Why is there a 19-mile crater below Greenland?

A city-sized crater hidden beneath a massive ice sheet for centuries has been found in northwest Greenland.

The massive hole is more than 19 miles wide and 300 metres deep, and is believed to have been formed when an iron meteorite smashed into the Earth around three million years ago. If confirmed, it would be the first impact crater ever found under ice, says National Geographic.

The potentially landmark discovery was made by an international team led by researchers from the University of Copenhagen’s Centre for GeoGenetics at the Natural Museum of Denmark. The researchers - who have published a paper about their find in journal Science Advances - chanced upon the crater while examining radar images used to map the topography beneath Greenland’s ice sheets.

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After noticing a circular impact under what is known as the Hiawatha Glacier, the researchers have spent the past three years working out exactly what it might be. They have concluded that it is one of the 25 largest impact craters on Earth, according to a report from Nasa, which was involved in the research.

“The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly remove traces of the impact,” said study author Professor Kurt Kjaer.

In order to confirm the crater’s age, the scientists will have to drill through more than half a mile of ice in order to collect rocks for laboratory dating.

“We would endeavour to do this - it would certainly be the best way to get the ‘dead fish on the table’, so to speak,” Kjaer told the BBC.

Dating the crater’s age would allow scientists to find out if the meteor impact occurred during the last Ice Age, which ended approximately 11,700 years ago.

If so, it could reignite interest in the Younger Dryas impact hypothesis, a theory which suggests that an intense period of cooling at the end of that Ice Age was precipitated by an impact from one or more large comets in North America, says Science magazine.

That suggests the impact of the crater might have impacted the history of the planet.

You can watch Nasa’s video showing how the crater discovery came together here: