An international team of scientists has discovered in Greenland the Earth’s oldest known impact site.
Reporting in Earth and Planetary Science Letters, the researchers concluded that a 60 mile wide crater near the Maniitsoq region of West Greenland is the result of a massive asteroid or comet impact three billion years ago.
The previously oldest known crater on Earth, the 186 mile wide Vredefort crater in South Africa, formed 2 billion years ago and is heavily eroded. Chances of finding an even older impact were thought to be, literally, astronomically low.
Now, a team of scientists from Cardiff, the Geological Survey of Denmark and Greenland (GEUS) in Copenhagen, Lund University in Sweden and the Institute of Planetary Science in Moscow has upset these odds.
“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,” Iain McDonald of the School of Earth and Ocean Sciences, who was part of the team, said.
Finding the evidence was made all the harder because there is no obvious bowl-shaped crater left to find.
Over the 3 billion years since the impact, the land has been eroded down to expose deeper crust 16 miles below the original surface. All external parts of the impact structure have been removed, but the effects of the intense impact shock wave penetrated deep into the crust — far deeper than at any other known crater — and these remain visible.
However, because the effects of impact at these depths have never been observed before it has taken nearly three years of painstaking work to assemble all the key evidence.
“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,” said McDonald.
Only around 180 impact craters have ever been discovered on Earth and around 30 percent of them contain important natural resources of minerals or oil and gas.
“It has taken us nearly three years to convince our peers in the scientific community of this but the mining industry was far more receptive,” McDonald said.
“A Canadian exploration company has been using the impact model to explore for deposits of nickel and platinum metals at Maniitsoq since the autumn of 2011,” he added.
Adam A. Garde, Iain McDonald, Brendan Dyck, Nynke Keulen. Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland. Earth and Planetary Science Letters, 2012; 337-338: 197 DOI: 10.1016/j.epsl.2012.04.026