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About 74,000 years ago, a massive eruption occurred in Mount Toba in Sumatra, one of the largest in Earth’s history, which could have caused a huge impact on the world’s climate.
Some scientists doubt that the volcanic winter resulting from the eruption was a change big enough to wipe out most early humans because of genetic evidence that suggests a sharp decline in the human population. But now a ground-breaking study of an archaeological site in northwestern Ethiopia once occupied by early modern humans has added to a growing body of evidence that suggests the event may not have been so apocalyptic after all. .
Instead, the new research found that people at that site, known as Shinfa-Metema 1, had adapted to the high conditions brought about by the volcanic eruption in a way that facilitated humanity’s vital migration out of Africa to the rest of the world.
Microscopic fragments of volcanic glass found alongside stone tools and animal remains in the same layer of sediments at the Shinfa-Metema 1 site, near Ethiopia’s Shinfa River, show human occupation of the site before and after the larger eruption than 4,000 miles away.
“These fragments are smaller than the diameter of a human hair. Even as small as (that) they’re still big enough to analyze the chemistry and trace elements,” said John Kappelman, professor of anthropology and geological science at the University of Texas at Austin and lead author of the study, who published on Wednesday. in the journal Nature.
By piecing together clues from the fossils and artefacts found at the site, as well as geological and molecular analysis, the team began to understand how the people who lived there survived despite likely climate change triggered the volcanic cataclysm.
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 showed that the animals ate plants that were more likely to grow in drier conditions.
“The isotopes are incorporated into the hard tissues. So for the mammals, we look at their teeth, their tooth enamel, but we also find it in the ostrich eggshell,” he said.
An analysis of the site’s flora and fauna also revealed an abundance of fish remains after the eruption. The finding may not be surprising given the site’s proximity to the river, but other Stone Age sites from the same period rarely contain fish, the study noted.
“People start increasing the percentage of fish in the diet when Toba comes in. They are catching and processing almost four times more fish (as before the eruption),” he said.
“We think the reason for that is that if Toba is actually experiencing more aridity, that means it’s going to 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 receded, fish were trapped in shallower waterholes or streams that hunters could more easily target. easy.
Blue vs. green trail
The fish-rich waterholes may have created what the team described as a “blue corridor,” where early humans moved north out of Africa when they had exhausted the fish. This theory contradicts most other models which suggest that the main migration of humanity 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 easily adapt to any type of environment, whether hyper-humid or hyper-arid, including during catastrophic events such as the hyperexplosion of the Toba volcanoes,” Ludovic Slimak, a researcher at the French National Center for Scientific Research and the University of Toulouse, said in an email. Slimak was not involved in the research.
The authors of the study were also able to examine the geology of the ancient river bed, which suggested that it ran slower and lower at that point than it does now.
“We can do that just by looking at the cobbles,” Kappelman said. “A very energetic river can move more boulders and cobbles than a less energetic (energetic) river. What cobbles we find for the ancestral river are smaller than the river today.”
Oldest known arrowheads?
The researchers also uncovered the remains of several small triangular points, which tantalizingly rank 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 prey. bigger.
Slimak, who studied similar points found in France dating back 50,000 years, agreed with the new study’s assessment of the artifacts.
“The authors also highlight very clear indicators that suggest archery was here 74,000 years ago,” Slimak said. “There is every reason, therefore, to consider … these ancient Homo sapiens as possessors of already highly developed technologies, largely freed from natural and climatic constraints, crucial factors for their later migrations, over all to understand every continent and every latitude.”
Ancient species of humans probably left Africa many times, but archaeologists and geneticists mostly agree that the most significant dispersal occurred with Homo sapiens, our own species – which left modern humans living in every corner of the world at last – about 70,000 to 50,000 years. since then.
The new research offers another possible scenario for how this dispersal happened and does not rule out previous theories, said Chris Stringer, professor and head of research on human evolution at the Natural History Museum in London. who called it an “interesting paper”.
“I’m sure each of these propositions will provoke debate among relevant specialists but I think the authors have made a plausible (but not conclusive) case for each of the scenarios they propose,” Stringer said via the email.
“Of course this new work doesn’t mean that humid corridors weren’t still important resources for dispersal out of Africa, but this work adds plausible additional possibilities during drier phases.”
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