A forest fire has led to a chance discovery of debris from the impact of a meteorite 1.85 billion years ago, more than 450 miles away at Sudbury, Ontario.
Geologists had scheduled a field trip in May along the Gunflint Trail in northeastern Minnesota, but most areas they wanted to explore were closed because of a wildfire that charred more than 118 square miles.
Geologist Mark Jirsa of the Minnesota Geological Survey went up the trail to scout new locations and, in a spot he had never visited before, stumbled across debris now linked to the Sudbury impact.
That impact created a crater more than 150 miles across, scattering rock and dust over nearly a million square miles.
"It's fairly dark rock," Jirsa said. "They look like concrete, but in this concrete you would throw pieces of rock of all sizes and shapes and in all possible orientations."
Previously, material thrown out by the impact had been found as far from Sudbury as Hibbing, about 125 miles farther to the southwest from Grand Marais.
However, the tiny fragments at Hibbing were found in core samples from 800 to 1,000 feet below the surface, while the rock layer containing larger chunks at the Gunflint site lies exposed.
"I think the excitement for the people of Minnesota is that we are one place in the world where you can see evidence of an ancient meteorite impact," said University of Minnesota geology professor emeritus Paul Weiblen, who is studying the debris.
"This is the second-oldest and second-largest impact crater in the world."