A large asteroid hit greenland in time for humans. How has it affected the planet? A 1.5-kilometer asteroid, intact or…
A large asteroid hit greenland in time for humans. How has it affected the planet?
A 1.5-kilometer asteroid, intact or in pieces, may have crushed an ice cream just 13,000 years ago.
PICTURE: NASA SCIENTIFIC VISUALIZATION STUDIO
On a bright Christmas day 2 years ago, Kurt Kjær was in a helicopter flying across northwestern Greenland – an ice-filled, pure white and sparkling. Soon his goals came in: The Hiawatha Glacier, a long-term ice plate that is more than a kilometer thick. It moves forward in the Arctic, not in a straight wall, but in an eye-catching semi-circle, as if it is flushed out of a pool. Kjær, a geologist at Denmark’s Natural History Museum in Copenhagen, suspected that the glacier hid an explosive secret. The helicopter landed near the rising river that drains the glacier, sweeping out rocks from below. Kjær had 18 hours to find the mineral crystals that would confirm his suspicions.
What he went home pinched the case for a major discovery. Hidden under Hiawatha is a 31 kilometer long battlefield that is big enough to swallow Washington, D.C., Kjær and 21 co-workers reporting this week in a document in Science Advances . The crater was left when an iron star 1.5 kilometers crossed into the ground, possibly in the last 100,000 years.
But not as catastrophic as the dinosaur-killing Chicxulub impact, which carved out a 200-kilometer crater in Mexico. About 66 million years ago, the Hiawatha slayer has also given a glimpse of the history of the planet. The time is still open for debate, but some scientists on the discovery believe the asteroid hit a crucial moment: about 13,000 years ago, just as the world thrived from the last ice age. This would crash into the ground when mothers and other megafauna were in decline and people spread across North America.
The effect would have been a spectacle for everyone within 500 kilometers. A white fireball four times bigger and three times lighter than the sun would have stretched over the sky. If the object hit an ice sheet it would have thrown through to the bedrock, evaporating both water and rock in a flash. The resulting explosion packed the energy of 700 1 megaton nuclear bombs, and even an observer hundreds of miles away would have experienced a buffering shockwave, a monstrous thunder club and hurricane strength. Later rubbish can have rained down in North America and Europe, and the released steam, a greenhouse gas, could have warmed greenery locally and melt even more ice.
The news of the impact statement has resurrected an old debate among researchers who study old climate. A massive impact on the ice would have sent meltwater that pour into the Atlantic, potentially interfering with ocean currents and causing temperatures to dip, especially in the northern hemisphere. “What would it mean for species or life then?” That’s a huge open question, “said Jennifer Marlon, a paleoclimatologist at Yale University.
For a decade, a small group of researchers suggested a similar scenario. They tried to explain a cooling event, more than 1000 years long, known as Younger Dryas, which began 12,800 years ago, when the last ice age ended. Their controversial solution was to invoke an extraterrestrial means: the effect of one or more comets. The researchers suggested that in addition to replacing plumbing in the North Atlantic, also fires in two continents that led to extinction of large mammals and the disappearance of the mammoth-lingering Clovis people in North America. The research team marched suggestive but insufficient evidence and some other researchers were convinced. But the idea struck the public’s imagination despite an obvious limitation: no one could find a battlefield.
Advocates of a younger Dryas influence now feel they are righteous. “I would unequivocally predict that this crater is the same age as younger Dryas,” said James Kennett, a marine geologist at the University of California, Santa Barbara, one of the original boosters of the idea.
But Jay Melosh, a stroke expert at Purdue University in West Lafayette, Indiana, doubts the strike so recently. Statistically, the size of Hiawatha affects only a few billion years, he says, and the chances are that only 13,000 years ago is small. No matter who is right, the discovery will provide ammunition to Younger Dryas Consequence Theorist – and will make the Hiawatha Impact a different type of projectile. “This is a hot potato,” says Melosh Science . “Are you aware that you are going to start a firestorm?”
IT STARTED WITH a hole. In 2015, Kjær and a colleague studied a new map of the hidden contours under Greenland’s ice. Based on variations in the ice depth and surface flow pattern, the map offered a rough proposal on bedrock topography, including the bucket hole below Hiawatha.
Kjær recalled a massive iron meteorite in the inner courtyard of his museum, near where he parked his bike. Called Agpalilik Inuit of the “man” is 20-tonne stone a fragment of an even greater meteorite, Cape York, found in pieces in northwestern Greenland by western explorers but long used by Inuit people as a source of iron for harpunipsips and tools. Kjær wondered if the meteorite could be a remnant of a percussion that dug the circular function under Hiawatha. But he was still not sure it was a battlefield. He had to see it more clearly with radar, which can penetrate ice and reflect bedrock.
Kjær team started working with Joseph MacGregor, a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, which dug up archival data. MacGregor found that NASA aircraft often flew over the spot on the way to mapping the Arctic Ocean, and the instruments were sometimes smashed, in test mode, on their way out. “It was pretty beautiful,” said MacGregor.
The radar images more clearly showed what looked like the crater, but they were still too fuzzy in the middle. Many functions on the Earth’s surface, like volcanic calendars, can mask as circles. But only craters contain central peaks and top rings, which form in the middle of a newborn crater, when it is like a splash in a dust-melted stone recycling just after a strike. In order to look for these properties, the researchers needed a special radar mission.
The meeting had the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, just bought a next-generation ice-penetrating radar to mount over the wings and body of their Basler aircraft, a twin-propeller retrofitted DC-3 which is a workhorse for Arctic science. But they also needed funding and a base near Hiawatha.
Kjær took care of the money. Traditional funding agencies would be too slow, or inclined to leak their ideas, he thought. Therefore, he asked Copenhagen’s Carlsberg Fund, which uses profits from its global beer sales to finance science. MacGregor, for its part, hired NASA colleagues to convince the US military to train them from Thule Air Base, a cold war post in northern Greenland, where German members of the team had sought permission to work for 20 years. “I had retired, very serious German scientists send me happy face emojis,” said MacGregor.
Three flights, in May 2016, released 1600 kilometers of fresh data from dozens of transits across the ice and evidence that Kjær, MacGregor, and their teams were at something. The radar revealed five prominent bumps in the center of the crater, indicating a central peak rising about 50 meters high. And in a sign of a later impact, the crater is exceptionally tagged. If the asteroid had hit earlier than 100,000 years ago, when the area was ice-free, erosion from melting icecream would crank the crater smoothly, “said MacGregor. The radar signals also showed that the deep ice layers fell apart – another sign of a new impact. The strangely disturbed patterns, says MacGregor, suggest “the ice has not been balanced with the existence of this battlefield”.
However, the team wanted direct evidence to overcome the skepticism that they knew would meet a demand for a massive young crater, one who seemed to defy the odds of how often major consequences occur. Therefore, on the bright Christmas day 2016, Kjær found frenetic sampling of stones along the crescent of the terrain surrounding Hiawatha’s face. His most crucial stop was in the middle of the half circle, near the river, where he collected sediments that appeared to have come from the glacier interior. It was hectic, he says – “one of those days when you just look at your samples falls on the bed and does not rise for a while”.
During an ice-breeze in northwestern Greenland, airborne radar and field sampling have discovered a giant and remarkable fresh battlefield. Although not as big as dinosaur-killing Chicxulub influence, the Hiawatha crater may have formed as recently as the end of the last ice age, when people spread across North America. Meltwater from the impact could have triggered a millennial chill in the northern hemisphere by interfering with currents in the Atlantic.
CREDITER: (GRAPHIC) C. BICKEL / SCIENCE ; (DATA) UMN POLAR GEOSPATIAL CENTER; ICEBRIDGE BEDMACHINE GREENLAND / NASA NATIONAL SNOW AND ICE DATA CENTER
In this surplus Kjar’s team completed its fall. Sighting through the sand found Adam Garde, a geologist at Denmark and Greenland’s geological survey in Copenhagen, glass slides forged at temperatures higher than volcanic eruptions can generate. More importantly, he discovered shocked crystals of quartz. The crystals contained a distinct band pattern that can only be formed in the extreme pressure of extraterrestrial or nuclear weapons. Quartz does the case, says Melosh. “It looks pretty good. All evidence is quite convincing.”
Now the team must find out exactly when the collision occurred and how it affected the planet.
YOUNGER DRYAS named for a small white and yellow arctic flower that flourished under the cold nose, has long fascinated scientists. Before the human power of global warming stood in, it ruled that period as one of the sharpest recent fluctuations in the temperature of the earth. When the last ice age disappeared, about 12 800 years ago, temperatures in parts of the northern hemisphere fell by as much as 8 ° C, all the way back to ice age reading. They stayed that way for more than 1000 years and turned forward in the tundra.
The trigger could have been a disturbance in the ocean currents conveyor, including the Gulf Stream, carrying heat north of the tropics. In a 1989 paper in Nature Kennett collaborated with Wallace Broecker, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory and others, how melt water from returning ice sheet could have closed the carrier. Because hot water from the tropics travels north to the surface it cools while evaporation makes it saltier. Both factors increase the density of the water until it falls into the abyss, which helps to drive the conveyor. Adding a pulse of less dense fresh water can hit the brakes. Paleoclimatic researchers have largely approved the idea, although evidence of such a flood has been missing until recently.
Since 2007 Kennett proposed a new trigger. He collaborated with researchers led by Richard Firestone, a physicist at Lawrence Berkeley National Laboratory in California, who proposed a cardiac strike at the key. Exploding the ice covering North America, the comet or comet would have thrown lightbulb in the sky and cool the region. Further south, elding projectiles would have put woods burning and produced soot that deepened gloomy and cooling. The effect can also have destabilized ice and released melt water that would have overthrowed the atlantic circulation.
The Climate League, the team suggested, was able to explain why the Clovis settlements were emptied and the megafauna disappeared soon afterwards. But the evidence was sharp. Firestone and his colleagues flagged thin sediment layers at dozens of archeological sites in North America. These sediments appeared to contain geochemical traces of extraterrestrial influence, such as a peak in iridium, the exotic element that helped to cement the case of Chicxulub impact. The layers also gave small glass beads and iron-possible meteorite junk and heavy soot and carbon loads, indicating fires.
The team met immediate criticism. The decline of mothers, giant ponds and other species had begun well before Younger Dryas. In addition, there were no signs of a human being in North America, archaeologists said. The nomadic Clovis people would not have stayed for a long time in any place. The distinctive spikes that marked their presence probably did not disappear because the people died but rather because these weapons were no longer useful when the mammals subsided, “said Vance Holliday, an archaeologist at the University of Arizona, Tucson. The power hypothesis tried to solve problems that did not have to be solved.
The geochemical evidence also began to destroy. Outside, researchers could not detect the iridium tip in the group’s samples. The beads were real, but they were abundant over many geological times, and soot and charcoal did not seem like a nail at the time of younger Dryas. “They listed all these things that are not sufficient,” says Stein Jacobsen, a geo-chemist at Harvard University, who studies craters.
But the consequence hypothesis never really died. Its proponents continued to study the supposed garbage layer in other places in Europe and the Middle East. They also reported finding microscopic diamonds in different places that they could have formed solely through an impact. (External researchers question diamonds’ claims.)
Now, with the discovery of the Hiawatha crater, “I think we have the smoke gun,” says Wendy Wolbach, geochemist at DePaul University, Chicago, Illinois, who has been working on fires in the meantime .
The effect would have melted 1500 gigatons of ice cream, estimated to be – about as much ice as Antarctica has lost due to global warming in the last decade. The local greenhouse effect from the released steam and the residual heat in the crater would have added more melting. Much of the freshwater could have ended in the nearby Labrador Sea, a primary site that pumps the Atlantic’s turnaround circulation. “It may potentially interfere with the circulation,” says Sophia Hines, a marine paleoclimatologist at Lamont-Doherty.
NASA and German aircraft used radar to see the contours of a battlefield under the ice of the Hiawatha glacier.
PHOTO: JOHN SONNTAG / NASA
Leery of the former controversy, Kjær will not support that scenario. “I’m not sitting in front of that wagon,” he says. But in draft paper, he acknowledges, the team obviously expressed a possible link between the Hiawatha influence and Younger Dryas.
SCIENCE STARTING with the ice. In the radar images, grit from remote volcanic eruptions breaks some of the boundaries between seasonal layers like bright reflections. The light layers can be matched with the same layer of gravel in cataloged, dated ice cores from other parts of Greenland. Using this technique, Kjar’s team found that most of the ice in Hiawatha are perfectly laid out for the last 11,700 years. But in the older, disturbed ice, the bright reflections disappear. Tracking the deep layers, the team matched the jumble with junk surface on Hiawatha’s edge dating back to 12,800 years ago. “It was quite self-consistent that the ice flow was severely disturbed at or before the younger Dryas,” said MacGregor.
Other evidence evidence also suggests that Hiawatha may be the younger Dryas effect. In 2013, Jacobsen examined an ice core from central Greenland, 1000 kilometers away. He expected to put the younger Dryas effect theory to rest by showing that 12,800 years ago tended levels of metals that the asteroid effect tends to spread does not spike. Instead, he found a top in the platinum, similar to those measured in samples from the crater. “It suggests a connection to Younger Dryas there,” says Jacobsen.
Broecker complements the coincidence. He had first been fascinated by the Firestone paper, but quickly joined the naysayer joints. Advocates of the younger Dryas effect put too much on it, he says: the fires, the eradication of megafauna, the abandonment of the Clovis sites. “They put a bad shine on it.” But the platinum top Jacobsen found, followed by the discovery of Hiawatha, has made him believe again. “It must be the same,” he says.
But no one can be sure of the time. The disturbed layers can not reflect more than normal tensions deep in the ice. “We know too well that older ice can be lost by cutting or melting in the base,” said Jeff Severinghaus, a paleoclimatologist at Scripp’s Institution of Oceanography in San Diego, California. Richard Alley, a glaciologist at Pennsylvania State University at University Park, believes the effect is much older than 100,000 years and that a subglacial lake can explain the odd textures near the bottom of the ice. “The flow of ice over growing and shrinking lakes that co-operate with coarse topography may have produced quite complex structures,” says Alley.
Kurt Kjær was searching for 2016 evidence that an effect in the sand was rinsed from under the Hiawatha glacier. He would find glassy pearls and shocked quartz quartz.
PHOTO: SVEND FUNDER
A new influence should also have left its trademark in the half-dozen deep ice cores bored elsewhere in Greenland, documenting the 100,000 years of today’s ice history. Yet none of the thin layers of raw materials that a Hiawatha size would have kicked up. “You should really see something,” says Severinghaus.
Brandon Johnson, a planet scientist at Brown University, is not so sure. After watching a draft study, Johnson, who modeled effects on odd mons like Europe and Enceladus, used his code to recreate an asteroid impact on a thick ice sheet. An impact digs a crater with a central peak like that seen on Hiawatha, he found, but the ice suppresses the spread of rocky debris. “Initial results are that it goes much less far,” said Johnson.
EVEN IF ASTEROID struck at the right moment, it could not have released all the disasters that were foretold by advocates of Younger Dryas. “It’s too small and too far to kill Pleistocene mammals in continental America,” says Melosh. And how a strike can spark flames in such a cold, barren region is hard to see. “I can not imagine how something like this impact on this site could have caused massive fires in North America,” says Marlon.
It may not even trigger Younger Dryas. The sediment cores of the sea show no signs of a rise of freshwater in the Labrador Sea from Greenland, says Lloyd Keigwin, a paleoclimatologist at Woods Hole Oceanographic Institution in Massachusetts. The best newest evidence, he adds, suggests a flood in the Arctic through Western Canada instead.
Bandade patterns in the mineral quake diagnose shock waves from an alien influence.
PICTURE: ADAM GARDE, GEUS
] An external trigger may in any case be unnecessary, Alley says. During the last Ice Age, the North Atlantic saw 25 other cooling games, probably due to disturbances in the Atlantic’s rotational circulation. None of these rods, called Dansgaard-Oeschger (D-O), were as difficult as Younger Dryas, but their frequency indicates that an internal bike played a role even in the younger Dryas. Broecker also agrees that the impact was not the main reason for the cooling. If the D-O events represent abrupt transitions between two common seas, he says: “You can say that the ocean approached instability and somehow struck this event.”
Yet, Hiawatha’s entire story will come down in his age. Even an exposed battlefield can be a challenge to date, which requires capturing the moment when the influence changes existing rocks – not the original age of the artery or its goal. Kjars team has tried. They fired lasers at the glassy balls to release argon to die, but the samples were too contaminated. The researchers inspect a blue crystal of mineral apatite for lines left by uranium decay, but it is a long shot. The team also found traces of coal in other samples, which can ever give a date, says Kjær. But the ultimate answer may require drilling through the ice to the crater floor, to cut that melt in the shock, restore its radioactive clock. With large accurate samples, researchers should be able to squeeze down Hiawatha’s age.
Given the remote location, a drill run to the hole in the world peak would be expensive. But an understanding of the latest climate story – and what a huge impact on the planet can be – is at stake. “Somebody has to go in there,” Keigwin says. “That’s all there.”