Human Evolution Has Not Been Affected By The Most Powerful Super-volcano Eruption In The Last 28 Million Years

Mount Toba, located on the current island of Sumatra, erupted 74,000 years ago and was Earth's greatest eruption in the previous 28 million years. Consider that, despite the fact that the eruption occurred in Indonesia, an ash layer of 6 inches deep was deposited across the whole Indian subcontinent. A total of 1,700 cubic miles of rock erupted, equivalent to over 3 million Empire State Buildings, forming a crater lake visible from space.

Toba was at least two orders of magnitude greater (and ten times more powerful) than Tambora, the greatest eruption known to modern humans. Years of unusually unstable weather in Europe, Asia, and America followed the eruption of Tambora in 1815 when volcanic ash and gases altered the Earth's climate. Even more, ash was ejected into the atmosphere by Toba.

In 1998, anthropologist Stanley Ambrose discovered the link between modern humans' diminished genetic variability and the Toba eruption. According to genetic data, the human population abruptly fell around 74,000 years ago. The specific reason for this genetic bottleneck is uncertain, however, the diminished genetic variability could be explained by a volcanic winter following the Toba eruption. The climate and environment abruptly shifted, killing most early people in Europe and Asia, and only a tiny group with little genetic variability survived by chance in Africa. Based on mitochondrial DNA, there is some evidence that the human race was reduced to only a few thousand individuals. We, as modern people, are descended from a small group of survivors.

Recent finds, on the other hand, suggest differently. The 65,000-year-old stone tools discovered in northern Australia caused quite a stir. Humans must have migrated from Africa to Asia much earlier than originally assumed, between 75,000 and 60,000 years ago. Two human teeth discovered in the Lida Ajer archaeological site in Sumatra suggest that people lived on the island at the time of Toba's eruption. The researchers were able to date the human bones to 63,000-73,000 years ago, right in time for the Toba eruption, using contemporary dating techniques.

Stone tools created by early men and recovered in sedimentary levels beneath and above the ash layer of Toba reveal no major variations, according to archaeological digs in India. Furthermore, stone tools discovered near the Son River in central India resemble stone tools found in the Near East and Australia. The notion that the Toba eruption triggered the demise of early societies does not suit this cultural continuity across time and across such a large territory. The remains of animals found in the archaeological excavation were examined by zoologists, who found no evidence of faunal alterations. Despite significant ashfall (up to 20 feet in some regions), the Toba eruption had no long-term environmental consequences.

An alternate idea to explain the apparent genetic bottleneck is now popular among anthropologists. Favourable conditions in Africa led to population expansion around 65,000 years ago, and smaller groups of modern humans fled Africa between 65,000 and 75,000 years ago. They came across ancient hominids such as Neanderthals and Denisovans in Europe and Asia. Because of the competition for limited resources, the number of newcomers has remained low. Without evoking any volcanic catastrophe, the low genetic diversity might be explained by the very small number of modern people who survived those migration waves.

Volcanologists also suggested a theory for why the Toba eruption had such little impact on the climate and ecosystem. Sulfur compounds originate in the upper layers of the Earth's atmosphere as a result of sulfur-rich lava. Sulfur compounds combine with water vapour to generate aerosol droplets, effectively obscuring the Earth's surface from sunlight and resulting in global cooling. Unlike Tambora, the Toba eruption likely spewed significantly less sulphur than originally thought.


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