A giant crater left by the impact of a 30-kilometer asteroid three billion years ago was found in western Greenland by a joint team of Russian and EU researchers.

The crater was first discovered in 2009 by geologist Adam Garde who found structural anomalies in rock formations near the town of Maniitsoq, according to an article to be published in Earth and Planetary Science Letters.

However, it took researchers three years to establish that the crater was left by a celestial body and not volcanic activity.

Three billion years of ongoing geological processes wiped away most traces of the impact near Maniitsoq, but the rock anomalies remained, waiting for the researchers to study them.

The crater is 100 kilometers in diameter but under different circumstances the impact trace could have spanned up to 600 kilometers, the study said.

The Earth's largest impact crater, Vredefort in South Africa, is 300 kilometers in diameter. At two billion years, it was also the oldest until the new discovery. Chicxulub Crater in Mexico, believed to be the trace of the asteroid that killed the dinosaurs 65 million years ago, is 170 kilometers in diameter.

The impact of a 30-kilometer asteroid can evaporate an average country and even trigger a new mass extinction event, killing all higher life-forms, geologists said.

Quelle: RIA

Update: 30.06.2012:

The so far oldest (i.e. 2975 million years) impact crater on Earth was found near Maniitsoq (in “my days” - and in Danish - known as Sukkertoppen) in West Greenland. It is the fourth multi-ring crater discovered on Earth, besides Chicxulub, Sudbury, and Vredefort. It is a 100 km-scale, circular structure in the Archaean North Atlantic Craton centred at 65°15′N, 51°50′W near the Maniitsoq town in the Qeqqata municipality in West Greenland. The structure comprises a set of highly unusual geological features that were created during a single event involving intense crushing and heating and are incompatible with crustal orogenic processes. The presently exposed features of the Maniitsoq structure were buried 20–25 km below the surface when this event occurred at about 3000 million years ago, during waning convergent orogeny. These features include: a large aeromagnetic anomaly; a central 35×50 km² large area of comminuted quartzo-feldspathic material; regional-scale circular deformation; widespread random fractures with featherlike textures; intense fracture cleavage; amphibolite–granite-matrix breccias unrelated to faulting or intrusions; formation and common fluidisation of microbreccias; abundant evidence of direct K-feldspar and plagioclase melting superimposed on already migmatised rocks; deformation of quartz by slip; formation of planar elements in quartz and plagioclase; and, emplacement of crustally contaminated ultramafic intrusions and regional scale hydrothermal alteration under amphibolite-facies conditions. The diagnostic tools employed to identify impacting in the upper crust are inadequate for structures preserved deep within the continental crust. Nevertheless, the inferred scale, strain rates and temperatures necessary to create the Maniitsoq structure rule out a terrestrial origin of the structure.

Finding sufficient evidence was extremely hard 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 25 km 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. 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. Only around 180 impact craters have ever been discovered on Earth and around 30% of them contain important natural resources of minerals or oil and gas. The largest and oldest known crater prior to this study, the 300 kilometre wide Vredefort crater in South Africa, is 2 billion years in age and heavily eroded. It has taken Adam Garde and his co-workers nearly three years to convince their peers in the scientific community that this is an impact structure, while the mining industry was far more receptive. 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.

Quelle:
Adam A. Garde et al.
Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland
Earth and Planetary Science Letters
Volumes 337–338, 1 July 2012, Pages 197–210
http://dx.doi.org/10.1016/j.epsl.2012.04.026