About 74,000 years ago, Mount Toba, on the island of Sumatra (now Indonesia), experienced a massive eruption, one of the largest in Earth's history, which may have caused major disruption to 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, due to genetic evidence suggesting a sharp decline in the human population. But now, a study of an archaeological site in northwestern Ethiopia occupied by early modern humans has added to a growing body of evidence that suggests the event may not have been so horrific.
Instead, the new research reveals that humans at this site, known as Shinfa-Metema 1, adapted to the arid conditions caused by the volcanic eruption in a way that may have facilitated humanity's 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 humans occupied the site before and after the volcanic glass eruption more than… 4 thousand kilometers away.
“These fragments are less than the diameter of a human hair,” said John Kappelman, a professor of anthropology and geological sciences at the University of Texas at Austin. “Although they are very small, they are large enough to analyze chemistry and trace elements.” He is lead author of the study, published March 20 in the journal Nature.
By collecting evidence from fossils and artifacts found at the site, along with geological and molecular analyses, the team began to understand how the humans who lived there survived despite the potential climate change brought about by the volcanic disaster.
Excavations at the Shinfa-Metema 1 site revealed that a group of humans survived the massive eruption of Mount Toba 74,000 years ago. John Kappelman and Marsha Miller
Catch a fish
To understand the climate at the time of the eruption, Kappelman and his colleagues analyzed oxygen and carbon isotopes, which are variations of the same element, from ostrich eggshells and fossilized mammal teeth. This work explored water consumption and revealed that the animals ate plants that were more likely to grow in drier conditions.
“Isotopes are incorporated into hard tissues. That's why, in the case of mammals, we look at teeth, at tooth enamel, but we also find them in the ostrich egg shell,” he said.
Analysis of the flora and fauna of the site also found an abundance of fish remains after the eruption. The study indicated that this discovery may not be surprising given the site's proximity to the river, but fish are rare in other Stone Age sites from the same period.
“People started increasing the proportion of fish in their diet when Toba arrived,” he said. “They were catching and processing about four times more fish (than before the eruption).”
“We think this is because if Toba is in fact causing more drought, it means the rainy season will be shorter, which means a longer dry season.”
The team hypothesized that a drier climate unexpectedly explained the increased reliance on fish: as the river shrank, fish became trapped in shallow ponds or streams, where humans could catch them more easily.
Blue Corridor Vs. Green corridor
The fish-rich pools of water likely created what the team described as a “blue corridor” along which early humans moved north out of Africa once the fish were depleted. This theory contradicts most other models that suggest that the main human migration out of Africa occurred through “green corridors” during wet periods.
“This study (…) demonstrates the great resilience of Homo sapiens populations and their ability to easily adapt to any type of environment, whether very wet or very dry, including during catastrophic events such as the severe explosion of the Toba River,” said Ludovic Slimak, a 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's authors were also able to explore the geology of the ancient riverbed, suggesting that at that time it flowed slower and lower than it does now.
“We can do this just by looking at the rocks,” Kappelman said. “A very active river can move larger rocks and stones than a river that is not 'lively'. The (stones) we found in the ancestral river are smaller than they are in the river today.”
The excavation team was able to build a detailed picture of what happened at the site in Ethiopia about 74 thousand years ago. Lawrence C. Todd
Oldest known arrowheads?
Researchers also discovered the remains of several small triangular points, which are some of the earliest examples of bow and arrow use and provide evidence that locals may have used bows and arrows to hunt fish and other larger prey.
Slimak, who studied similar nails discovered 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 archery was present here 74,000 years ago,” Slimak said. “Therefore, there is every reason (…) to consider these ancient Homo sapiens as carriers of very advanced technologies indeed, largely free from natural and climatic constraints, which are crucial factors for understanding their subsequent migrations, across all continents and under all latitudes.”
Ancient human species likely left Africa several times, but archaeologists and geneticists largely agree that the most significant spread of Homo sapiens, our own species — which eventually led to modern humans living around the world — occurred around 70,000 to 50,000 years ago. person. Years ago.
Chris Stringer, professor and research leader in human evolution at the Natural History Museum in London, said the new research presents another possible scenario for how this dispersal occurred, without ruling out previous theories, which he described as an “interesting paper.”
“I'm sure each of these suggestions will generate controversy among the experts involved, but I think the authors make a plausible (though not definitive) case for each scenario they propose,” Stringer said in an email.
“Of course, this new work does not mean that wet corridors will not remain important dispersal channels out of Africa, but this work adds additional reliable capabilities during drier phases.”