Landsat image of Lake Toba
An eruption of a super volcano 74,000 years ago was not enough to stop humanity, as artifacts at a paleolithic site in central India suggest. The study is the latest strike against a hotly debated proposal that suggests that the Indonesian super volcano Toba eruption has had a major impact on human evolution. The idea is that the outbreak caused a global cooling that killed most of the people who had spread from Africa to Europe and Asia. At the Dhaba site in Madhya Pradesh, India, archaeologists found stone tools in sediment layers that spanned thousands of years before and after the eruption – evidence that human life continued.
An old apocalypse?
Today, the super volcano Toba lies under the picturesque Lake Toba on the Indonesian island of Sumatra. Seventy-four thousand years ago, it broke out in the middle of an important chapter in the takeover of the world by humanity. One of the biggest questions in archeology in recent years has been when and how people first spread beyond Africa to different regions of the world. The answers lie in petrified skeletons, objects left behind and the DNA of modern humans.
Fossil evidence suggests that humans reached the Levant about 200,000 years ago, the Arabian Peninsula about 85,000 years ago, and northern Australia about 65,000 years ago. But the genomes of modern humans suggest that the ancestors of modern African and non-African peoples separated from a common ancestor about 70,000 years ago. At first glance, these lines of evidence don't seem to match, and some paleoanthropologists say it is because a sudden, long period of global cooling has changed the environment around the world in a very drastic way. The resulting crisis reportedly killed most of the people living at the time, leaving only a few thousand survivors.
According to the hypothesis, the smoking weapon is the super volcano Toba. When Toba erupted 74,000 years ago, it spread a thick layer of ash to Tanzania, 7,400 km to the west. Volcanologists use a scale called the volcanic explosiveness index to measure the explosive power of an eruption. The eruption of Vesuvius in 79 AD scored a 5 on this scale, while Toba scored an 8 (out of a possible score of … 8) at the level of the Yellowstone Supervolcano eruption 630,000 years ago. Toba's eruption would have released billions of tons of sulfur dioxide and other chemicals into the atmosphere and triggered several years of relentless volcanic winters – and that's a best case scenario.
But geologists, paleontologists, and paleoanthropologists are still discussing what impact Toba had on the Earth's climate, how long it lasted, and what happened to people and other species. Greenland ice cores indicate that the earth's climate suddenly became colder at the time of the eruption and remained cold for about 1,000 years, but the scientists do not agree on whether to blame Toba or other climate processes. Some models point to at least a few decades of colder climate after the eruption, while others only point to a few years. Not surprisingly, scientists in various areas are still discussing how this would have affected life. The same fossil species occur above and below the Toba ash layer in lake sediments of Lake Malawi in East Africa, suggesting that the conditions have not changed enough to disrupt life.
And the archaeological evidence from Dhaba suggests that the people of India did not die in droves either. In fact, the sediment layers directly above the Toba ash layer contain as many artifacts as the one directly below.
Sedimentary layers in Dhaba span 80,000 years of human occupation.
Adapt and survive
In Dhaba, near the banks of the Son River in central India, you can follow the evolution of stone tooling technology by looking at the artifacts buried layer by layer in an accumulated sediment of 80,000 years ago. These layers are key to answering an important question about Toba's role in human history: Did people come to India before the outbreak with the same stone tooling technology they brought back from Africa, or did they come with newer toolkits tens of thousands of years later ?
According to luminescence dating from nearby sediments, the oldest stone tools in Dhaba are between 75,000 and 82,000 years old and date the Toba eruption several millennia before. And on the other side of the tuff layer deposited by Toba (whose argon isotope dating is 74,000 to 76,000 years old), the same stone tools keep popping up without being interrupted by anything that looks like a sudden apocalyptic depopulation. They still exist 34,000 years before they gradually give way to another stone tool technology, which is much smaller, a few centimeters long "microblades". Overall, Dhaba seems to indicate that before the Toba outbreak, people arrived in central India, survived the aftermath and stayed here – which is not too good for the idea of a population bottleneck.
The tools that were manufactured and used in Dhaba in the millennia before the Toba eruption are strikingly similar to the tools found at locations in Africa about 280,000 years ago, in Arabia 100,000 to 74,000 years ago, and in Northern Australia about 65,000 years ago (This timeline should look fairly familiar. They are sharp flakes, blades, and scrapers made by chopping off pieces of prepared stone cores – a technology that archaeologists call Levallois. India is firmly anchored in the timeline of human migration and "one." important bridge that connects regions with similar archeology in the east and west ”.
Of course, it is likely that conditions in Dhaba have changed at least a few years after the outbreak – a 2009 study of old pollen grains suggests that there was some deforestation in South Asia at that time. Adapting to changing climates and new landscapes has always been a human strength, and this is shown by the archaeological record in Dhaba: not that nothing has changed, but that people have probably adapted, coped with and continued.
Nature Communications, 2020 DOI: 10.1038 / s41467-020-14668-4 (About DOIs).