Sunday, September 18, 2016

Is the world's biggest crater in Quebec?

You would think the largest crater on Earth would be an easy thing to spot.

But evidence of where a meteorite, or even a larger asteroid, would have struck the Earth can be so hard to find because it can actually be microscopic.

Still, a team of Quebec geologists believe they have pieced together traces of a 500-kilometer crater in the Chibougamau area, 500 kilometres north of Montreal.

"It will be the biggest crater found on Earth," said Francine Robert. The geologist, who works under Serge Genest at Groupe Omegalpha, said craters of this size can be seen on other planets, so it's reasonable to think an asteroid of this size could have also hit the Earth.

And, if so, the find would be more than an anomaly.

"It will be quite interesting for scientists because to know how these craters are really, because we can see them on the moon on Mars and on other planets, but nobody can put a foot on them and see what the rocks are really like," said Robert, who, along with Genest, has been working on this project with Normand Goulet, a professor of Earth and atmospheric science at the Université du Québec à Montréal (UQAM).

The Earth erases its craters

Unlike barren celestial bodies like the moon and Mars, the Earth's crust is constantly changing due to shifting plate tectonics and erosion, making a crater that might have formed millions of years ago hard to find.

Beyond that, Robert's crater would be 2.1 billion years old. She believes only a quarter of it is still exposed today.

Still, she says there were some features in northern Quebec that first attracted her team's attention. For one, the Misstassini and Albanel lakes have an unusual crescent shape.

"These lakes have never been explained for their shape, for the arc shape that they have," Robert said.

In 2003 and 2004, the team noticed something odd when visiting the formations around the town of Chibougamau.

The area is supposed to be the result of a glacial deposit, but Robert says they found fragile glass shards in the rock that would not have survived under a glacier.

About two or three years later, they found microscopic signs of impact in the Otish basin, near the Otish mountains, about 300 kilometers north-east of Chibougamau.

Now, the team believes they have found shatter cones near Lake Albanel, rock formations which can only be created by the heavy impact of a meteorite, or a nuclear explosion.

Casting doubt

Some scientists see holes in the crater theory.

Gordon Osinski, who studies impact craters, says that while he hasn't been to the site in person, the team's photos do not show the telltale signs of a meteorite.

"We're really not looking at shatter cones," says the planetary geology professor at Western University's department of Earth sciences.

"There are certain key things and attributes and properties of shatter cones that these features just do not show."

He said shatter cones should have lines on the rock that point to an apex.

Robert, herself, says it will probably take her team another two to three years of research to establish the theory more definitively.

Bigger than what killed the dinosaurs

But if true, the team's crater would be several times larger than the one associated with killing off the dinosaurs, which was 120 kilometers wide.

Although, Robert's object would have not carried the same consequences – anything that would have hit the Earth 2.1 billion years ago would only have affected life at the bacterial level – the theoretical Quebec crater would dwarf the largest crater known on Earth, the Vredefort crater in South Africa, which is 300 kilometres in diameter.