In early 2012, an international research team studying parts of southwestern Greenland announced that it had discovered the oldest impact crater ever discovered on Earth, estimated to be 3.3 billion years old. New research now shows that the strange geological feature – known as the Maniitsoq structure – is likely the result of terrestrial geological processes rather than a meteorite impact.
The new study, published this month in Earth and Planetary Science Letters, re-examines some of the evidence from the first 2012 finding. In the middle of the “crater” there is an outcrop of pulverized rock, which the original team interpreted as the central point of impact. However, it turned out that these rocks were igneous rocks formed from cooling lava. In addition, the outcrop was 40 million years younger than originally assumed and almost identical to a similar deposit located a short distance outside the putative impact zone.
The new team also re-examined the deposits of the mineral zircon found at the site. Zircon is geologically resistant over long periods of time. So if it were hit by a meteorite 3.3 billion years ago, it would retain microscopic evidence of shock damage from that event. No such breaks were discovered.
The study’s lead author, Chris Yakymchuk of the University of Waterloo, hoped his expedition could or should not confirm the impact crater hypothesis. “I try to be open to anything in science,” he said, “especially until you see the rocks for yourself. [But] After seeing the rocks it was kind of ‘huh? These don’t look so different from rocks that I’ve seen anywhere else in the world. ‘Either we missed impact structures all over the world or it wasn’t. “
In other parts of the solar system, impact craters are used to determine the ages of the planet’s surfaces. The presence or absence of craters shows how long it has been since a planet or moon was geologically active enough to reappear or pave over its craters. Impact craters, for example, are quickly erased by the volcanic hell landscape of Io, as is the changing and changing ice sheet of Europe.
Like Earth, the young volcanic surface of Jupiter’s moon Io quickly erases evidence of impact craters. Photo credit: NASA (Wikipedia Commons).
The earth is also quite geologically active, which means that impact craters are cleared from the surface fairly quickly (geologically) by plate tectonics, erosion, and volcanism. Most of the craters found on Earth are therefore very new. The oldest confirmed crater (alongside the now unmasked Maniitsoq structure) is Yarrabubba Crater in Western Australia, which is approximately 2.2 billion years old. Any further collision history of our planet is unfortunately lost in time. Or it would be if we didn’t have a conveniently geologically dead neighbor to study: our moon.
The moon carries a record of the solar system’s past that is much deeper in time than the earth. Measurements from the Apollo missions showed that much of the moon’s collision history, and therefore likely Earth as well, happened all at once in a violent event known as the late heavy bombardment, from about 4.1 billion years to 3.8 billion years ago Lasted years ago. During this time, scientists believe that the giant planets migrated outward and diverted objects by gravity from the asteroid belt and Kuiper belt onto collision courses with the inner planets.
The oldest confirmed impact crater on earth is Yarrabubba Crater in Western Australia. It’s 2.2 billion years old. Photo credit: Timmons M. Erickson, Christopher L. Kirkland, Nicholas E. Timms, Aaron J. Cavosie, and Thomas M. Davison (Wikipedia Commons).
After the late heavy bombardment, things calmed down in the inner solar system and life on earth flourished. If it had been real, Maniitsoq Crater would have been a rare example of an impact crater from this quiet period about 3.3 billion years ago. Unfortunately it shouldn’t be.
Julie Hollis, a member of the research team studying the Maniitsoq structure, recalled last week that debunking the impact crater hypothesis for the Maniitsoq structure can be disappointing, but this is just a normal part of the scientific process. “Although … the evidence no longer supports a giant meteor impact, only the original interpretation, not the science itself, is wrong,” she said. “It is a natural part of the scientific process to reject some hypotheses.”
Ancient impact craters on Earth are difficult to pin down for the time being. However, correctly identifying and understanding the geological history of the Maniitsoq structure will help improve our understanding of the history of our planet.
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Selected image source: University of Waterloo
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