(CN) — The crater is a staggering 20 miles wide and buried under more than half a mile of Greenlandic ice, placing it among the largest meteorite impact sites known to exist on Earth. Many experts previously believed the impact caused the Younger Dryas, a nearly 1,000-year-long period of global cooling that began 13,000 years ago.
That no longer appears to be the case, however, as scientists performed tests on sand and rock samples retrieved from the site to determine the true age of the impact. They show the event likely occurred 58 million years ago during the late Paleocene, long before humans began to populate the Earth, and far too long ago to have kicked off the Younger Dryas.
Teams of researchers from Denmark and Sweden worked together to unravel the mystery of the Hiawatha impact crater, first discovered in 2015 in northwestern Greenland, which they describe in a new study published Wednesday in the journal Science Advances.
“The Hiawatha impact structure, the first known impact structure under the Greenland Ice Sheet, formed 58 million years ago, far before the formation of the ice sheet, 2.6 million years ago,” said co-author Dr. Gavin Kenny, a scientist in the Department of Geosciences at the Swedish Museum of Natural History in Stockholm, in an email. “Thus, the impact did not happen — or cause a climate change event — in the time of humans, as had been proposed and speculated previously.”
The authors say this new evidence will help with further investigations into the impact’s possible effect on climate change during an important time in Earth's geologic history.
“The new age for the impact structure opens the door to finding a record of the impact in sedimentary rocks of this age, which allows us to understand the precise effects of the impact on the regional, and potentially global, climate,” Kenny said.
Researchers from the Natural History Museum of Denmark analyzed samples of sand taken from the site by heating them with a high-powered laser until they released argon gas, which they tested to determine the age of the samples. Meanwhile, their counterparts at the Swedish Museum of Natural History tested related rock samples using a uranium-lead dating technique performed on the mineral zircon. After both analyses were complete, the teams compared notes and discovered they had arrived at approximately the same timeframe for the impact using two distinct methods.
The meteorite that caused the Hiawatha impact is now believed to have struck 8 million years after the Chicxulub impact in present-day Mexico which caused a devastating worldwide climate disaster leading to the extinction of the dinosaurs. Despite being much smaller than the 125-mile-wide Chicxulub crater, the Hiawatha crater is still believed to have devastated the region where it struck and may have affected plant and animal life outside the impact zone.
Back then Greenland wasn’t the frozen landmass that it is today — at the time of the impact the island was covered in rainforest and home to numerous animal species, with air temperatures believed to average around the mid-60s. The Hiawatha asteroid strike changed all that, releasing millions of times more energy than an atomic bomb, and drastically altering the local landscape.
According to Kenny, researchers are continuing their work on samples retrieved from the crater during field trips to the area. He said the new age for the crater means researchers around the world will now have a better idea of which rocks to search for evidence for ejecta from the impact to test what, if any, affect the asteroid strike had on the global climate. He acknowledges there isn’t any direct evidence to support such an affect as of yet.
“I think this study is a nice example of science correcting itself. Just a few years ago, when the structure was first discovered and proposed as an impact crater, one logical explanation was that the crater formed since the formation of the ice sheet 2.6 million years ago. But further work showed that this was not correct. The crater is much older,” Kenny explained. “I think it is a nice example of scientists not having an agenda, but simply trying to get to the truth. Often that means acknowledging that one didn’t get it quite right last time around!”
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