New research from a planetary scientist at Western University in London, Ont., is providing some clarity on the possible origins and age of a massive impact crater in Greenland.
The 31-kilometre-wide crater beneath the Hiawatha Glacier was first discovered by scientists led by the University of Copenhagen in 2018.
Since its discovery, the crater has sparked a debate about whether the two-kilometre-wide asteroid believed to have made it, hit before or after the Greenland Ice Sheet formed around 2.6 million years ago.
A new research paper from scientist Elizabeth Silber is now suggesting the Hiawatha crater could be young, having formed between 11,700 and 2.6 million years ago.
“It is a rarity to find a new impact crater on Earth, let alone one of this size,” said Silber, an adjunct professor with Western’s department of earth sciences.
“While some 190 impact structures have been catalogued thus far, this putative crater is interesting because it looks geologically young and well preserved and, if confirmed, it will be among the largest ever found on Earth.”
Because the crater was hidden underneath the ice, Silber said the question is if it was formed before or during the ice existed.
“Because it is very well preserved, it points to a possibly very young age, as young as the onset of the Younger Dryas period (between 11,500 and 14,500 years ago),” said Silber. “Alternatively, if old, it tells us about the erosional processes that might have taken place in that area.”
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A team made up of Silber and some of the original researchers used a numerical tool called hydrocode modelling to figure out the physics behind the shockwave, looking at impact speed, surface temperature and other facts.
Silber said an impact of this size should form a peak-ring basin with a pronounced crater rim if an asteroid slams directly into bedrock, whereas the Hiawatha crater rim is less pronounced.
The formation of the central uplift makes sense if an asteroid hit at a time when the land was covered with ice likely 1.5 to 2 kilometres thick, she said.
“The modelling shows that thick overlying ice, in fact, serves to muffle the formation of a peak-ring basin,” said Silber. “Furthermore, the nearby drill cores don’t show any rocky ejecta from the impact, and our study shows that ice sheets inhibit ejection of rocky material during the impact.”
Silber calculated some of the likely after-effects of a large asteroid slamming into the ice sheet resulted in winds of 400 kilometres an hour ripping down trees within a 200-kilometre radius and stripping them of branches and leaves.
She estimates anyone within a 500-kilometre radius would have seen a white-hot fireball that appeared four times larger than the sun.
“From a scientific standpoint, we want to know how something might have occurred and how it might have affected the region. After all, the Chixculub impact, which was significantly larger than the Hiawatha impact, was responsible for wiping out the dinosaurs some 65 million years ago.”
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