Meteorites and comets have captured the public imagination for centuries. They arouse awe when we see them shoot through the night sky – and fear at the thought that maybe, just maybe, one of them will collide with our planet.
After all, scientists believe that a meteor or comet that hit Earth 66 million years ago wiped out the dinosaurs.
Yet that was far from the first great rock to collide with our world. Since 2012, some scientists have embraced the hypothesis published by scientists in the journal Earth and Planetary Science Letters the oldest impact crater on Earth – the geological feature created when a smaller object from space collides with a larger one – was the 100-kilometer-wide Maniitsoq structure in Greenland. If this assumption were correct, it would mean that Earth impacted about 3 billion years ago.
A new study in Earth and Planetary Science Lettershowever, refutes that possibility.
As the authors of the paper explain, many of the features of the Maniitsoq structure that early scientists believed to be an impact crater can be explained by other natural processes. For example, it was originally believed that the magnetic anomaly associated with the crater was evidence of a collision. They also argued that some of the rocks appeared to have been crushed by a major impact and that there were abnormal crystal structures.
However, the new paper notes 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 co-authors behind the article believes that they are not at all uncommon.
“I try to keep an open mind about everything in science, especially until you see the rocks themselves,” Chris Yakymchuk, assistant geology professor at the University of Waterloo in Canada and a co-author of the paper, told Massive Science.[But] after seeing the rocks, it was a bit ‘Huh? These don’t look that different from rocks I’ve seen elsewhere in the world. So either we were missing impact structures all over Earth, or this wasn’t one. “
He also pointed out that there are features often associated with impact craters that are absent from the Greenland structure.
“All normal criteria used to evaluate impact structures, especially the zirconium microstructures, were all absent,” explains Yakymchuk. “You have to take it all together and say, okay, what’s the simplest explanation for all the functions we’re seeing? And the simplest explanation is that this is no 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. The Yarrabubba structure is believed to be 2.23 billion years old.
“To date no diagnostic evidence of impact-related deformation has been presented, and in addition, the geological features in the area are consistent with existing models of regional endogenous [non-impact] processes’, the authors concluded in their paper.
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