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The huge Hiawatha impact crater, 31 km wide, lies buried a kilometer deep under the Greenland ice. It is one of the largest of the approximately 200 known on Earth. For years, it has been suspected that it might have been created by an asteroid or a comet that hit 13,000 years ago, when humanity had already been on the planet for hundreds of thousands of years. However, Danish and Swedish researchers have re-dated the crater and their results determine that not a single human being might feel the effects of the cosmic crash. Simply because it happened long before we showed up. As explained in
‘Science Advances’, the Greek one was left behind by an asteroid that fell 58 million years ago, not long following the one that wiped out the dinosaurs did.
Researchers at the GLOBE Institute at the University of Copenhagen discovered the hiawatha crater, in northwestern Greenland, in 2015. Since then, uncertainty regarding the age of the crater has been the subject of considerable speculation. If it was only 13,000 years old, might it have ushered in a mini ice age that lasted more than 1,000 years?
New analyzes performed on grains of sand and rocks from the crater show that the answer is no. The Hiawatha impact crater is much older. Its age, 58 million years, indicates that it fell ‘only’ regarding eight million years following a meteorite of regarding 10 km in length hit what is now the province of Yucatan, in Mexico, leaving a crater, that of Chicxulub, much larger -regarding 200 meters in diameter- and ending much of the life that existed then, including the dinosaurs.
“Dating the crater has been a particularly difficult nut to crack, so it is very satisfying that two laboratories in Denmark and Sweden, using different dating methods, have come to the same conclusion. As such, I am convinced that we have determined the true age of the crater, which is much older than many people thought,” says Michael Storey of the Natural History Museum of Denmark.
“It is fantastic to know now his age. We have been working hard to find a way to date the crater since we discovered it seven years ago. Since then, we have made several field trips to the area to collect samples,” says Nicolaj Krog Larsen of the GLOBE Institute.
Laser beams and grains of sand
No kilometer-thick ice sheet covered northwestern Greenland when asteroid Hiawatha slammed into Earth’s surface, releasing several million times more energy than an atomic bomb. At the time, the Arctic was covered in temperate rainforest and wildlife abounded, and temperatures of 20 degrees Celsius were the norm.
The asteroid crashed into Earth, leaving a crater thirty-one kilometers wide and one kilometer deep, large enough to easily contain the entire city of Barcelona. Today, the crater lies below the Hiawatha Glacier in northwestern Greenland. Rivers flowing from the glacier supplied researchers with sand and rocks that were superheated by the impact 58 million years ago.
The sand was analyzed at the Natural History Museum of Denmark by heating the grains with a laser until they released argon gas, while the rock samples were analyzed at the Swedish Museum of Natural History using uranium-lead dating of the mineral zircon.
“The determination of the new age of the crater surprised us all. In the future, it will help us investigate the possible effect of the impact on climate during an important time in Earth’s history,” says Gavin Kenny of the Swedish Museum of Natural History.
Although the Hiawatha impact crater is much smaller than the Chicxulub impact crater, it would have devastated the region and might even have had broader consequences for climate and plant and animal life. When the impact occurred, the Earth had recovered from the catastrophic effects of the Chicxulub impact and was entering a long-term warming trend that would last regarding 5 million years.
Clear evidence that the Hiawatha impact altered global climate is still lacking. However, the dating of the crater allows the research team to start testing various hypotheses to better understand what the consequences of the impact were on the climate and, therefore, on life on Earth.
