In the mid 2010s, geologists  scanning the surface of Greenland using radar found something strange.

There was a giant hole  underneath the Hiawatha glacier. The hole was more than 300 meters  deep, and 31 kilometers wide, big enough to fit Washington, DC or Paris inside.

So naturally, researchers wanted to  know what made this massive hole, since it could have been erosion,  a volcano, an asteroid impact, or a giant sand worm - you  know, the usual suspects. And it seemed like it might be  connected to another mystery in Greenland that has puzzled  scientists for decades. To solve them both, they needed tiny grains of one of the most common minerals on Earth - quartz. [♪ INTRO] Now before I get back to that  hole, I want to tell you about another weird phenomenon  called the Younger Dryas event.

Between 12,900 years ago and 11,600 years ago, the planet got noticeably colder,  particularly in North America and Europe. This is also when the North American Clovis people disappeared from the archaeological  record, about 12,750 years ago. They were some of the  earliest indigenous Americans, and they’re best known for the  unique stone tools they created.

Now there are a few hypotheses  for why the northern hemisphere suddenly got so cold, including a change  in ocean currents in the Atlantic, or something that just kicked  a lot of dust into the air. The two most likely dust-slingers are a  volcanic eruption or an asteroid impact. And while there was a volcanic  eruption that happened in Germany at around the right time, other  researchers were Team Impact, thinking some space object  must’ve struck the planet.

So when NASA’s Ice Bridge program and  Germany’s Alfred Wegener Institute discovered this hole under Greenland, it seemed like they might’ve found their answer. When they processed their  data, researchers spotted something strange in the  northwestern corner of the country. But to test their hypothesis that  an asteroid made the Greenland hole and caused temperatures to crater  in the process, they needed quartz.

In its pure form, quartz has  a simple structure made from interlocking silicon dioxide tetrahedra,  making tough six-sided prismatic crystals that look great on a bookshelf or in jewelry. And because its structure is so simple  and it’s components are so common, it is found in pretty much  every rock on the planet. And when those bigger rocks erode away, little bits of quartz sand get pushed out, too.

So the researchers investigating  Greenland’s mysterious hole collected the quartz sand washing out  from underneath the Hiawatha glacier, as a way of looking at the  rocks at the bottom of the hole without having to get under  all that ice themselves. And in it, they found quartz grains that bore the telltale signs of a major catastrophe. The grains had PDFs all over them.

And not the document file format. That’s what I thought too. No, they’re planar deformation features, which look like lines scored  across the crystal surface.

These PDFs are a sign that you’re  dealing with shocked quartz, which forms when intense pressure waves knock the internal crystals out of alignment. Shocked quartz is only created  under the kinds of forces that are generated by massive impacts  or immense explosions. Like, nuclear bomb big.

So finding them under Hiawatha was  definitive proof that the hole was a gigantic impact crater, formed when an equally gigantic something crash landed there. The crater’s size suggests it was  formed by an object that was about 1.5 kilometers across - almost twice  the height of the Burj Khalifa in Dubai. A meteorite that large would have  appeared three times brighter than the sun as it streaked across the sky,  and would have hit the Earth with a force of 700 one megaton nuclear bombs.

The impact would have been  powerful enough to vaporize rock, throw debris some 500 kilometers  away, and fill the sky with dust, which would dim the sun and cool the planet. That last bit was what got scientists  excited, because it opened up the possibility that this crater was  connected to the Younger Dryas event. And to figure out if they were right,  they turned to quartz sand once again.

When they examined that quartz sand more closely to date the impact, they were  the ones who were shocked. The Hiawatha crater was not 12,000 years old. It was 58 million years old. ~ So, much to the disappointment of the researchers, that Hiawatha crater could  not explain the Younger Dryas cold snap or the disappearance  of the Clovis people.

But there’s one final twist to this tale,  and it comes thanks to quartz yet again. Other researchers recently discovered  more deposits of shocked quartz at sites all over what is now the eastern US, in the sediment layers that date  to just before the Younger Dryas. There are no craters at these  sites, but the quartz doesn’t lie - there is evidence of a serious explosion.

So scientists think that their  impact hypothesis still has legs, but in the form of an airburst  instead of a collision. The idea is that a massive comet broke  up as it entered Earth’s atmosphere just over 12,000 years ago, and the fragments exploded before they could reach the ground. Those explosions could have  caused mass burning across the North American continent and messed with the climate enough to trigger the Younger Dryas.

There’s still plenty more to learn,  but it looks like the mystery of both the Younger Dryas and the Greenland hole will ultimately have been  solved by regular old quartz. And our Rocks Box subscribers will be  getting their own piece of quartz this month! This mineral may be common, but it’s one of  the prettiest crystals in our collection.

If you’d like to add it to yours,  visit SciShow. Rocks to learn more. Subscriptions reopen today, so if you’re  not already signed up, get on that!

Quartz is a very common mineral, so  we’re either sending exceptionally large or exceptionally clear quartzes. This one’s actually both large and clear. Thanks, Hank.

Wow, I can’t wait to look at  my quartz to see if it shows signs of a cataclysmic, world-changing event. But, hmmmm, how can I do that? Oh!

I have a jeweler’s loupe, which is useful for looking at all kinds of things extra close up. It's like a little magnifying  glass that really magnifies. And we’re now selling SciShow ones.

You can get them at complexly.store  or at the link in the description. They're good for looking at rocks,  but they're also good for looking at just about anything you own. Plant leaves, tiny grains of rice, the  colony of spiders living in your carpet.

Cannot see you though. You're too far away. [♪ OUTRO]