For the first time an international team of scientists, led from the Natural History Museum of Denmark (University of Copenhagen), has discovered a crater, produced by the impact of a meteorite, under the continental ice of the Earth.
It is located in the northwest of Greenland, hidden by the Hiawatha glacier.
The discovery occurred in 2015 and for three years researchers have worked to verify their discovery, which they have just released in the journal Science Advances.
In the study they explain that the crater measures more than 31 km in diameter, which corresponds to an area as large as the entire metropolitan area of Madrid, and places it between the 25 largest impact craters of our planet.
The crater was formed when an iron meteorite, about a kilometer or 1.5 km wide crashed into that area of GreenlandBut since then it has been hidden under almost a kilometer of ice.
"It is exceptionally well preserved and that is surprising, because the glacier ice is an incredibly efficient erosive agent that would have quickly removed the impact tracks, but that means this crater must be quite young from a geological point of view," explains the Professor Kurt H. Kjær of the Center for GeoGenetics at the Natural History Museum of Denmark.
Between three million years and 12,000 years
Until now it has not been possible to directly date the crater, but its characteristics indicate that it was formed after the ice sheets began to cover Greenland. This indicates that it is only between three million years old and as close as 12,000 years ago, towards the end of the last ice age.
“We are inclined to think that the impact occurred in the most recent part of this time range,” Kjær stresses to Sinc, adding: “Humans may not have seen the impact, but felt its consequences, as a change climate. Hurricane winds and earthquakes would occur within a radius of 500 km around.
The teacher acknowledges that they have tried various radiometric methods to try to date the crater, "but unfortunately the grains used were contaminated."
His team, along with other experts, will continue to study and debate this issue, as well as the possible links between the meteorite collision and some evolutionary change that could be detected in ancient human populations through DNA.
The crater was first discovered in July 2015 when researchers were inspecting the topography behind the Greenland ice sheet.
It was then that noticed a huge circular depression under the Hiawatha Glacier"We knew immediately that this was something special, but at the same time it became clear that it would be difficult to confirm its origin," recalls Professor Kjær.
In the courtyard of the Geological Museum in Copenhagen, next to the windows of the Center for GeoGenetics, a 20-ton iron meteorite is found recovered in northern Greenland, not far from the Hiawatha Glacier. "It was not very difficult to deduce that the depression could be a meteorite crater not previously described, although initially we had no evidence," says co-author Nicolaj K. Larsen, a professor at Aarhus University.
The powerful ice radar of an airplane
To confirm their suspicions, the team dispatched a German research aircraft from the Alfred Wegener Institute, for fly over the Hiawatha glacier and map the crater and the ice that covered it, with a powerful new ice radar.
Joseph MacGregor, a NASA glaciologist involved in the study, comments: “Previous radar measurements of this glacier were part of a long-term NASA study to map Greenland's changing ice cover. What we really needed to test our hypothesis was an exhaustive radar survey focused on that location. "
"Our colleagues at the Alfred Wegener Institute and the University of Kansas did exactly that," he adds, "with a state-of-the-art radar system that exceeded all expectations and recorded the depression in astonishing detail. A distinctly circular rim, central bulge, altered and undisturbed ice sheets, and basal debris. It was all there ”.
During the summers of 2016 and 2017, the team returned to the area to map tectonic structures in the rock near the foot of the glacier and collecting samples of sediment carried from the depression through a meltwater channel.
“Some of the 'washed' quartz sand from the crater had planar deformation characteristics (planes arranged in parallel in glassy materials) indicative of a violent impact, and this is conclusive proof that the concavity under the Hiawatha Glacier is a crater meteorite ”, emphasizes Professor Larsen.
Previous studies have shown that large impacts can profoundly affect Earth's climate, with important consequences for life on our planet after the collision. An example is the one that wiped out the dinosaurs. Therefore, the authors consider it important to investigate when and how this crater occurred.
“The next step will be to date it exactly”Insists Kjær, who concludes:“ It will be quite a challenge, because it will probably be necessary to recover the material that melted in the lower part of the structure, but the results will be crucial for understand how the impact of Hiawatha affected life on Earth”.
Kurt H. Kjær, Nicolaj K. Larsen, Joseph MacGregor et al. "A large impact crater beneath Hiawatha Glacier in northwest Greenland". Science Advances, November 2018. DOI: 10.1126 / sciadv.aar8173