About 74,000 years ago, Mount Toba in Sumatra experienced a super eruption, one of the largest in Earth's history, potentially causing a massive disruption to the world's climate.
Some scientists have suspected that a volcanic winter resulting from the eruption was a shift large enough to wipe out most early humans, due to genetic evidence suggesting that the human population declined sharply. But now a groundbreaking study of an archaeological site in northwestern Ethiopia once inhabited by early modern humans has added to a growing body of evidence suggesting the event may not have been so apocalyptic.
Instead, the new research found people at that location, known as Shinfa-Metema 1, adapted to the arid conditions caused by the volcanic eruption in a way that may have facilitated humanity's crucial migration from Africa to the rest of the world.
Microscopic fragments of volcanic glass found alongside stone tools and animal remains in the same layer of sediment at the Shinfa-Metema 1 site, near the Shinfa River in Ethiopia, show that people occupied the site before and after the volcano erupted more than 6,000 kilometers away erupted.
"These fragments are smaller than the diameter of a human hair. Even as small as that, they are still large enough to analyze the chemistry and trace elements," said John Kappelman, professor of anthropology and geological sciences at the University of Texas at Austin and lead author of the study, which was published Wednesday. in the journal Nature.
By piecing together clues from the fossils and artifacts found at the site, along with geological and molecular analyses, the team began to understand how the people who lived there progressed despite the likely climate change brought on by the volcanic catastrophe.
Catching fish
To understand the climate around the time of the eruption, Kappelman and his colleagues analyzed oxygen and carbon isotopes, variations of the same element, from ostrich eggshells and fossilized mammal teeth. That work shed light on water intake and revealed that the animals ate plants that were more likely to grow in drier conditions.
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"The isotopes are incorporated into the hard tissues. So in the mammals we look at their teeth, the enamel of their teeth, but we also find it in the eggshell of the ostrich," he said.
An analysis of the site's flora and fauna also revealed an abundance of fish remains in the aftermath of the eruption. The finding may not be surprising given the site's proximity to the river, but fish are rare at other Stone Age sites from the same period, the study said.
"People start to increase the percentage of fish in the diet as Toba comes in. They catch and process almost four times as many fish (as before the eruption)," he said.
"We think the reason for this is that if Toba actually creates more drought, it means it will be a shorter wet season, which means a longer dry season."
The team theorized that the drier climate, counterintuitively, explains the increased reliance on fish: as the river shrank, fish became trapped in waterholes or shallower streams that hunters could more easily target.
Blue versus green corridor
The fish-rich waterholes may have created what the team described as a "blue corridor," along which early humans moved north from Africa when fish were no longer available. This theory contradicts most other models that suggest that humanity's main migration out of Africa took place along "green corridors" during humid periods.
"This study demonstrates the great plasticity of Homo sapiens populations and their ability to adapt easily to any type of environment, whether hyper-humid or hyper-arid, including during catastrophic events such as the hyper-explosion of the Toba volcano," said Ludovic Slimak, researcher at the French National Center for Scientific Research and the University of Toulouse, in an email. Slimak was not involved in the investigation.
The study authors were also able to examine the geology of the ancient riverbed, which suggested that it flowed slower and lower at that point than in the present.
"We can do that just by looking at the cobblestones," Kappelman said. "A very energetic river can move larger boulders and cobbles than a river that is not as (energetic). What we find for the ancestral river is smaller than today's river."
Oldest known arrowheads?
The researchers also discovered the remains of several small triangular points, which are tantalizingly among the earliest examples of archery use and provide clues that the site's inhabitants may have used bows and arrows to hunt fish and other larger prey .
Slimak, who has studied similar points discovered in France that date back 50,000 years, agreed with the new study's assessment of the artifacts.
"The authors also highlight very clear indicators pointing to the existence of archery here 74,000 years ago," Slimak said. "There is therefore every reason to ... regard these ancient Homo sapiens as bearers of already highly advanced technologies, largely emancipated from natural and climatic limitations, crucial factors for understanding their migrations later, across all continents and under all latitudes."
Ancient human species likely left Africa several times, but archaeologists and geneticists largely agree that the main dispersal of Homo sapiens, our own species - which eventually led to modern humans living in all corners of the world - was about 70,000 to took place 50,000 years ago. past.
The new research offers another potential scenario for how this spread occurred, without ruling out previous theories, said Chris Stringer, professor and research leader in human evolution at the Natural History Museum in London, who called it an "intriguing paper."
"I am sure that each of these propositions will stimulate debate among the relevant specialists, but I think the authors have made a plausible (though not definitive) case for each scenario they propose," Stringer said via email .
"Of course, this new work does not mean that moist corridors were not still important channels for dispersal from Africa, but this work adds credible additional possibilities during more dry phases."
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