Radar scans and sediment samples indicate a large meteorite blasted through the ice sheet in Greenland between 3 million and 12,000 years ago. Meteorite hits are difficult to find on Earth because the atmosphere limits the size of space rocks that actually crash, and erosion and rainfall often erase traces of ancient impacts. However, some depressions survive, and researchers have now found one of the largest ever impacts discovered trapped beneath the ice of Greenland’s Hiawatha glacier.
Signs of the crater were first detected by NASA’s Operation Icebridge, an airborne mission that has spent three years using radar to track changes in ice on Greenland’s ice sheet. Researchers from the University of Copenhagen who examined the publicly available data noticed an anomaly underneath the ice of Hiawatha that appeared to be a 19-mile-wide, 1,000-foot-deep crater. If confirmed, it will be one of the top twenty-five largest craters known on Earth and the first to be found under the ice. The researchers also collected sediment samples from channels washing out of the crater, which included bits of shocked quartz that can only be formed during a high-energy impact. They conclude that there is a crater locked beneath the ice, as they reported in their study published in the journal Science Advances.
In a press release at the Center for GeoGenetics at the Natural History Museum of Denmark, lead research author Kurt H. Kjær said, “The crater is exceptionally well-preserved, and that is surprising, because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact … But that means the crater must be rather young from a geological perspective. So far, it has not been possible to date the crater directly, but its condition strongly suggests that it formed after ice began to cover Greenland, so younger than 3 million years old and possibly as recently as 12,000 years ago—toward the end of the last ice age.”
It’s believed to have been a massive global event, that to create the crater, the iron meteor that struck Greenland would have to be half a mile to a mile across and would have had the force of a 700-megaton warhead. Such an impact would have been felt hundreds of miles away, would have warmed up that area of Greenland and may have rained rocky debris down on North America and Europe.
Some researchers believe it could have had an even more significant impact. About 12,800 years ago toward the end of the last ice age, the world was steadily warming up. Then, abruptly, the paleoclimate record shows that temperatures plummeted back to ice age norms for about 1,000 years, a cooling period called the Younger Dryas that has no definite explanation. According to one theory, a comet impact in Greenland would have melted ice and diluted the ocean current that transports warm water through the Atlantic, causing a re-freeze. Some have even suggested such an event could have led to massive forest fires in Europe and North America, leading to the end of megafauna like the mastodon and the human communities that hunted them, which also disappear from the record around this time. “It’s a very speculative idea, but if this does turn out to be [the link], it would have had an outsize impact on human history,” Joseph MacGregor, a glaciologist with NASA, told Brian Clark Howard at National Geographic.