The Toba catastrophe theory holds that 70,000 to 75,000 years ago, a supervolcanic event at Lake Toba, on Sumatra (Indonesia), possibly the largest explosive volcanic eruption within the last twenty-five million years, plunged the Earth, which was already in an ice-age, into an even colder spell. This resulted in the world's human population being reduced to 10,000 or even a mere 1,000 breeding pairs, creating a bottleneck in human evolution. The theory was proposed in 1998 by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign.