The theory is simple and (nearly) apocalyptic: that a supervolcano at the site of current Lake Toba on the island of Sumatra exploded catastrophically some 75,000 years ago, causing global cooling and wiping out a significant number of the humans then colonizing across the globe.

A new study of the sediments of Lake Malawi in East Africa shows that there was no massive die-off of plants at low altitudes where humans lived in that period – thus showing that the “Toba Catastrophe Theory” must effectively be discarded, they report in the Journal of Human Evolution.

“It is surprising,” said Chad Yost, lead author, doctoral candidate at the University of Arizona. “You would have expected severe cooling based on the size of the Toba eruption – yet that’s not what we see… We determined that the Toba eruption had no significant negative impact in vegetation growing in East Africa.”

The two sediment cores were taken from the north end of the lake, closer to mountain, and from the central part of the lake. The layers they studied extended from 100 years before the eruption to 200 years after the event. (Prior researchers had isolated the layers of the sediments that contained the telltale glass and crystals from the Toba eruption, roughly 4500 miles to the east).

The scientists were especially looking for charcoal and phytoliths, the long-lasting parts of plants that contain silica. The theory is that the mass die-off of vegetation would cause wildfires, and thus, more charcoal from the burns. The phytoliths would have been the other remnants from the mass destruction.

The samples represented every 8.5 years within the 300-year range, they report. These layers were between 3 and 4 mm each, they report.

The scientists found some die-off of the plants on the mountainous side of the lake in the time immediately after the eruption. But they did not find any major fluctuations in the layers on the side of the lower elevations.

Since the theory of mass catastrophe included the timetable of a “bottleneck” in the human population worldwide, especially in this birthplace of humankind, the East African Rift system. They also point to recent genetic studies that show no genetic bottleneck at the time of the eruption.

“That a singular event in Earth history 75,000 years ago caused human population in the cradle of humankind to drop is not a tenable idea,” said Andrew Cohen, co-author, distinguished professor of geosciences at the University of Arizona.

“We hope this will put the final nail in the coffin of the Toba catastrophe hypothesis,” added Yost.