Wednesday , March 3 2021

A huge, previously unknown impact crater found under Greenland ice



A huge, previously unknown impact crater found under Greenland ice

You may not be thinking of huge weight craters that are particularly subtle or in any way hidden from us. If so, you will be surprised by the discovery that this week was published, a 31-kilometer (19-mile) wide crater, for which we did not know it existed.

Let us take important questions from the way – no, the crater is not a home for Godzillo or some kind of Lovecraft horror. It's filled with ice. And so she ran away for so long with our notice.

The crater lies under the Hiawatha glacier in northwestern Greenland. One of the tools used by researchers to monitor the shrinkage of the Greenland ice sheet is to explore radars in the air. The resulting high resolution data shows the shape of the surface of the ice sheet, some of its inner layers, and even the bottom base. In this case, he discovered a suspicious circular depression in ice near the edge of the glacier.

Based on a more detailed radar investigation, the team, led by Kurt Kjær University of Copenhagen, found that this form is not only a coincidence. The basic data showed a crunchy, 320-meter hole depth, along with a slightly raised edge and a central tip. But to confirm that it was a crater, researchers on the ground (or ice) had to get shoes.

Crater location. Panel C shows the surface of the ice measured on the radar. Panel D shows topography under ice. "Src =" https://cdn.arstechnica.net/wp-content/uploads/2018/11/greenland_crater_hiawatha_glacier-2-640x614.jpg "width =" 640 "height =" 614 "srcset =" https: // cdn .arstechnica.net / wp-content / uploads / 2018/11 / greenland_crater_hiawatha_glacier-2-1280x1228.jpg 2x
Enlarge / Crater location. Panel C shows the surface of the ice measured on the radar. On plate D, a topography under ice is displayed.

Buried below 900 m of glacier ice, the hole could not be covered and penetrated directly. But outside the glacial edge, sediments from the glacier base are loaded along the drainage channels – the researchers brought fragments of the crater.

In those sediment granules, researchers found out what they were looking for. There were small pieces of quartz, which had patterned shock patterns, visible in rocks, hit by blows. And there were small particles of glass, too much molten rock, almost instantly chilled. Even the disclosed bases showed tiny defects parallel to the periphery of the crater, which corresponds to the explanation of the impact crater.

Chemistry of sedimentary grains hints at what object the crater created. Compared to the base in the area, the grains contain additional iron, nickel and other elements related to iron meteorites.

According to this, researchers calculated the impact assessment of the impactor. At an estimated speed of 20 kilometers per second, a meteorite with a diameter of about 1.5 kilometers (just under a mile) would make a crater of this size. It would obviously be a violent event (as if a great crater would not turn you away from you).

When?

And that brings us to a million dollars question: when did this happen? It is not the easiest question to answer, and as we will explain at any time, every answer promises to be controversial, so the age study is rather measured.

One of the findings is that the crater drains the channels in the trough. Two channels extend up to the "glacial" side of the crater, which is joined to the right on the rim. One channel is visible on the opposite side of the crater and nothing on the ground of the crater. This means that the channels are probably predefined events, like the street, the pre-date cutout.

Similar drainage channels under other glaciers in the area are supposed to be the source of the river before the Greenland ice sheet became a thing about 2.6 million years ago. But without a better idea of ​​the age of the channels, knowing that the crater is younger than the channels, it does not tell you much about it.

Researchers also tried to analyze the shape of the crater in order to get a rough estimate of the age based on its "freshness". Certain levels of glacial erosion made their age between 5,000 and 50 million years old, which was not quite narrow.

The best guesses of researchers are based on the appearance of ice clustering in radar data. Smooth, bright plastification is visible most of the way down. On the basis of similar work elsewhere, this ice is known to return about 12,000 years ago. Below is a dark layer and chaotic throat at the bottom.

The layer, which is dark on the radar instrument, indicates ice, full of rocks and sediments, which were created during the shorter period of regional cooling known as Young Dryas between 11,700 and 12,800 years. Chaos beneath him is strange and does not appear in radar images outside crater. There you find visually recognizable layers from older periods of time.

Radar images of ice in the crater. "Src =" https://cdn.arstechnica.net/wp-content/uploads/2018/11/greenland_crater_hiawatha_glacier-7-640x734.jpg "width =" 640 "height =" 734 "srcset =" https: // cdn .arstechnica.net / wp-content / uploads / 2018/11 / greenland_crater_hiawatha_glacier-7-1280x1468.jpg 2x
Enlarge / Radar images of ice in the crater.

Researchers explain this that the chaotic ice around the time of the impact – perhaps gliding in the crater, when it was fresh. This would mean the date of the event somewhere between 2.6 million years and 12 000 years ago.

We're back there

This last step is controversial and this becomes controversial. If you want to understand why you need a little foundation in the age of younger trees.

Most studies on the cause of this interesting climate event focused on mechanisms that could hinder the transit of the Atlantic Ocean and halted transport of heat – approximately Tomorrow. Dumping fresh sweet water in the North Atlantic is essentially a way to stumble over this circulation, and many scientists believe that the likely culprit is the sudden release of the accumulated glacial meltwater from Canada.

But this is no certainty; in the last decade, a small group of scientists pushes a very different hypothesis – impact on impact. The scientist's claim has mostly focused on the discovery of alleged influential precipitation at archaeological sites in North America. The problem is that none of these discoveries were supported by other scientists who are studying the same pages. And, of course, there was no crater to suit the account.

It is predictable that this is a small group of scientists terrible I'm interested in this new crater. And since most people in this field believe that the hypothesis of influence is not fully supported – and are further on Really sick of hearing about it – authors of the crater study are in a clumsy situation. Paper allegedly was an unusually rigorous peer review process, with reviewers ensuring that it does not have any casual connections with the Younger Dryas battle. Now, when it was published, there are others already weighing Skepticism.

So, the crater of the blows was formed during the cooling of the younger Dryas? Or is it a few million years older than this? Or is it still older, with researchers misinterpreting the meaning of chaotic ice in it? This will only save additional research. There seems to be no sign of material that was, for example, dug out of the ice cube crater in Greenland, but modeling studies could explain which signals to look for. Obviously, the ice core in the crater would be useful, as could be further examined by the ice on the edge of the glacier, right next to the crater.

Until then, everything we know is that a new crater is added to the map, which is one of the largest in the world. This is an interesting story in itself, but the history of the crater must still be fulfilled.

Science is progressing, 2018. DOI: 10.1126 / sciadv.aar8173 (O DOI).


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