Tanzania: Mount Toba, the Biggest Volcanic Eruption in the Last 2.6 Million Years, May Not Have Nearly Wiped Out Humanity As Some Have

6 million years, may not have nearly wiped out humanity as some have suggested. Around 74,000 years ago, a caldera on what is now Sumatra emptied thousands of cubic kilometers of magma in about two weeks—roughly a thousand times more than Mount Pinatubo spewed in 1991. "People thought it might have caused massive cooling of the planet, and hence threatened the survival of our ancestors, said Jinheum Park, a geoscientist at Johannes Gutenberg University in Mainz, Germany. Park and his colleagues searched for records of that catastrophe in mud from the bottom of a small crater lake on the Kenya-Tanzania border.

Instead, they found the eruption's effects lasted under two years and amounted to perhaps half a degree of cooling. Volcanic eruptions inject sulfur dioxide into the stratosphere, where it becomes a haze of tiny droplets that reflect sunlight back into space. Bigger eruptions eject more sulfur dioxide and, in principle, cause more cooling—but this trend stops working when the eruption exceeds a certain magnitude. "Bigger sulfate aerosols settle quickly, because they are heavier, Park explained, making them less effective at scattering incoming solar radiation.