Tucked a kilometer below the surface of the Hiawatha Glacier in northwest Greenland, this impact crater has been challenging scientists since its discovery in 2015. Its 31 km diameter is enough to contain a city the size of Washington DC, probably the work of an asteroid one to two kilometers wide. But when did this monstrous collision occur? This is the puzzle that two independent teams from the University of Copenhagen in Denmark and the Natural History Museum in Stockholm in Sweden have solved.
Maps showing the location of the Hiawatha impact crater in northwest Greenland (left) and the shape of the Earth’s surface under the ice, showing the crater on the right. Credits: University of Copenhagen
Modern human influence?
Among the many speculations about the Hiawatha crater – the first to be discovered under the ice – is that it was formed only 13,000 years ago, when people had long settled the planet. The hypothesis shed light on the last ice age, which paleoclimatologists call the Dryas, a series of three periods of cooling that occurred between 16,500 and 11,700 years ago. Thus, the impact on the origin of Hiawatha Crater must have contributed to the last of these three periods, the Younger Dryas, which began 12,900 years ago and lasted 1,200 years. “Debris thrown into the atmosphere (water vapor, ash and dust) could affect the climate and melt a lot of ice. Thus, a sudden influx of cold water into the Nares Strait between Canada and Greenland could have occurred, which could have affected the sea currents of the entire region, causing the water and land to cool.explained in 2018 John Paden, a professor at the University of Kansas and co-author of a study reporting a surprising discovery in Scientific achievements.
View of the wall of the Hiawatha crater in Greenland. (Credit: Shfaqat Abbas Khan)
Difficult date
In reality, it turns out that the Hiawatha crater is much older: 58 million years old!
Tucked a kilometer below the surface of the Hiawatha Glacier in northwest Greenland, this impact crater has been challenging scientists since its discovery in 2015. Its 31 km diameter is enough to contain a city the size of Washington DC, probably the work of an asteroid one to two kilometers wide. But when did this monstrous collision occur? This is the puzzle that two independent teams from the University of Copenhagen in Denmark and the Natural History Museum in Stockholm in Sweden have solved.
Modern human influence?
Among the many speculations about the Hiawatha crater – the first to be discovered under the ice – is that it was formed only 13,000 years ago, when people had long settled the planet. The hypothesis shed light on the last ice age, which paleoclimatologists call the Dryas, a series of three periods of cooling that occurred between 16,500 and 11,700 years ago. Thus, the impact on the origin of Hiawatha Crater must have contributed to the last of these three periods, the Younger Dryas, which began 12,900 years ago and lasted 1,200 years. “Debris thrown into the atmosphere (water vapor, ash and dust) could affect the climate and melt a lot of ice. Thus, a sudden influx of cold water into the Nares Strait between Canada and Greenland could have occurred, which could have affected the sea currents of the entire region, causing the water and land to cool.explained in 2018 John Paden, a professor at the University of Kansas and co-author of a study reporting a surprising discovery in Scientific achievements.
Difficult date
In reality, it turns out that the Hiawatha crater is much older: 58 million years old! According to new dates, this time not based on the geomorphology of the crater, but thanks to the analysis of impact rocks. In his study, published Scientific achievementsTeams say they have recovered samples of molten sand and shattered zircon crystals washed away by meltwater from the glacier. “Dating the crater was particularly difficult to establish, so it’s very pleasing that the two labs, using different methods, came to the same conclusion. Thus, I’m confident that we have determined the true age of the crater, which is much older than many thought”, explains Michael Storey of the Natural History Museum of Denmark and co-author of this new study in a press release. On the one hand, the sand was analyzed by heating the grains with a laser until they released the argon used for dating. The Swedish team was responsible for rock analysis using uranium-lead dating of the mineral zircon. So for a consistent result: 58 million years. “Determining this new age of the crater surprised us all”said Gavin Kenny from the Swedish side of the study.
What are the disturbances of the Earth’s climate?
Thus, the collision occurred “only” 8 million years after the fall of another, better known asteroid and 10 times more; the one that led to the extinction of non-avian dinosaurs 66 million years ago, crashing at Chicxulub in Mexico’s Yucatán Peninsula. The latter, estimated to be between 10 and 15 km in size, left a crater about 180 km in diameter, much larger than Hiawatha’s 31 km crater. One way or another, 58 million years ago, the Earth “recovered” from the catastrophe and entered a period of warming. The hard-hit Arctic was then covered by temperate rainforest with standards hovering around 20°C and home to rich wildlife. Scientists are now left to study how Hiawatha’s impact may or may not have affected local and global climate. Thus, very far from the cooling of the Younger Dryas, it could have been involved in triggering the great warming (+6°C in 20,000 years) that marked the transition from the Paleocene to the Eocene.
Above is a NASA video released in 2018 before the crater was dated.