Scientific detective work has discovered the oldest known impact site in the world. The 100km (60 mile) wide scar in Greenland was caused when a large asteroid or comet collided with the Earth three billion years ago.
The previous oldest known crater, in South Africa, was blasted out of the planet a billion years later. Remains of the new-found impact site have stayed hidden before because the bowl-shaped crater was eroded away by weathering and land movement.
It was identified by an international team including Dr Iain McDonald of Cardiff University’s School of Earth and Ocean Sciences. Their work was funded partly by the Danish Carlsberg Foundation set up by the family that runs the famous brewery.
The Solar System came under intense bombardment between three and four billion years ago when it was still a cosmic building site. The Moon still shows a battered face covered with craters from those impacts because there have been no forces to erode them.
Discovery of the crater has drawn a Canadian mining company to the site at Maniitsoq, West Greenland, because of the possibility that the asteroid deposited valuable metals such as nickel and platinum.
The discovery team carried out three years of painstaking work to check their asteroid impact theory. The land has been eroded to much deeper crust, but they found the effects of the impact’s shock wave remain visible.
Dr McDonald said: “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. The process was rather like a Sherlock Holmes story. 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.”
Only around 180 impact craters have ever been discovered on Earth and around 30 per cent of them contain important natural resources of minerals or oil and gas. The previous oldest known crater was the 300km (186 mile) wide Vredefort crater in South Africa, which is heavily eroded after two billion years.
A paper by the scientists from the Geological Survey of Denmark and Greenland (GEUS), Cardiff University in Wales, Lund University in Sweden and the Institute of Planetary Science in Moscow, has just been published in the journal Earth and Planetary Science Letters.