The world’s oldest meteor impact crater is not a crater at all, scientists say of a new study that suggests natural forces have set the giant indentation in Earth’s surface. But the jury is not there yet.
The wannabe crater, known locally as the Maniitsoq structure, is located 55 kilometers southeast of the town of Maniitsoq in GreenlandThe structure has a diameter of about 100 km and was formed about 3 billion years ago, although its origin has been disputed in recent years.
In 2012, geologist Adam Garde, of the Geological Survey of Denmark and Greenland, and colleagues said they found evidence that the Maniitsoq structure was created by a meteor impact, citing it the earliest known example of its kind. SoilHowever, a new study questions the 2012 team’s findings.
Related: Crash! 10 largest impact craters on Earth
“After an extensive investigation of the Maniitsoq region, we have yet to find evidence of microscopic shock deformation found in almost all other impact craters,” lead author Chris Yakymchuk, a geologist at the University of Waterloo in Canada, told Live Science. “Our data indicates that the structure in the region is the product of antiquity plate tectonics movement, deformation and heating over hundreds of millions of years. “
However, Garde said he is not convinced.
No impact crater?
Garde and his colleagues concluded that the Maniitsoq structure is an impact crater, mainly because of the structure of rocks in the center, they wrote in the magazine in 2012. Earth and Planetary Science LettersThe researchers said the depth of those rocks and the way they were pushed into the ground could only be explained by the impact of a meteorite.
“With the data they had at the time, the origin of an impact was plausible,” said Yakymchuk. “Our goal was to test the impact hypothesis using more data collected from a wider range of techniques.”
Other studies had cast some doubt on the 2012 findings, but Yakymchuk said he and his team came up with an “open mind” about the structure’s origins when they began their study in 2016.
Their main evidence against the origin of an impact comes from an analysis of zircon crystals – extremely durable and tiny structures made up of zirconium silicate. The team analyzed more than 5,000 of these mineral grains and found no evidence – such as fractures in the crystals – that they had been damaged by a powerful impact.
“Zirconia crystals are microscopic time capsules that can absorb the damage caused by shock waves generated during a meteorite impact,” said Yakymchuk. “We found no damage to suggest that ancient shock waves were passing through these minerals.”
Recently, scientists have used these crystals to show that the Earth’s crust was growing rapidly around the same time the Maniitsoq structure was formed, Live Science previously reportedThis kind of tectonic growth spurt likely created the Maniitsoq structure, the researchers said.
Yakymchuk’s team also found a different age for the structure.
“When we started to combine some field observations with data on the age of specific rock units, it started to point us away from the origin of an impact crater,” said Yakymchuk. “The age we retrieved was 40 million years younger than the proposed age of impact.”
The new findings highlight the need to constantly challenge previous studies, which is an important part of the scientific process, Yakymchuk said. “As we develop new scientific techniques and technologies, we are always testing previous hypotheses.”
However, the authors of the 2012 study argue that the new paper doesn’t tell the whole story.
“The most obvious feature of the Maniitsoq structure that requires an alien impact is the central part of the structure,” Garde, lead author of the 2012 study, told Live Science. “I would like to change my interpretation, but I would first of all need a convincing alternative physical explanation.”
Natural geological processes are not enough to explain the structure’s formation, especially in the central regions where rocks appear to have been put under a tremendous amount of force, Garde said.
“Our observations are not discussed in the new study, although they are fundamental,” said Garde.
He also doesn’t think zircon crystals can tell the whole story, because no other proposed impact craters are that old, meaning that the evidence for an impact from the past may have been swept away by geological processes over the course of the eons. Other studies have also shown that surface zirconia crystals can be damaged without visible damage in the crystals, Garde said.
“Yakymchuk et al. Did not study the outer surfaces of the zircons they imaged,” said Garde. “So also when it comes to the zircons, something is missing from their story.”
However, according to the Earth Impact Database, the Maniitsoq structure is no longer recognized as an impact crater. Instead, a study published Jan. 21 in the journal Nature claims that the Yarrabubba impact structure in Western Australia, at about 2.2 billion years old, is now the oldest known impact crater.
The new study was published online March 1 in the journal Earth and Planetary Science Letters.
Originally published on Live Science.