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Full Version: Supposedly oldest impact crater on Earth isn't a crater after all
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https://massivesci.com/articles/greenlan...-mistakes/

The story of science is filled with errors. But often, we only hear about science in a smooth, streamlined way that removes the countless mistakes and accidents that inevitably happen. We wanted to hear about the unvarnished, goofed-up version of science we don't hear about. This is Mistakes Month.

EXCERPTS: It was a great story. The authors of a 2012 study proposed that 3 billion years ago – before multi-cellular life appeared on Earth – a giant meteorite plummeted through the atmosphere. It punched through the Earth’s surface into the deep crust in what is now west Greenland. Massive heat generated on impact instantaneously melted rocks in a 50 km radius. Earthquakes shook the surviving rocks so violently that they were pulverized beyond recognition. The Earth’s mantle melted and magmas surged up into the impact zone. Meanwhile, from above, seawater poured into the crater and changed the chemical composition of the screamingly hot rocks.

[...] The resulting article was met with widespread media attention, with headlines like "Earth's oldest impact crater found in Greenland." It presented fifteen lines of evidence. None of them were evidence normally used to recognize impact craters by the scientific community, such as shatter cones or planar deformation features in minerals, which are shock damage to rocks and minerals that can only be the result of a high-velocity impact meteorite impact. But, the authors argued that after 3 billion years of erosion, the deep level of crust now at the surface would preserve different features than more recent impacts.

[...] If this was true, it would be by far the oldest recognized impact crater on Earth – more than 800 million years older than the next oldest, the Yarrabubba crater in Western Australia – and it would give us a window into studying the ancient impacts that shaped the early history of Earth.

So, as an international group of geologists from Greenland, Denmark, Canada, and Australia, embarking on making a modern geological map of this same region, we were eager to see these remarkable rocks. But when we did, we were surprised to find that they looked like many other ancient rocks we had worked on in other parts of the world with no particularly unusual features that would obviously suggest an impact.

Chris Yakymchuk, assistant professor at the University of Waterloo and lead author of our new study evaluating the meteorite impact model, explains his first reaction: "I try to keep an open mind about everything in science, especially until you see the rocks themselves. [But] after seeing the rocks, it was kind of 'Huh? These don't look that different from rocks I’ve seen elsewhere in the world.' So either we missed impact structures everywhere on Earth or this wasn't one." (MORE - details)