Scientists now know the age of a massive crater hidden beneath Greenland’s ice.
Hiawatha crater, which lies under 0.6 miles (1 kilometer) of ice in northwest Greenland, formed 58 million years ago, according to a study published March 9 in the journal. science progress. While some initial estimates put the crater’s age at just 13,000 years, the new discovery means the impact occurred much earlier, at a time when Greenland was brimming with life.
“Greenland was already covered in a temperate rainforest when the asteroid impacted,” said study co-author Michael Storey, a researcher at the Natural History Museum in Denmark who specializes in dating geological materials.
The asteroid It was about 0.9 miles (1.5 kilometers) wide when it hit the ground. It is possible that its effect was triggered locally earthquakes and wildfires, Storey told Live Science, but there is no evidence that they have an effect on global climate.
Scientists The crater was first discovered in 2018, using ice-penetrating radar devices installed on aircraft. But given the massive ice sheet covering the crater, there was no direct way to determine the age of the impact.
Related: In pictures: Hiawatha crater
Fortunately, the crater is located on the edge of the ice sheet. Only 3 miles (5 km) from the crater rim, a stream flows from under the ice, carrying sediment with it. After collecting and examining large grains of sand and gravel from this area, the researchers discovered that many of them showed signs of melting and shocking – indications that they were suddenly and rapidly heated up.
Storey and colleagues used a method called argon-argon dating to characterize the ages of 50 grains of sand from this stream. This method is based on the natural radioactive decay of potassium-40, which is a radioactive variant (or isotope) of the element potassium which has a half-life of 1.251 billion years. Potassium decomposes 40 to argon 40, gas still trapped inside the rock. Researchers can measure the ratio between these two isotopes to determine how long the decay lasted. The very slow rate of dissolution of potassium 40 into argon 40 means that this method is useful for measuring very old ages. The heat of the collision resets this molecular clock to zero, Storey told Live Science, so he and his team can use the numbers to determine when the sand grains collide.
Meanwhile, study co-author Gavin Kenny, a research fellow at the Swedish Museum of Natural History, used a similar method to measure the decay of the radioactive element. uranium Lead is in minerals called zircon that are contained within stream gravel.
Both methods returned similar results: grains and pebbles were subjected to a major impact about 58 million years ago, during the late Paleocene.
This age means that the effect has nothing to do with the Younger Dryas cooling event, a global cold shift that occurred about 13,000 years ago. One controversial theory says that the cooling event was initiated by an asteroid impact, but no crater of the appropriate age has been found.
The deep-ocean sediment cores provided a very detailed record of the climate going back 58 million years, Storey said, and there is no indication that the Hiawatha effect caused any global climatic whirlwind. Storey said the impact would have been devastating to Greenland’s native rainforest flora and fauna. It may have caused a magnitude 8 or 9 earthquake nearby and could have caused massive wildfires. In support of this theory, evidence has been found of ancient coal deposits seeping from under the ice sheets.
“I suspect Hiawatha, on a sliding scale of asteroid impacts, is somewhere in the middle,” Storey said. A space rock the size of the one that created the crater is expected to collide a land Once every 1 to 2 million years, with a 75% chance it will land in the ocean instead of on land.
Now that the age of the crater is known, Storey said, it will be possible to search for sediments of the same age nearby and look for evidence of the consequences.
Originally published on Live Science.
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