One of the largest eruptions in Earth’s history could have wiped out humans. Here’s how scientists say some survived

By Katie Hunt, CNN

(CNN) — About 74,000 years ago, Sumatra’s Mount Toba experienced a super-eruption, one of the largest in Earth’s history, potentially kicking off a massive disruption in the world’s climate.

Some scientists have suspected a volcanic winter resulting from the eruption was a big enough shift to wipe out most early humans due to genetic evidence suggesting a steep drop in the human population. But now a cutting-edge study on an archaeological site in northwest Ethiopia once occupied by early modern humans has added to a growing body of evidence that suggests the event might not have been so apocalyptic.

Instead, the new research found humans in that location, known as Shinfa-Metema 1, adapted to the arid conditions brought on by the volcanic eruption in a way that may have facilitated humanity’s pivotal 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 sediment at the Shinfa-Metema 1 site, near Ethiopia’s Shinfa River, show humans were occupying the site before and after the volcano erupted more than 4,000 miles away.

“These fragments are less than the diameter of a human hair. Even as tiny as (that) they are still big enough to analyze the chemistry and the trace elements,” said John Kappelman, a professor of anthropology and geological science at the University of Texas at Austin and lead author of the study, which published Wednesday in the journal Nature.

By piecing together clues from the fossils and artifacts found at the site, along with geological and molecular analysis, the team began to understand how the humans living there forged ahead despite the likely climate shift that the volcanic cataclysm triggered.

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 the animals ate plants that were more likely to grow in drier conditions.

“The isotopes are incorporated in the hard tissues. So for 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 found an abundance of fish remains in the aftermath of the eruption. The finding is perhaps not surprising given how near the site was to the river, but fish are rare in other Stone Age sites from the same period, the study noted.

“People start to increase the percentage of fish in the diet when Toba comes in. They’re capturing and processing almost four times as much fish (as before the eruption),” he said.

“We think the reason for that is because if Toba is in fact, creating more aridity, that means it’s going to be a shorter wet season, which means longer dry season.”

The team theorized that the drier climate, counterintuitively, explains the increased reliance on fish: As the river shrank, fish were trapped in water holes or shallower streams that hunters could more easily target.

Blue vs. green corridor

The fish-rich water holes may have potentially created what the team described as a “blue corridor,” along which early humans moved north out of Africa once they were depleted of fish. 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, a researcher at the French National Centre for Scientific Research and the University of Toulouse, in an email. Slimak was not involved in the research.

The study authors were also able to explore 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 by just looking at the cobbles,” Kappelman said. “A very energetic river can move bigger boulders and cobbles than a river that isn’t that (energetic.) What (cobbles) we find for the ancestor 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 the use of archery and provide clues that the site’s inhabitants might 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 suggesting the existence of archery here 74,000 years ago,” Slimak said. “There is therefore every reason to … consider these ancient Homo sapiens as bearers of already highly advanced technologies, largely emancipated from natural and climatic constraints, crucial factors for understanding their migrations later on, across all continents and under all latitudes.”

Ancient species of humans likely left Africa multiple times, but archaeologists and geneticists largely agree that the most significant dispersal of Homo sapiens, our own species — which ultimately led to modern humans living in every corner of the globe — took place around 70,000 to 50,000 years ago.

The new research offers another potential scenario for how this dispersal happened while not ruling out previous theories, said Chris Stringer, a professor and research leader in human evolution at the Natural History Museum in London, who called it an “intriguing paper.”

“I’m sure each of these propositions will fuel debate amongst 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 doesn’t mean that humid corridors were not still important conduits for dispersals out of Africa, but this work adds credible additional possibilities during more arid phases.”

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