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Meteorites and comets have captured the public imagination for centuries. They inspire awe when we see them shoot across the night sky – and terror at the thought that maybe, maybe, one of them will collide with our planet.
After all, scientists believe that a meteor or comet hitting Earth wiped out dinosaurs 66 million years ago.
Yet it was far from the first large boulder to collide with our world. Since 2012, some researchers have adopted the hypothesis published by scientists in the journal Earth and Planetary Science Letters This oldest impact crater on Earth – the geological feature that forms when a smaller object in space collides with a larger one – was the 62-mile-wide Maniitsoq structure in Greenland. If this assumption were correct, it would mean that the Earth was impacted about 3 billion years ago.
A new study in Earth and Planetary Science Letters, however, refutes this possibility.
As the authors of the article explain, many features of the Maniitsoq structure that early scientists believed to be an impact crater can be explained by other natural processes. For example, the magnetic anomaly associated with the crater was originally considered evidence of a collision. They also argued that some of the rocks appeared to have been shattered by a major impact and that there were abnormal crystal structures.
The new paper notes, however, that the magnetic anomaly can be an illusion and disappears when viewed on a larger scale. As for some of the other supposedly strange rock formations? One of the article’s co-authors thinks they’re not at all unusual.
“I try to keep an open mind on all things science, especially until you see the rocks themselves,” said Chris Yakymchuk, assistant professor of geology at the University of Waterloo in Canada. and co-author of the article, at Massive Science. “[But] after seeing the rocks, it was a bit like “Huh? These are not that different from the rocks I have seen elsewhere in the world. So either we missed impact structures all over Earth or it wasn’t. “
He also pointed out that some features typically associated with impact craters are missing from the structure of Greenland.
“All of the normal criteria used to assess impact structures, especially zircon microstructures, all were missing,” Yakymchuk explained. “You have to take it all together and say, okay, what’s the simplest explanation for all the features we see? And the simplest explanation is it’s not an impact.”
Without the Greenland structure as a hypothetical candidate for the oldest impact crater on Earth, the record now goes to the Yarrabubba structure in Western Australia. Yarrabubba’s structure is believed to be 2.23 billion years old.
“To date, no diagnostic evidence of impact-related deformation has been presented, and furthermore, the geological features of the area are consistent with existing models of [non-impact] process, ”the authors conclude in their article.
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