Around 74,000 years ago, the Toba supervolcano erupted on the Indonesian island of Sumatra. It was the biggest volcanic eruption of the last 2 million years, unleashing 2,800 cubic kilometers of magma. That’s enough to bury the entire United States in a foot-thick layer of ash and rock.
In the 1990s, several scientists argued that Toba’s unprecedented outburst radically changed the world’s climate, blocking out sunlight and lowering global temperatures by several degrees for many decades. This “volcanic winter,” it is said, almost drove humans to extinction, leaving behind a measly group of a few thousand survivors, from whom we today are descended. The “Toba catastrophe theory” is highly controversial, and other researchers have argued that it greatly overestimates both the degree of climate change that the volcano inflicted, and its effect on our ancestors.
Now, into the fray comes a new study from an unlikely location. In a cliff near Mossel Bay, a town on South Africa’s south coast, scientists have discovered a layer of microscopic glass shards. Known as cryptotephra, these shards are the products of Toba’s wrath, created when the volcano superheated the silica within its expunged rock. They drifted in the air over 5,500 miles and fell on southern Africa as the sparsest of drizzles. And they settled among bones, tools, and other signs of human occupation.
The fact that these artifacts exist in plentiful numbers both above and below the shards suggests that the humans who once lived in South Africa weren’t affected by Toba’s wrath as one might expect if the supervolcano had truly brought on a global decades-long winter. If anything, they thrived. “We showed that after the input of the shards, human occupation at the site actually increased dramatically,” says Curtis Marean, from Arizona State University. “We never expected that.”
“This is the first time we can say: Here is what humans were doing before and after [the eruption],” adds Christine Lane, a researcher from the University of Cambridge who helped to study the cryptotephra. “And I think we were doing really well.”
“If Toba had triggered a major global climate event, Africa probably would have been affected, and they see no evidence of that,” says Britta Jensen, a tephra expert from the University of Alberta who wasn’t involved in the new study.
Marean’s team has spent years working at Pinnacle Point—a rocky headland from which they’ve uncovered 400,000 artifacts. Finding the cryptotephra …read more
Source:: The Atlantic – Science