Through a mixture of field mapping, rock dating, and geological qualitative analysis techniques, researchers are ready to show that features previously argued to be the faint signature of a long-eroded crater were anything but. The alleged structure is the maximum amount the merchandise of the identical geological processes as people who created the encircling region.
Estimated as being around 3 billion years old, the ricks within the Maniitsoq structure date back the Archean era (4-2.5 billion years ago), a period in Earth’s history that geologists have little solid evidence to travel on when it involves impact craters.
“Our results conclusively rule out the proposal that much of the Archean rock mass within the Maniitsoq region formed by an Archean meteorite impact, which leaves the two.23 Ga Yarrabubba structure in Western Australia because the oldest confirmed terrestrial impact structure,” write the researchers in their published paper.
“The source craters for Archean-aged impact ejecta remain elusive on Earth.”
The idea of Greenland hiding the oldest impact crater on record was first suggests in 2012, but the Maniitsoq site was never widely accepted as being such a crater: even from the beginning, it didn’t meet enough of the mandatory criteria to create it a conclusive discovery.
Ticking all impact crater criteria box should not be required when addressing geological evidence that’s billions of years old, the researchers behind the first proposal argued – rocks can change plenty over such massive periods of your time.
A magnetic anomaly across the location, a central section of pulverized rocks possibly formed by impact shock, unusual quartz structures, and other changes perhaps caused by hot seawater seeping through the cracks caused by the meteorite were imply as signs of an enormous strike.
Closer examination for this latest study revealed the magnetic anomaly disappears at a bigger scale, and along with the pulverized rocks, can be explained by normal geological processes.
What’s more, rocks supposedly melted during the meteorite impact clad to be some 40 million years younger than originally thought.
“I attempt to keep an open mind about everything in science, especially until you see the rocks themselves,” geologist Chris Yakymchuk, from the University of Waterloo in Canada, told Massive Science. “[But] after seeing the rocks, it had been quite ‘huh? These don’t look that different from rocks I’ve seen elsewhere within the world.’”
“So either we missed impact structures everywhere on Earth or this wasn’t one.”
Further investigation showed that there was nothing unusual within the crystal structure of rocks at the Maniitsoq site, and an analysis of 5,587 zircon grains found no evidence of a large shock impacting on the geology of the region. As for the frenzy of hot seawater, a glance at the kind of oxygen isotope on the zircon did not show signs it had ever occurred.
With the Greenland site out of the running, that leaves the Yarrabubba site in Western Australia – dated to 2.229 billion years ago and 70 kilometers (44 miles) wide – because the oldest impact crater discovered thus far.
While the researchers behind the new study admit it’s easier to prove something didn’t happen than to prove something did happen, it now seems virtually certain that the 3-billion-year-old Maniitsoq structure wasn’t created by an enormous meteorite.
“You must take everything together and say, okay, what’s the best explanation for all the features we see? and therefore the simplest explanation is that this can be not a bearing,” Yakymchuk told Massive Science.
The research has been published in Earth and Planetary Science Letters.