Quick recovery
If the area had seen dramatic cooling because of all the ash spewed into the atmosphere, living matter near the lake surface would likely have died off, significantly altering the composition of the lake's mud. However, when the researchers investigated algae and other organic matter from the layer that contained the ash from Toba, they saw no evidence of a significant temperature drop in East Africa. Apparently, "the environment very quickly recovered from any atmospheric disturbance that may have occurred," Lane said.
But these results, detailed online April 29 in the journal Proceedings of the National Academy of Sciences, don't mean that super-eruptions aren't as big a risk to Earth's denizens as previously suggested.
"It is important to realize that every volcanic eruption is different and the Youngest Toba Tuff provides only one example," Lane said. "The impact of an eruption depends not just on the amount of ash erupted, but also the composition and volume of aerosols, how high in the atmosphere the ash is injected and the meteorological conditions at the time."
As for what might explain the near-extinction humanity apparently once experienced, perhaps another kind of catastrophe, such as disease, hit the species. It may also be possible that such a disaster never happened in the first place — genetic research suggests modern humans descend from a single population of a few thousand survivors of a calamity, but another possible explanation is that modern humans descend from a few groups that left Africa at different times.
Future research will analyze what effects Toba may or may not have had on other lakes in East Africa.
"Whilst from this we can hypothesize that the global climatic impact was not as dramatic as some have suggested, we will need to find similarly high-resolution records of past climate from other regions that also contain Youngest Toba Tuff in order to definitively test this," Lane said.