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 was much harder. There are just 10 of them in each gram of sediment, and each one is just 0.04 millimeters wide. To recover them, Gene Smith, from the University of Nevada at Las Vegas, designed new techniques that use special liquids to separate particles of a specific size. The shards come out with other gunk, and specialists pick them out under a microscope. “Then you can do a chemical analysis on them, which is a whole new struggle because you’re trying to target something that’s 40 microns wide with a beam that then destroys it,” says Marean. “It’s crazy. It took us years. I first proposed this study in 2005.”
They found that the shards are almost chemically identical to others that have been found in India, Malawi, and Toba itself, all of which have been traced to the super-eruption. They were also found in sediments that were roughly the right age—around 74,000 years old. They must have come from Toba.
The team tracked down even more shards at a half-moon bay that’s just a few miles away, and that’s also replete with human-made artifacts. Usually, it would be impossible to say whether people who lived in two separate archaeological sites actually lived at the same time, because the dating methods that archaeologists use come with large error ranges. But the cryptotephra solve that problem because they were deposited in a two-week period. They unequivocally show that the people from the headland and the bay must have belonged to the same social group. They probably knew each other. They may even have been the same people, foraging in the bay by day and sleeping in the headland at night.
“This is a Holy Grail moment in geochronology,” says Marean. “It’s so, so rare for us to be able to speak about things at that temporal resolution.”