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HomeScienceIndians likely survived super-destructive Toba volcano 74,000 years ago: Study

Indians likely survived super-destructive Toba volcano 74,000 years ago: Study

Archaeological evidence found at Dhaba in MP debunks the long-held theory that Indonesia's Mount Toba eruption led to the death of majority human population.

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Bengaluru: New archaeological evidence found at Dhaba, on the banks of the Middle Son River in Madhya Pradesh, reveals that a significant population in South Asia survived the destructive explosion of Indonesia’s Toba volcano 74,000 years ago.

The research, published in the journal Nature Communications, debunks the long-held theory that the Mount Toba volcanic eruption led to the death of the majority human population.

The study was conducted by researchers from Australia, USA, UK, and the University of Allahabad, University of Madras and Banaras Hindu University in India.

Stone tools found at the Dhaba site indicate humans have occupied the site continuously for the last 80,000 years — much earlier than believed. The tools found here are also similar to those in Middle Stone Age sites in Africa and Arabia, implying that they were all built by migrating Homo sapiens.


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The earlier theory

The Mount Toba explosion, is believed to be the most powerful volcanic eruption in the past 2 million years. It expelled 1,000 times more material than the eruption of Mount St. Helens in Italy in 1981 and 60 times more material than Indonesia’s Krakatoa explosion in 1883. It was 100 times stronger than the 1815 eruption of Mount Tambora in Indonesia, which caused the 1816 ‘Year Without a Summer’ in the entire northern hemisphere.

After the Toba explosion, just a few thousand members of the human population in Africa were believed to have survived. Those who survived were also believed to have been stuck in an evolutionary genetic bottleneck, which drastically decreased genetic variation and diversity. They had to adapt to harsher conditions and thus changed the path of human evolution.

However, this new study contradicts the theory and notes that the Toba super-eruption had minimal impact on the human population and did not actually cause the bottleneck. This adds to the already existing body of research, which used archaeological evidence to determine that the human population in Africa had survived the eruption. Genetic studies, too, don’t seem to indicate the population bottleneck.

The Dhaba excavation site | Credits:
The Dhaba excavation site | Credits: Clarkson et al., Nature Communications, 2019

Another long-held assumption was that after the eruption, the volcanic fallout from plumes, which reached heights of 30 kilometres, triggered a six to ten-year long ‘volcanic winter’ that blocked out the sun and rained down white ash all over India, Asia and many parts of Africa. This was believed to have been followed by a 1000-year long mini ice-age.

However, vegetation records from the Lake Malawi region of East Africa show no evidence of the supposed volcanic winter at all.


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More clarity regarding human migration

The Dhaba research adds more evidence to earlier studies undertaken regarding the destructive nature of the Toba volcano. Studies, within India, have found similar tools, sandwiching a layer of volcanic ash from Toba, indicating that tooling carried on after the eruption.The eruption had deposited an ash layer 15 cm thick over the whole of South Asia.

Even in Sumatra itself, analysis of fossilised teeth have shown that humans lived there as close to a year after the eruption.

Despite this evidence, the bottleneck theory continued to persist and the Dhaba site acts as a link between Africa and Australia, bridging a crucial geographical gap in our understanding of the history of human migration.

The tools found at the site show that the ‘Levallois technique’ — an early method of chipping stone into weapons — was used. The tools were buried in sediment dating 80,000 to 65,000 years ago and tools in younger sediment layers were shaped with more advanced techniques.

The definitive drop in human genetic diversity 70,000 years ago is now better explained by the founder effect — a limited number of people from a similar gene pool founding a new settlement — rather than the super-eruption. As humans migrated out, the genetic variation decreased. The new findings show that humans migrated out of Africa much earlier and expanded across Eurasia.

“Modern human dispersal out of Africa, and more importantly east of Arabia, must therefore have taken place before [65,000 years ago],” the authors write.

“The Dhaba locality serves as an important bridge linking regions with similar archaeology to the east and west,” they add.

“Our new findings contribute to a revised understanding of the global impact of the Toba super-eruption. While the Toba super-eruption was certainly a colossal event, global cooling may have been less significant than previously thought,” wrote two of the paper’s authors — University of Queensland’s Chris Clarkson and Max Planck Institute for the Science of Human History’s Michael Petraglia — in an article published in The Conversation.


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