A massive impact crater beneath Greenland’s ice sheet was produced by an asteroid or comet slamming into Earth 58 million years ago, according to a new study in the journal Science Advances.
It had been previously suggested that the space rock responsible for the crater may have struck while humans roamed the Earth, yet these new findings indicate that the event actually occurred just a few million years after the age of dinosaurs.
Called the Hiawatha crater, the 31-kilometer (19.3-mile) wide impact sits beneath a kilometer of ice in northwest Greenland. it was first detected in 2015 during a study of the ice sheet’s thickness.
Charcoal particles collected from the glacial meltwater were initially assessed to have been derived from plant species that existed during the Pleistocene, which ended around 11,700 years ago.
Based on these findings, researchers speculated that the Hiawatha crater may have formed around 13,000 years ago, potentially triggering a period of global cooling called the Younger Dryas. This scenario fits perfectly with the so-called Younger Dryas impact hypothesis, which posits that fragments of a colossal, disintegrating space rock struck the Earth at multiple locations roughly 12,800 years ago, prompting a return to glacial conditions that lasted for about a millennium.
To determine the crater's true age, the authors of this latest study examined sediments in the meltwater that displayed clear signs of having been affected by an asteroid impact. This included grains of sand from partially melted rocks and small stones containing crystals made of “shocked” zircon.
They then dated the sand by heating grains with a laser until they released argon. By analyzing the different argon isotopes present in their sample, they determined that the rocks from which the sand was created were impacted 58 million years ago.
By then measuring the rate of decay of uranium within the shocked zircon crystals, it was confirmed that these too were produced 58 million years ago, thus providing pretty conclusive evidence for the age of the Hiawatha crater.
"Dating the crater has been a particularly tough nut to crack,” explained study author Michael Storey in a statement. “I'm convinced that we've determined the crater's actual age, which is much older than many people once thought," he added.
These findings indicate that the Hiawatha asteroid did not strike our planet during the age of humans or contribute to the Younger Dryas. Furthermore, the timing of the impact is out of sync with a major warming event around 56 million years ago, raising questions as to what influence the collision may have had on the global climate.
The researchers, therefore, call for more studies into the nature of the ejecta produced by the event, which they say might “enable direct integration of the impact event with sedimentary climate proxies.”