About 74,000 years ago, a volcanic eruption more powerful than any in Earth’s modern history triggered global consequences that lasted hundreds of years. Geologists hypothesize that the Toba caldera, a supervolcano in present-day Sumatra, blanketed South Asia with ash, blocking the sun and causing a decade-long volcanic winter that hampered the growth of vegetation. During this time, the humans who relied on wild plants and animals for survival faced a serious threat to their existence. But, as scientists report in the journal Nature on Monday, a hardy group of people made it through — possibly even with enough to share with others.

Not all scientists agree with this hypothesis, but new research lends it significant support, showing that the effects of Toba’s eruption were incredibly widespread, spanning the Indian Ocean. In a research letter, geologists show evidence that shards ejected from Toba reached all the way to modern-day South Africa — a distance of over 5,500 miles. In the years that followed the eruption, human activity appears to have increased at the extreme southern tip of Africa. Researchers say this shows certain human populations thrived in the aftermath of a natural disaster that likely caused serious problems for other groups.

Scientists say they found tephra — rock fragments ejected by the eruption of Toba — all the way across the Indian Ocean.
Scientists say they found tephra — rock fragments ejected by the eruption of Toba — all the way across the Indian Ocean.

The key to this research is tephra, the rock shards that a volcano ejects. In this case, researchers found glass tephra in two dig sites on the south coast of South Africa at the same depth as remnants of human activity. By comparing these shards to samples from around Toba, geologists grew fairly certain that the tephra in Africa came from Toba.

“Glass shards are a form of tephra that preserve a record of the chemical composition of the lava erupted during the eruption. The shapes and sizes of the shards also provide information about the nature of the eruption,” Gene Smith, Ph.D., professor emeritus of geology at the University of Nevada, Las Vegas, and the first author on the study, tells Inverse.

“We can tell quite a bit about a volcanic eruption by studying products ejected from the volcano.”

Smith supervised the chemical analysis of tephra samples removed from the dig sites, which he and his colleagues used to show that they did indeed originate in Sumatra, from the ancient eruption of the Toba caldera. Even though the effects of this cataclysmic eruption reached Africa, the people who lived at the particular sites that the researchers examined were able to live through it all.

The authors suggest the coastal resources used by the people who lived there were less affected by resources further inland. And they didn’t just survive: Archaeologists on the team found that human activity actually increased there, perhaps because groups of people moved from inland areas whose plant or animal life had been affected by the volcanic winter.

Students excavating one of the dig sites in South Africa.
Students excavating one of the dig sites in South Africa.

“It is possible that people moved out of terrestrial locations and into this more productive coastal zone,” Curtis Marean, Ph.D., professor of archaeology at Arizona State University and one of the study’s authors, tells Inverse. “Think of it as a refuge.”

Smith says that even though ancient humans survived the eruption of Toba and its after-effects, this historical example of an extreme volcanic eruption might not have much in common with what we could expect from the modern world if such a thing happened in our lifetime.

“Hunter-gatherer economies are very resilient, but I don’t think the complex modern economies are,” he says. “A Toba-like event is a civilization killer for us. Perhaps our study will waken people up to the potential of volcanic catastrophe.”

Abstract: Approximately 74 thousand years ago (ka), the Toba caldera erupted in Sumatra. Since the magnitude of this eruption was first established, its effects on climate, environment and humans have been debated1. Here we describe the discovery of microscopic glass shards characteristic of the Youngest Toba Tuff — ashfall from the Toba eruption — in two archaeological sites on the south coast of South Africa, a region in which there is evidence for early human behavioural complexity. An independently derived dating model supports a date of approximately 74 ka for the sediments containing the Youngest Toba Tuff glass shards. By defining the input of shards at both sites, which are located nine kilometres apart, we are able to establish a close temporal correlation between them. Our high-resolution excavation and sampling technique enable exact comparisons between the input of Youngest Toba Tuff glass shards and the evidence for human occupation. Humans in this region thrived through the Toba event and the ensuing full glacial conditions, perhaps as a combined result of the uniquely rich resource base of the region and fully evolved modern human adaptation.

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