The crater under the Greenland ice sheet is much older than expected: 58 million years

A devastating meteorite impact on Greenland discovered in 2018 has not happened in the past 2.6 million years, as previously thought. No, it happened 58 million years ago. Scientists conclude this after dating rock grains near the impact crater. Their the results were released on Wednesday in Scientists progress†

The discovery of the impact crater, in northern Greenland, was described in 2018 in the same journal, by almost the same group of scientists† Based on radar imagery, they discovered a depression 31 km wide and 300 m deep in the landscape under a layer of ice nearly a kilometer thick. Unable to penetrate beneath the ice, they searched a few miles to the northwest for further evidence of the remnants of the meteorite and rock “deformed” by the impact. They chose this site because there is no ice (the edge of the ice sheet is on the western edge of the depression) and because it is part of the floodplain in which water and sediment flows out of the depression.

Enigmatic period

They found, among other things, shocked quartz (quartz crystals deformed under high pressure and temperature) and iron-rich meteorite remains. They had little evidence at the time for an exact dating of the impact. They estimate that the meteorite had an impact within the past 2.6 million years. This may have been the long-sought cause of the Younger Dryas (12,700 to 11,560 years ago), the enigmatic period after the last ice age when the climate cooled just as sharply.

In the newly published research, geologists performed exact dating, based on isotopic measurements on rock grains. They used two different techniques, carried out in two different places, in a laboratory in Copenhagen and in Stockholm. Free University geologist Klaudia Kuiper, who was not involved in the study, said the study was conducted “with great care.” “Researchers have an enormous amount of evidence to link the collected material to the impact,” said Kuiper, who specializes in the dating techniques used. She used them herself, among other things, to determine exactly when the Chicxulub impact crater in the Gulf of Mexico formed. Result: 66 million years ago. With the impact of the meteorite, the age of the dinosaurs came to an end.

It’s a great relief that we now have an exact date

Nicolaj Krog Larsen geologist

Nicolaj Krog Larsen, who coordinated the now published study, says the Greenland impact “released 1,000 to 10,000 times less energy than the Chicxulub impact”. The professor of Quaternary geology at the University of Copenhagen is not yet able to say whether the impact on Greenland had consequences on the climate, and could have caused a wave of (local) extinction. “We are looking into that.”

Kuiper thinks it’s great that almost the same group of researchers are now radically adjusting their own idea of ​​the impact date. “That’s how science works.” Larsen says they were “surprised” to find the impact crater turned out to be 58 million years old, not 2.5. “It’s a great relief that we now have an exact date.”

The impact of a meteorite on Greenland is official after the first publication about it in 2018 recorded in the Impact Crater database† The website always lists the date of the impact: 0.0117 to 2.6 million years ago. Larsen: “I don’t know how often they update this site.”