CAMBRIDGE, England — The oldest remains of a modern human have been backdated 30,000 years earlier than previously thought, to 230,000 years ago. The fossils – known as Omo I – were found in Ethiopia in 1967 by a team directed by leading anthropologist Richard Leakey, who died on January 2 at the age of 77.
Scientists have been attempting to date the oldest fossils in eastern Africa widely recognized as representing our species, Homo sapiens, precisely ever since. Now, the international team, led by University of Cambridge scientists, has established that they are much older than previously thought by dating the chemical fingerprints of volcanic ash layers found above and below the sediments in which the fossils were found.
Earlier attempts to date the fossils suggested they were less than 200,000 years old. The new research, published in the journal Nature, shows they must be older than a “colossal” volcanic eruption that took place 230,000 years ago.
The Omo I remains were found in the Omo Kibish Formation in south western Ethiopia, within the East African Rift valley. It is an area of high volcanic activity, and a rich source of early human remains and artifacts including stone tools.
By dating the layers of volcanic ash above and below where archaeological and fossil materials are found, 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 under 200,000 years, but there’s been a lot of uncertainty around this date,” says study lead author Dr Céline Vidal, from Cambridge’s Department of Geography,” in a statement. “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.”
Linking our history to volcanic eruptions
As part of a four-year project led by Professor Clive Oppenheimer, Dr Vidal and her colleagues have been attempting to date all the major volcanic eruptions in the Ethiopian Rift around the time of the emergence of Homo sapiens, a period known as the late Middle Pleistocene.
The team collected pumice rock samples from the volcanic deposits and ground them down to sub-millimeter size. “Each eruption has its own fingerprint – its own evolutionary story below the surface, which is determined by the pathway the magma followed,” says 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 new geochemical analysis to link the fingerprint of the thick volcanic ash layer from the Kamoya Hominin Site (KHS ash) with an eruption of Shala volcano, more than 250 miles away.
The team then dated pumice samples from the volcano to 230,000 years ago. Since the Omo I fossils were found deeper than that particular ash layer, they must be more than 230,000 years old.
“First I found there was a geochemical match, but we didn’t have the age of the Shala eruption,” says 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.”
“The Omo Kibish Formation is an extensive sedimentary deposit which has been barely accessed and investigated in the past,” says study co-author Professor Asfawossen Asrat, of Addis Ababa University in Ethiopia. “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.”
Adds co-author Dr. Aurélien Mounier, of France’s Musée de l’Homme: “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.”
‘These fossils show just how resilient humans are’
The researchers say that while the study shows a new minimum age for Homo sapiens in eastern Africa, it’s possible that new finds and new studies may extend the age of our species even further back in time.
“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. The study of human evolution is always in motion: boundaries and timelines change as our understanding improves,” says Vidal. “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 kilometers,” notes Prof. 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,” concludes co-author Christine Lane, head of the Cambridge Tephra Laboratory where much of the work was carried out. “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.”
South West News Service writer Stephen Beech contributed to this report.