Did a supervolcano nearly wipe out humanity?

The ash says otherwise, in Africa. The Toba layer turns up in Lake Malawi sediments more than 7,000 kilometers west of the volcano. It comes with no major change in sediment composition and no sign of a volcanic winter, which implies the eruption did not significantly affect East African climate.

The eruption of Mount Toba in Sumatra 75,000 years ago was the most explosive volcanic event of the Quaternary. It produced voluminous ash deposits across much of the Indian Ocean, the Indian Peninsula and the South China Sea.

A major climatic downturn in the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols from the Youngest Toba Tuff. Those events coincide roughly with a hypothesized human genetic bottleneck, and some have speculated that the climate shift nearly finished early modern humans.

The argument was unresolved because the evidence came from the wrong places. Others had argued that conditions would not have been severe enough, and that modern humans may already have expanded beyond Africa by then.

So the authors went looking for the ash in Africa, and found it as a cryptotephra layer in Lake Malawi sediments more than 7,000 kilometers west of the volcano. That layer is an isochron for the whole record. It arrives with no major change in sediment composition and no evidence for substantial temperature change, implying the eruption did not significantly impact East African climate and was not the cause of a bottleneck.