Sunday , May 16 2021

Impact of ice age | Science



A great asteroid hit the Greenland in people's time. How did it affect the planet?

A 1.5-kilometer asteroid, in whole or in pieces, may have to break into a ice sheet only 13,000 years ago.

IMAGE: NASA SCIENTIFIC EVIDENT STUDY

On a brilliant day July 2 years ago, Kurt Kjær in a helicopter flew over the north west, which is mostly ice, white and sprayy. Shortly, its target was highlighted: Hiawatha Glacier, a slowly moving leaflet more than a kilometer thick. He moves on Ocean Ocean, not in a straight wall, but in a clear semicircle, as if it were breaking out a basin. Kjær, a geologist at the Museum of Natural History of Denmark in Copenhagen, suspects that the glacier hides an explosive secret. The helicopter lands near the river that grows drainage and glaciers, sweeping rocks below. Kjær was given 18 hours to discover the mineral crystals that would confirm his suspicions.

What brought home he remembered the case for a great discovery. Hidden under Hiawatha is a 31-kilometer effect grater, large enough to swallow Washington, D.C., Kjær and 21 co-authors reporting this week in a paper in Science Feedback. The crater was left when there was a 1.5km iron asteroid across the Earth, possibly in the last 100,000 years.

Although it was not as cataclysmic as the dinosaur-shock Chicxulub effect, which was a 200-kilometer wide crater in Mexico about 66 million years ago, the Hiawatha impactor may have left an edition on the history of the planet. The timing is still to be debated, but some researchers on the discovery team believe that the asteroid hit at a crucial time: about 13,000 years ago, just like the world abolished from & Last night yesterday. That would mean it falls to the Earth when other mammals and megafauna deteriorated and people spread throughout North America.

The effect would have been glasses for anyone within 500 kilometers. A white fireball would be four times larger and three times brighter than the sun had flourished across the air. If the object hit an ice sheet, it would be tied to the fund, evaporating water and stones alike in a flash. The resulting explosion packed the energy of 700 1-megaton nuclear bombs, and even a hundred kilometers away observer has experienced a buffet shock wave, sandy waves, and a wind turbine winds. Later, rock debris could have rained down on North America and Europe, and the release of steam, greenhouse gas, was warmed up by local Greenland, melting even more ice.

The news about the impact discovery has re-analyzed an old argument among scientists who are studying an ancient climate. A huge effect on the ice leaflet would have discharged melt water into the Atlantic Ocean – which could interfere with the carrier belt of ocean currents and cause tightening temperatures, especially in the North Hemisphere. "What would it mean for species or life at the time? It's a huge open question," said Jennifer Marlon, paleoclimatologist at Yale University.

A decade ago, a small group of scientists proposed a similar scenario. They tried to explain a cooling event, over 1000 years long, of the name Dryas Young, which began 12,800 years ago, as the last ice age ends. Their controversial solution was the demand of an outreach agent: the effect of one or more comedy. The researchers, as well as changing the North Atlantic plumbing, proposed that the effect was also wild fires across two continents that led to the disappearance of large mammals and the disappearance of Clovis people who were hosting mammoths from North America. The research group organized suggestive but unexpected evidence, and a few other scientists who were convinced. But the idea still held the public's imagination despite a clear constraint: Nobody could have an effect creator.

The drives of drums Dryas now feel really. "I would inevitably anticipate that this crater is the same age as the Youngest Dryas," said James Kennett, a marine geologist at the University of California, Santa Barbara, one of the original developments of the idea.

But Jay Melosh, an impact crater expert at Purdue University in West Lafayette, Indiana, suspects that the strike is so up to date. Statistically, the effect of the size of Hiawatha occurs only every few million years, he says, and so the chances of one just 13,000 years ago are small. Regardless of who's right, the discovery will give the effectors of Youngas Dryas the bullets – and they will turn the defender Hiawatha into another type of projector. "This is hot potatoes," said Melosh Science. "Are you aware that you're going to install a fire explosion?"

USE IT WITH hole. In 2015, Kjær and a colleague were studying a new map of hidden contours under Greenland ice. Based on variations in depth patterns and the surface of the ice surface, the map offered a broad suggestion of the topography of belts – including a hole suggestion under Hiawatha.

Kjær remembered a huge iron meteor at his museum yard, as he parked his bike. Call Agpalilik, Inuit for "the Man," the 20-ton rock is an even larger piece of meteorite, Cape York, found in pieces in the northwestern of the Greenland by Western auditories but long used by Inuit people as an iron source for harpoon tips and tools. Kjær was wondering if the meteorite would be the rest of an exhaust that excavates the circular feature under Hiawatha. But he was still not confident that it was a grater of effect. He needed to see it more clearly with a radar, which can penetrate ice and reflection from a bed rock.

The Kjær team started working with Joseph MacGregor, a glaciar at the NASA Goddard Sailing Center in Greenbelt, Maryland, and heralded archival radar data. MacGregor found that the NASA aircraft often flown over the site on the way to inspect Arctic ice and sometimes the instruments were turned on probation, on the way out. "That was quite glorious," said MacGregor.

The radar images show more clearly what seemed like a crater edge, but they were still too bad in the middle. Many features on Earth's surface, such as volcanic heats, can hide as circles. But there are only bristles and the effects with central copper and peak circles, formed in the center of a newborn crater, when it is similar to stone litter in poolfish rocks conflicts immediately after a strike. To search for those features, the researchers needed a specific radar mission.

Coincidentally, the Alfred Wegener Foundation for Polar and Marine Research in Bremerhaven, Germany, had bought a new penetrating ice-ray radar to create the wings and body of the basler, DC-3 which re-imposes a wing -propelyn that works as an Arctic science. But there was also a need for funding and a base near Hiawatha.

Kjær was looking after the money. Traditional funding agencies would be too slow, or intend to drop their idea, he says. Thus, the Carlsberg Copenhagen Institute, which uses profits from global beer sales to fund science, petitioned. MacGregor, for his part, won NASA colleagues to persuade the US military to let them work out of Base Thule Air, a Cold War station in North Greenland, where German members of the team tried to get permission to work for 20 years. "I was retired, very serious German scientists send me a happy-face emotion," said MacGregor.

Three flights added, in May 2016, 1600 kilometers of fresh data from dozens of transitions across the ice – and evidence that Kjær, MacGregor, and their team were on something. The radar revealed prominent bumps in the center of the crater, identifying a central peak rising about 50 meters in height. And in a sign of recent effects, the bottom of the crater is extremely alarming. If the asteroid had hit earlier than 100,000 years ago, when the area would be free of ice, a erosion of ice that melted into the land would have Cut crater smoothly, said MacGregor. The radar signals also showed that the deep layers of ice were tied up-another sign of recent impact. The wonderful patterns, said MacGregor, suggest that "the ice sheet is not balanced with the presence of this effect crater."

But the team wanted to have direct evidence to overcome the doubts they knew greeting a claim for a huge young grater, which seemed to disrupt the allegations of how often great effects happen. And that's why Kjær himself got himself, on that bright July day in 2016, sampling sturdy rocks along the crescent of the land that surrounds the Hiawatha face. Its most vital detention was in the middle of the semicircle, near the river, where it collected sediment that emerged inside the glacier. It was amazing, he said- "one of those days when you checked your samples, falls on the bed, and you do not get up for a while."

And crater hidden

Under a lobe of ice on the west of the north, air radar and land sampling have revealed a huge and extremely fresh impact crater. Although not as big as the Chicxulub impact of a dinosaur slaughter, the Hiawatha crater may have formed as recently as the end of the last ice age, as people spread across North America. Meltwater of the effect could have triggered a thousand years in the North Hemisphere by interrupting conditions in the Atlantic.

CREDITS: (GRAPHIC) C. BICKEL /SCIENCE; (DATA) HIGHER UMN GEOSPATAL CENTER; ICEBRIDGE BEDMACHINE GREENLAND / NATIONAL NATIONAL NASA AND ICE DATA CENTER

In that leaflet, Kjær's team closed his case. By dipping through the sand, Adam Garde, a geologist in the Denmark Geological Survey and the Greenland in Copenhagen, finds a glass of glass intended at a higher temperature than volcanic combat. More importantly, quartz shock crystals were discovered. The crystals included a distinctive pattern pattern that can only be formed in the intense pressure of out-of-earth effects or nuclear weapons. The quartz makes the case, says Melosh. "It looks pretty good. All the evidence is quite compelling."

Now, the team needs to identify exactly when the collision occurred and how it affected the planet.

Y DRYAS YOUNGER, which has been named after the little white and yellow arctic flowers that have flourished during the cold junk, have long interesting scientists. Until warming up the human-driven global warming, that time was one of the most recent rapid speeds in Earth temperature. As the last ice age has weakened, about 12,800 years ago, temperature in parts of the North Hemisphere was extended by as much as 8 ° C, all the way back to ice age readings. They stayed there for more than 1000 years, turning wood back into dundra.

The trigger could have had an impairment of the sea belt carrier belt, including the Gulf Flow which carries heat to the north of the tropics. In a paper in 1989 in Nature, Kennett, along with Wallace Broecker, a climate scientist at the Earth's Lamont-Doherty Observatory of Columbia University, and others, have indicated how the melting water of growing leaflets could have closed the carrier. As warm water from the tropics goes north on the surface, it is chilled while evaporation makes it easier. Both factors promote the intensity of the water until it sinks to the abyss, helping to drive the carrier. It could add a less intense freshwater pulse to beat the brakes. The Paleoclimate researchers have approved the idea to a large extent, although evidence for such flooding has been flawed until recently.

Then, in 2007, Kennett suggested a new trigger. He joined scientists led by Richard Firestone, a physicist at the Lawrence Berkeley National Laboratory in California, who offered a comet strike at the moment. Spreading over the ice leaflet that covers North America, the comet or comets would have thrown light dust in the air, cooling the region. Further to the south, fuel explosions would have set up forests, producing a thickening barn with a poisoning and cooling. The effect could also have unstable ice and unpublished water water that would have disturbed Atlantic circulation.

Climate disorder, suggested by the team, could explain why Clovis settlements are emptying and that the megafauna disappears soon after. But the evidence was incredible. Firestone and his colleagues underlined tiny sediment layers in dozens of archaeological sites in North America. Those sediments seemed to contain geochemical remains on a huge impact, such as a peak in the iridium, the exotic element which helped to cement the cause for the Chicxulub effect. The layers also produced small beads of glass and possible meteorite debris-and heavy loads of soot and charcoal, identifying fires.

The team met criticism immediately. The decline of mammoths, large rodents, and other species had started well before the Youngest Dryas. In addition, there was no sign of a human man in North America, archaeologists said. Nomadic Clwadis people would not stay long at any site. It is likely that the stunning points that marked their presence did not disappear because the people had died out, but rather because those weapons were no longer useful after the mammal waned, said Vance Holliday, archaeologist at the University of Arizona in Tucson. The impact assumption was trying to solve problems that did not need to be resolved.

Geochemical evidence also starts to erode. External scientists could not find iridium spikes in samples and group. The beads were real, but they were extensive at many geological times, and noisy and charcoal did not appear at the time of Younger Dryas. "All these things were listed that are not enough enough," said Stein Jacobsen, a geometry at Harvard University who is studying a crater.

Again, the assumption never has an effect ever dead. His bidders continued to study the purpose of the purple layer at other sites in Europe and the Middle East. They also reported that finding microscopic diamonds in different sites that could be formed, but they say, are formed by effect only. (External researchers question the allegations of diamonds.)

Now, with the discovery of the Hiawatha crater, "I think we have the gun to smoke," said Wendy Wolbach, a chemistist at the University of South Paul in Chicago, Illinois, who has done work on fires during the period.

The effect would have melted 1500 gigatons of ice, the team estimates-to see as much ice as Antarctica has lost due to global warming in the past decade. The local greenhouse effect of the released steam and residual heat in the crater rock would have added more melting. Much of that freshwater could end in the nearby Labrador Sea, which is the main site pumping the Atlantic Ocean turning circulation. "That could interfere with the circulation," says Sophia Hines, a marine paleoclimatologist at Lamont-Doherty.

The NASA and German aircraft used a radar to see the impact of crater contours under the ice Hiawatha Glacier.

PHOTO: JOHN SONNTAG / NASA

Leery the earlier argument, Kjær will not endorse that scenario. "I do not put myself in front of the bandwagon," he said. But in drafts of the paper, he admitted, the team specifically called for a possible connection between the impact of Hiawatha and the Youngest Dryas.

THE EVIDENCE TAKES with the ice. In the radar images, a shingle of remote volcanic ammunition makes some of the boundaries between seasonal layers standing out as bright reflections. Those bright layers can be matched to the same layers of grit in ice colors dated after cataloging from other parts of the Greenland. Using that technique, the Kjær team found that most ice in Hiawatha had to perfectly fit through the last 11,700 years. But in the older ice, harassment below, the bright reflections disappear. In tracing the deep layers, the team was equivalent to the jumble with the frost of a barn area lying on the edge of Hiawatha previously distributed to 12,800 years ago. "It was quite self-consistent that the ice flow was severely disturbed on or before the Young Dryas," said MacGregor.

Other sources of evidence also suggest that Hiawatha could be the effect of Dryas younger. In 2013, Jacobsen examined a green core from the center of the Greenland, 1000 kilometers away. He expected to put the Younger Dryas effect theory to rest by showing that, 12,800 years ago, the levels of metals that the effects of asteroids tend to spread are not spikes. Instead, a platinum peak was found, similar to those measured in samples of the crater site. "That's suggesting a connection with the Young Dryas there," said Jacobsen.

For Broecker, the co-events combine. The Firestone paper was entertained for the first time, but quickly joined the ranks of keepers. Advocates of the impact of Dryas Ifancaf weigh too much on him, he says: the fires, eradication of the megafauna, give the best to Clovis sites. "They give him a bad brilliance." But Jacoben's top platinum, and then Hiawatha's discovery, was found to have believed it again. "It must be the same," he said.

Yet, no one can be sure of the timing. Harassment layers can not reflect more than normal normal stress in the ice sheet. "We know too well that older ice can be lost by shearing or melting at the bottom," said Jeff Severinghaus, paleoclimatologist at the Scripps Oceanic Institute in San Diego, California. Richard Alley, a glacier at the University of Pennsylvania University at University Park, believes that the effect is far more than 100,000 years and that a lower lake can explain the strange textures near the bottom of the ice. "The ice that flows over growing and burial lakes that interact with rough topography may have produced relatively complex structures," said Alley.

In 2016, Kurt Kjær looked for evidence of the effect of sand washed out under the Hiawatha Realm. He would find glass beads and quartz crystals shock.

PHOTO: SVEND FUND

Recent effects should have left its mark in the half of twelve deep acres and drill at other sites on the Greenland, which records the 100,000 years history of the current ice sheet. Yet no-one shows the layer of thin rubble that Hiawatha's big strike should have kicked. "You should really see something," said Severinghaus.

Brandon Johnson, a planetary scientist at Brown University, is not as sure. After seeing a draft of the study, Johnson used modeling effects on frozen images such as Europa and Enceladus, its code to recreate the effect of an asteroid on a thick ice sheet. The impact of a crater roaming with a central peak is like the one seen in Hiawatha, but here the ice prevents the spread of rocky debris. "The initial results are that it gets far less," said Johnson.

EVEN IF THE ASTEROID hit at the right time, it may not have expired all the disasters anticipated by the youngest Dryas effect. "It's too small and too far to kill the Pleistoccan mammals in the continental United States," said Melosh. And how a strike could spray flames in a cold region, it's so hard to see it. "I can not imagine how something like this could affect this location causing huge fires in North America," said Marlon.

It may not even have triggered the Youngest Dryas. The ocean sediment ponds show that there is no freshwater skin in the Green Sea Labrador, says Lloyd Keigwin, a paleoclimatologist at the Oceanographic Woods Hole Foundation in Massachusetts. The best evidence, he added, suggests flooding into the Arctic Ocean through West Canada instead.

Band patterns in the mineral quartz are diagnostic of shock waves of an extra-earth effect.

IMAGE: ADAM GARDE, GEUS

Alley may not need an external trigger in any case, says Alley. During the last ice age, North Atlantic saw 25 other cooling periods, probably triggered by disrupting the distribution of Atlantic circulation. None of those periods, known as Dansgaard-Oeschger (DO) events, were as severe as Younger Dryas, but their inconvenience suggests that an inner circle plays a role in Young Dryas too . Even Broecker agrees that the effect was not the main cause of cooling. If D-O events represent sudden transformations between two constant states of the sea, he said, "you could say that the sea is approaching instability and somehow that this event has beaten."

Still, Hiawatha's full story will come down to his age. Even an open impact crater can be a challenge for dating, which seeks to procure the moment when the effect changes existing rocks – not the original age of the impairment or target. The Kjær team has been trying. They undermine lasers in the glass spherules to release a cone for dating, but the samples were too contaminated. The researchers explore the blue crystalline of the mineral expression for lines left by the uranium rot, but there is a long arrow. The team also detects the remains of carbon in other samples, which may at some time produce a date, says Kjær. But the ultimate need may require drilling through the ice to the crater floor, to a rock that melts in the effect, replacing its radioactive clock. With large enough samples, researchers should be able to push down the age of Hiawatha.

Given the remote location, a drill to the hole in the world would be expensive. But an understanding of the history of the climate recently – and what a huge impact to the planet can – at stake. "Someone has to go drill there," said Keigwin. "That's all there."


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