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

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

A devastating meteorite impact on Greenland discovered in 2018 has not occurred sometime in the past 2.6 million years, as previously thought. No, it happened 58 million years ago. Scientists infer this after dating rock grains near the impact crater. they The results were published on Wednesday at science progress

The impact crater discovery, in northern Greenland, was described in 2018 in the same journal, By roughly the same group of scientists† On the basis of radar images, they detected a depression 31 km wide and 300 m deep in the landscape under an ice sheet about 1 km thick. Unable to reach under the ice, they searched a few miles to the northwest for more evidence of meteorite remains and rocks “distorted” by the impact. They chose this site because there is no ice there (the boundary of the ice sheet on the western edge of the depression) and because it is part of the floodplain into which water and sediment flow from the depression.

Researchers are doing field work where the ice cap ends.
Shafaqat Abbas Khan Pictures

mysterious period

They found, among other things, shocked quartz (quartz crystals deformed under high pressure and temperature) and the remains of an iron-rich meteorite. They didn’t have much to go on at the time to get an accurate history of the impact. They estimate that the meteorite impacted sometime in the past 2.6 million years. Perhaps this was the long-awaited cause of the Younger Dryas (12700-11560 years ago), the mysterious period after the last ice age when the climate was just as cold.

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In the research now published, geologists have performed accurate dating, based on isotope measurements on rock grains. They used two different methods, performed at two different sites, in a laboratory in Copenhagen and Stockholm. According to geologist Claudia Kuiper of the Free University, who was not involved in the study, the study was carried out “with extreme caution.” “Researchers have a huge amount of evidence to link the collected material to the effect,” said Kuiper, who specializes in the dating techniques used. She used it herself, among other things, to determine when Chicxulub crater in the Gulf of Mexico formed. Bottom line: 66 million years ago. With the impact of the meteorite, the era of the dinosaurs ended.

It is a relief that we now have a fixed date

Nikolai Krug Larsen Geologist

Nicolaj Krog Larsen, who coordinated the now-published study, says the impact on Greenland “released 1,000 to 10,000 times less energy than the Chicxulub effect.” The Quaternary geology professor at the University of Copenhagen has not yet been able to determine if the impact on Greenland had any consequences for the climate, possibly causing a (local) extinction wave. “We’re looking into it.”

Kuiper thinks it’s great that the same group of researchers is now radically modifying their idea of ​​impact history. “This is how science works.” Larsen says they were “surprised” to find that the crater from the eruption turned out to be 58 million years old, not 2.5. “It is a relief that we now have a fixed date.”

The Meteorite Impact on Greenland became official after it was first published in 2018 Registered in the impact crater database† The site still mentions the date of the impact: 0.0117 to 2.6 million years ago. Larsen: “I don’t know how many times they’ve updated this site.”

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