Sometimes various scientific disciplines come together in an almost musical way to produce new knowledge that gives us yet another thing to be terrified of.
That's what happened when volcanologists and geneticists looking at very different sets of data both inferred that something really big happened approximately 75,000 years ago.
For Dr. Michael Rampino and other earth scientists, it was ocean cores that pointed to a sudden 10-degree drop in ocean temperatures 75,000 years ago. As he told PBS' NOVA, "At the time I thought, 'There's something wrong here, this isn't normal. This isn't the way climate usually works.' It usually works on a much slower, more steady basis."
For population geneticists, it was DNA evidence of a population bottleneck about the same time. The evidence seemed to be pointing towards a catastrophic event that greatly reduced human population around the world: perhaps as much as 97-99 percent.
What is a "Toba"? Toba is (not was, is) a supervolcano on the island of Sumatra. All volcanoes are rated on something called the Volcanic Explosivity Index, or VEI. For our purposes, all you need to know is that the index runs from 0 to 8; Mt. St. Helens, which ejected approximately one cubic kilometer of material, rates a five; and the index is logarithmic, i.e., each whole number represents a 10-fold increase in material ejected. Thus, Mt. Pinatubo, a VEI 6, ejected 10 times more material than Mt. St. Helens. A VEI 7 would eject 100 times more and a VEI 8, a.k.a. a supervolcano, 1000 times more.