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GREENLAND — Roughly 3 billion years ago, before life on this planet was more extensive than single-celled bacteria, before oxygen had even significantly entered the atmosphere, a gigantic asteroid smashed into the Earth and created a crater 100 km across - as large as the ones you see on the Moon and Mars. And we only just discovered it.
Why did it take us so long to find something so massive? Because 3 billion years ago is a really, really long time and it's mostly gone now due to age and erosion. Being in one of the world's coldest regions, the Maniitsoq region of Greenland, doesn't make studying it any easier either. But scientists from Denmark, Wales, Russia and Sweden braved the cold for three years and are finally convinced that the crater in Greenland is the world's oldest and one of the largest. Only the Vredefort crater in South Africa is larger, at 300 km, but is some 1 billion years younger than the Maniitsoq crater.
"This single discovery means that we can study the effects of cratering on the Earth nearly a billion years further back in time than was possible before," said Dr. Iain McDonald of Cardiff University's School of Earth and Ocean Sciences.
The asteroid that caused this gigantic hole in the ground was roughly 30 km wide, twice as large as the object that created the Vredefort crater. But the direct evidence of the impact has largely been lost to time: The surface showing now was actually 25 km under the surface 3 billion years ago, and hence scientists have had to largely rely on indirect evidence of the impact, such as the structure of nearby quartz and the makeup of the granite rock found at the site.
It has been a long time coming, given the difficulty of piecing together this discovery from such ancient and fragmented remains.
"The process was rather like a Sherlock Holmes story," McDonald said. "We eliminated the impossible in terms of any conventional terrestrial processes, and were left with a giant impact as the only explanation for all of the facts."
There are roughly 180 impact sites visible on the Earth, but all of those were much smaller and much younger. Had there been any kind of life other than bacteria at the time of the Maniitsoq impact, it would almost surely have been obliterated. If such an impact happened now, it would essentially be like hitting the reset button on the game of life on Earth.
