Scientists have long been perplexed by the age of a 31-kilometer (19-mile) broad meteorite crater located beneath a kilometer of Greenland ice.
Despite glacier ice being extremely powerful in erosion, the Hiawatha crater was remarkably well preserved. Its government fuelled speculation that the meteorite struck as recently as 13,000 years ago.
Michael Storey, head of geology at the Natural History Museum of Denmark said, "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."
The crater, which is one of the biggest in the world, has now been scientifically dated, and it is much, much older. In reality, it blasted into the Earth roughly 58 million years ago, only a few million years after dinosaurs were extinct.
It is larger than 90 percent of the roughly 200 previously known impact craters on Earth and might swallow Washington, DC. In Greenland, the researchers gathered sand and rock samples to figure out when the meteor struck.
It's unclear if the meteor that hit Greenland altered global climate in the same way as the 200-kilometer-wide asteroid that produced the Chicxulub crater in Mexico 8 million years ago did. The Greenland meteorite, on the other hand, would have wreaked havoc on nearby plant and animal life.
Researchers used sand and boulders gathered from the glacier's waterways to date it. As a result of the meteor impact, the samples would have been warmed. They were dated by detecting the natural decay of long-lived natural radioisotopes present in the rock using methods that detect natural radioisotope decay.
Uranium-lead dating was used to determine the age of zircon crystals found in the rock. As zircon crystallizes, the uranium isotopes begin to decay, changing into lead isotopes at a regular and predictable pace. The method yielded a date of around 58 million years ago.
The release of argon gas, which is created by the decay of the uncommon but naturally occurring radioactive isotope of potassium known as K-40, was monitored after the grains of sand were burned with a laser.
"The half-life of K-40 is exceptionally long (1,250 million years) which makes it ideal for dating deep-time geological events like the age of the Hiawatha asteroid," Storey said.
Nicolaj Krog Larsen, who discovered the crater first, said, "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."