UMD scientists douse volcano extinction theory

A study led by University of Minnesota Duluth scientists "puts the nail in the coffin" on a theory that one of Earth's largest volcanic events decimated animal and plant life 75,000 years ago.

Ben Chorn
Ben Chorn received his master's degree from the University of Minnesota Duluth last May. (Photo courtesy of Ben Chorn)

A study led by University of Minnesota Duluth scientists "puts the nail in the coffin" on a theory that one of Earth's largest volcanic events decimated animal and plant life 75,000 years ago.

Tom Johnson of the Large Lakes Observatory said a new study by former UMD graduate student Ben Chorn published last week in the Proceedings of the Natural Academy of Sciences shows that the "super-volcano" Toba in Indonesia did not have the impact many have theorized over the years.

"This is concrete," Johnson said. The finding also helps other scientists looking to date materials beyond the reach of carbon dating, which can mark ages only 40,000 to 50,000 years.

"It's kind of a golden spike in the whole age model," Johnson said.

Chorn said the fact that a grad student made the historic find makes the story "kind of surreal."


The Toba layer find is a first for Africa. The cores sampled came from 4,300 miles west of the volcano, on the bed of Lake Malawi, a long lake that touches Tanzania, Malawi and Mozambique.

What the samples revealed are layers above the Toba volcano era that show there wasn't the type of "volcano winter" that would have cut human population into the mere thousands.

"The climate didn't change much at all," Johnson said.

Search for an event

The find is important because it narrows the bed of theories scientists have about a calamitous, near-extinction event that would explain genetic research linking modern humans to a small population of a few thousand survivors.

Oxford University's School of Archaeology in England helped confirm what Johnson and his team found. Geologist Christine Lane talked about the collaboration with Chorn in an online story with Our Amazing Planet.

"We first started looking for the Toba ash a few years back, but it's a bit like looking for a needle in a haystack, so it took a while," Lane said. "Between myself and my co-author Ben Chorn, we systematically processed every centimeter of sediment between 24 to 46 meters (78 to 150 feet) depth in the central basin core. The layer is so small that if we leave any gaps in our search, we could miss it completely."

Johnson said he conceived the lake bed drilling project, which began in 2005. The sections are stored at the University of Minnesota's Minneapolis campus and have been studied ever since.


Chorn, from New Brighton, just north of Minneapolis, said that when he was accepted to grad school, he had to pick a project. His lifelong love of lakes and fascination with volcanoes sold him on Johnson's work.

"That seemed the most interesting," Chorn said.

Getting to work

Johnson and others had established good climatology information from the samples. It was Chorn's job to get better age records, work he'd done before as an undergraduate at Rocky Mountain College in Billings, Mont. He also was looking for layers that showed African volcanic activity and the slight chance of finding signs of the Toba event.

He found some ash layers that looked different and was sent to Oxford to learn how to find the microscopic differences. It was a two-week "crash course" in detecting microscopic traces of volcanic activity.

"We knew that if we were to find it, that would be pretty big," Chorn said from Billings on Tuesday, where he's been working in oil exploration since August.

He found the Toba layer, and then the scientists at Oxford confirmed it. That was December 2011.

"It was pretty amazing," Chorn said. "We just made a big discovery."


"This has got to be it," Johnson recalls saying of the "a-ha moment."


Chorn began work on his paper and made presentations, including his thesis defense to culminate his graduate work.

"It puts quite a feather in his cap," Johnson said of Chorn.

The Large Lakes Observatory is global in its scope, Johnson said. And what it learns is useful for study of Lake Superior, he said.

"We have a reputation for working on the large lakes of the world," Johnson said.

He said the physiology they've found on those lakes can be compared to work done on Lake Superior.

The Toba finding will only enhance the reputation of UMD's observatory, Johnson said.

"This is a big discovery," Johnson said.

Chorn said he had trouble finding a job after leaving UMD. That may not be the case anymore.

"This is something to put on my resume," Chorn said.

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