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Did a comet collide with the Earth 13,000 years ago, just as the world was emerging from the last Ice Age, sending it back into a thousand-year-long period of freezing temperatures and darkness?

That is the core idea behind a controversial scientific theory that has emerged in recent decades, known as the Younger Dryas impact hypothesis. The Younger Dryas is the name given to this anomalous period where warming after the last glacial maximum mysteriously and suddenly reversed for a millennium around 10,800 BCE.

The Younger Dryas impact theory shot into the public’s consciousness after alternative history author Graham Hancock covered it in detail in his 2015 book Magicians of the Gods, in which he also took the controversial theory a step further, suggesting that this impact may also have erased evidence for an advanced civilization in humanity’s deep past. As he writes on his website:

The result was a global disaster that lasted for 1,300 years. It is, I believe, the “smoking gun” that made us a species with amnesia and wiped out almost all traces of a former high civilisation of prehistoric antiquity. But there were survivors, who preserved at least some of the knowledge of the civilisation that had been destroyed with the intention of transmitting it to future generations, so it is not an accident that the first traces of the re-emergence of civilisation, in the form of the earliest known megalithic architecture and the re-promulgation of agricultural skills, occur at Gobekli Tepe in Turkey 11,500 years ago — a date that coincides exactly with the end of the Younger Dryas and the return to a more congenial global environment. Everything we have been taught about the origins of civilisation occurs AFTER 11,500 years ago — in other words AFTER the radical punctuation mark of the Younger Dryas. It is what happened before that we desperately need to recover.

While the Younger Dryas impact theory has remained on the fringes of orthodox science over the years, tantalising clues supporting it have been emerging recently, such as a study finding that a comet impact 13,000 years ago set fire to 10% of the planet, and two other pieces of research that suggested a catastrophic extraterrestrial impact event occurred 13,000 years ago.

A New Crater

But now, the smoking gun perhaps might have been found. A new study, published today in Science Advances under the title “A large impact crater beneath Hiawatha Glacier in northwest Greenland“, provides concrete evidence of a previously unknown ancient extraterrestrial impact event that ranks in the top 25 ever discovered. And what’s more, many of the researchers involved believe that it may be the impact that explains the Younger Dryas anomaly.

The reason the crater had previously been undiscovered is that it lies beneath the ice sheet in Greenland. It was only first recognized in 2015, when Dr. Kurt Kjær, a geologist at the Center for GeoGenetics at the Natural History Museum of Denmark (and lead author of the new study) was analyzing a NASA map of Greenland with a colleague when they noticed an enormous circular depression on the Hiawatha Glacier at Greenland’s northwest tip.

Dr. Kjær’s mind unconsciously made an instant connection, with the image of a large meteorite on display in the courtyard near his office in Copenhagen immediately coming to mind. That meteorite, called Agpalilik (Inuit for “the Man), is a 20-ton fragment of an even larger meteorite, the Cape York, parts of which have been ‘found’ by Western explorers in the last century, though they have previously been used by Inuit people as a source of iron for harpoons.

Ahnighito fragment of the Cape York meteorite

A fragment of the Cape York meteorite (‘Ahnighito’, or ‘The Tent’)

While he initially laughed at the idea, Dr. Kjær and his colleague quickly realized that there might be something to it. “There’s only so many ways you could create a circular feature beneath an ice sheet,” he told the New York Times.

After further research, he and his team spent three days in May 2016 flying over the crater using ice-penetrating radar, to map the hidden structure. Their initial suspicion was confirmed, with the aerial survey revealing a huge pit with an elevated, circular rim and raised structures in the center – telltale signs of an impact crater.

And it was massive: nearly 1,000 feet (300 metres) deep and 20 miles (31 km) in diameter, caused by a comet or asteroid that was likely close to a mile in diameter (1.5 km).

Further confirmation came with sediment samples collected from the floodplain below – high concentrations of minerals like nickel and platinum, and pieces of highly shocked quartz, indicated an iron meteorite impact.

A Controversial Date

And while the New York Times article seems to assiduously avoid the dating of the impact, only saying the team “cannot establish an accurate date for the impact, beyond saying it occurred during the Pleistocene” (due to not yet collecting ejected material), a wonderfully detailed write-up of the new research in Science reports that, despite this, many of the researchers involved do have an opinion on when it happened: and that date corresponds with the Younger Dryas impact theory date of 12,800 years ago.

The timing is still up for debate, but some researchers on the discovery team believe the asteroid struck at a crucial moment: roughly 13,000 years ago, just as the world was thawing from the last ice age.

…The impact would have been a spectacle for anyone within 500 kilometers. A white fireball four times larger and three times brighter than the sun would have streaked across the sky. If the object struck an ice sheet, it would have tunneled through to the bedrock, vaporizing water and stone alike in a flash. The resulting explosion packed the energy of 700 1-megaton nuclear bombs, and even an observer hundreds of kilometers away would have experienced a buffeting shock wave, a monstrous thunder-clap, and hurricane-force winds. Later, rock debris might have rained down on North America and Europe, and the released steam, a greenhouse gas, could have locally warmed Greenland, melting even more ice.

The fact that many of the researchers appear to be endorsing the ‘fringe’ Younger Dryas impact theory has already set alarm bells ringing in orthodox circles. “This is a hot potato,” Jay Melosh, an impact crater expert at Purdue University told Science. “You’re aware you’re going to set off a firestorm?” Melosh doubts the suggested impact dating, though his reasoning seems a little forced: statistically, he says, impacts the size of Hiawatha occur only every few million years, and so the chance of one just 13,000 years ago is small.

Nevertheless, Science covers the controversy fairly, and in detail:

The news of the impact discovery has reawakened an old debate among scientists who study ancient climate.

…A decade ago, a small group of scientists proposed a similar scenario. They were trying to explain a cooling event, more than 1000 years long, called the Younger Dryas, which began 12,800 years ago, as the last ice age was ending. Their controversial solution was to invoke an extraterrestrial agent: the impact of one or more comets. The researchers proposed that besides changing the plumbing of the North Atlantic, the impact also ignited wildfires across two continents that led to the extinction of large mammals and the disappearance of the mammoth-hunting Clovis people of North America. The research group marshaled suggestive but inconclusive evidence, and few other scientists were convinced. But the idea caught the public’s imagination despite an obvious limitation: No one could find an impact crater.

Proponents of a Younger Dryas impact now feel vindicated. “I’d unequivocally predict that this crater is the same age as the Younger Dryas,” says James Kennett, a marine geologist at the University of California, Santa Barbara, one of the idea’s original boosters.

…”Now, with the discovery of Hiawatha crater, “I think we have the smoking gun,” says Wendy Wolbach, a geochemist at De-Paul University in Chicago, Illinois, who has done work on fires during the era.

But the researchers are relying on more than wishful thinking when it comes to confirmation of the dating, as there are multiple lines of evidence already supporting it:

  • The crater bottom is exceptionally jagged – if it occurred much earlier it is likely the bottom would be smoother due to the erosion from melting ice.
  • One previously drilled ice core in Greenland shows a spike in platinum about 12,900 years ago.
  • The aerial radar survey also showed that most of the ice in Hiawatha is perfectly layered through the past 11,700 years – but in the deepest layers the ice is disturbed and jumbled together. Furthermore, the team matched the jumble with debris-rich surface ice on Hiawatha’s edge that was previously dated to 12,800 years ago. “It was pretty self-consistent that the ice flow was heavily disturbed at or prior to the Younger Dryas,” one researcher notes.

However, lead researcher Kjær is tip-toeing around the controversy. “I’m not putting myself in front of that bandwagon,” he told Science, while admitting that his team had “explicitly called out a possible connection between the Hiawatha impact and the Younger Dryas.”

However, other researchers remain skeptical that this is the smoking gun for the Younger Dryas impact theory. Jennifer Marlon, a paleoclimatologist at Yale University, notes that…

It’s too small and too far away to kill off the Pleistocene mammals in the continental United States. [And] I can’t imagine how something like this impact in this location could have caused massive fires in North America.

But perhaps this impact was just one of many across the region as part of one larger event? As Graham Hancock notes, there is a “huge fingerprint spanning North America, Central America, parts of South America, most of Europe and parts of the Middle East as well” – known as the Younger Dryas Boundary Field, in which “the tell-tale traces of multiple impacts by the fragments of a giant comet have been found”.

While the debates will go on, it seems certain that this new comet impact discovery will re-energise proponents of the idea that the world’s climate was massively disrupted 12,800 years ago by an extraterrestrial cataclysm.

Link: Massive crater under Greenland’s ice points to climate-altering impact in the time of humans

Paper: A large impact crater beneath Hiawatha Glacier in northwest Greenland (PDF)