Scientists have discovered a vast, ancient meteorite crater in southern Alberta.

Doug Schmitt, a University of Alberta researcher, says some time between 50 million and 70 million years ago, a huge chunk of space debris at least the size of an apartment block crashed into marshy, subtropical plains near what is now the hamlet of Bow City, near Brooks, Alta.

Geologist Doug Schmitt says some time between 50 million and 70 million years ago, a huge chunk of space debris at least the size of an apartment block crashed into marshy, subtropical plains near what is now the hamlet of Bow City. (Hand out/Canadian Press)

It left a hole up to two and a half kilometres deep and eight kilometres wide. The blast would have been 200 times stronger than the most powerful nuclear device ever detonated, so intense that anything alive within 200 kilometres would have received first-degree burns.

But after eons of erosion, so little is left of the crater that it had to be discovered by accident, Schmitt said.

"It's buried," he said. "There isn't a lot to see."

Crater fully underground

A geologist was doing some routine mapping of underground layers a few metres beneath the surface when he noticed something unusual.

"He noted there was a circular kind of disturbance, but it was completely covered."

Schmitt said his lab was called in. Using seismic data from industry to create a complete image of the feature, they realized it was most likely to be an impact crater, complete with a central peak where the meteorite would have struck. The size of the object can only be estimated.

The meteorite crater was found near Bow City, a hamlet just west of Brooks, Alta. (Google Maps)

A meteorite composed mostly of iron would have had to have been between 300 metres and 500 metres in diameter to create that size of a crater. If the meteorite was rock, it would have had to have been a kilometre across.

Schmitt said the crater is a rare opportunity to study the floor of an impact crater.

"We're able to get at the lower parts of (a crater) and see how rocks have been moved around."

His team is now looking for certain types of minerals that form only under certain conditions so as to confirm the crater is from a meteor impact. But he doesn't have much doubt.

"We're pretty confident it can only be a meteorite impact. It's pretty clear."