has been barely accessed and investigated in the past. 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.

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, according to co-author Dr Aurélien Mounier, from the Musée de l’Homme in Paris.

He gave the example of a ‘tall and globular cranial vault and a chin’, before claiming that the new date estimate made the remains ‘the oldest unchallenged Homo sapiens in Africa. Until the Jebel Irhous discovery four years ago, most researchers believed that all humans living today descended from a population that lived in East Africa around 200,000 years ago. 

‘We can only date humanity based on the fossils that we have, so it’s impossible to say that this is the definitive age of our species,’ said 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. It’s probably no coincidence that 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,’ said Oppenheimer. 

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. 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,’ said co-author Professor Christine Lane, head of the Cambridge Tephra Laboratory. 

It’s possible that new finds and new studies may extend the age of our species even further back in time. There are many other ash layers we are trying to correlate with eruptions of the Ethiopian Rift and ash deposits from other sedimentary formations,’ said Vidal. ‘In time, we hope to better constrain the age of other fossils in the region.’

The findings have been published in the journal Nature.