Danish and Swedish researchers have dated the enormous Hiawatha impact crater, a 31 kilometer-wide meteorite crater buried under the Hiawatha Glacier in northwestern Greenland. The dating ends speculation that the meteorite has anything to do with the Younger Dryas climate shift or the extinction of the megafauna about 10,000 years ago.
Ever since 2015, when researchers at the University of Copenhagen's GLOBE Institute discovered the Hiawatha crater, uncertainty about the crater's age has been the subject of considerable speculation. Could the asteroid have slammed into Earth as recently as 13,000 years ago, when humans had long populated the planet? Could its impact have catalyzed a nearly 1,000-year period of global cooling known as the Younger Dryas? Could this climatic shift explain the extinction of the iconic megafauna, including mammoths?
Covered by more than 1,000 meters of ice, it is not possible to access the crater and directly determine its age. Based on ice thickness and rates of ice erosion, experts suggested that the crater was at least 12,000 to 100,000 years old.
According to a news release by the University of Copenhagen, an analyses performed on grains of sand and rocks washed by meltwater from the crater site to the borders of the glacier, the Hiawatha impact crater is far older. In fact, a new study published in the journal Science Advances today reports its age to be 58 million years old.
"Dating the crater has been a particularly tough nut to crack, so it's very satisfying that two laboratories in Denmark and Sweden, using different dating methods arrived at the same conclusion. As such, I'm convinced that we've determined the crater's actual age, which is much older than many people once thought," says Michael Storey, co-author of the study.
As one of those who helped discover the Hiawatha impact crater in 2015, Professor Nicolaj Krog Larsen of the GLOBE Institute at the University of Copenhagen is pleased that the crater's exact age is now confirmed.
"It is fantastic to now know its age. We've been working hard to find a way to date the crater since we discovered it seven years ago. Since then, we have been on several field trips to the area to collect samples associated with the Hiawatha impact," says Professor Larsen.
No kilometer-thick ice sheet draped Northwest Greenland when the Hiawatha asteroid rammed into Earth surface releasing several million times more energy than an atomic bomb. At the time, the Arctic was covered with a temperate rainforest and wildlife abounded—and temperatures of 20 degrees Celsius were the norm. Eight million years earlier, an even larger asteroid struck present-day Mexico, causing the extinction of Earth's dinosaurs.
The asteroid smashed into Earth, leaving a thirty-one-kilometer-wide and one-kilometer-deep crater. The crater is big enough to contain the entire city of Washington D.C. During the impact high-pressure and high-temperature minerals, like zircon, formed in the rocks surrounding the impact site. The crystalline structure of zircon contains radioactive elements. As they decay to stable lead, the remaining levels of radioactive elements can be used to pinpoint the age of the crystal. The scientists extracted the zircon crystals from sand grains and pebbles washed by meltwater from beneath the glacier to its accessible borders.
The sand was analyzed at the Natural History Museum of Denmark by heating the grains with a laser until they released argon gas, whereas the rock samples were analyzed at the Swedish Museum of Natural History using uranium-lead dating of the mineral zircon.
