Enlarge image
Hidden Giant Crater: View of Hiawatha Glacier in Greenland
Photo: NASA
A huge crater in northwest Greenland, buried by a thick layer of ice and first discovered in 2015, is much older than first thought.
It was formed by a meteorite impact 58 million years ago.
The first estimates that the crater was 13,000 years old were off by a factor of 4460.
Researchers said Wednesday they used two different dating methods to examine sand and rock left by the impact to find out when the crater, about 31 kilometers wide, was formed.
They found that the meteorite, about 1.5 to 2 kilometers in diameter, struck Greenland about eight million years after the asteroid impact on Mexico's Yucatan Peninsula that wiped out the dinosaurs.
The crater is one of the 25 largest known impact craters on earth.
It lies under the Hiawatha Glacier with a layer of ice about a kilometer thick.
It was only discovered with the help of radar devices that can measure the ice from the air.
"The impact may have devastated the region," said geologist Gavin Kenny of the Natural History Museum in Stockholm, lead author of the study, published in the journal Science Advances.
The meteorite released millions of times more energy than an atomic bomb, and the crater could have swallowed up a modern city.
"The blast from the impact must have felled most of the trees," Kenny said.
Even hundreds of kilometers away, the heat wave would have set fire to the forests.
At the time of the impact, in the Paleocene, Greenland was not an icy landscape like it is today, but covered by temperate rain forest and inhabited by mammals, which became the dominant land animals on Earth after the dinosaurs went extinct.
The impact may also have triggered earthquakes in the region, Kenny said.
At the same time, it rained ash from the forest fires, as well as dust and molten rock that was violently thrown into the atmosphere.
A thick layer of rubble had settled on the ground.
No trigger of the Ice Age
As devastating as this event was, it fell far short of the devastation caused by the estimated 12-kilometre-diameter asteroid that slammed into the Yucatan 66 million years ago.
This wiped out three quarters of the species on earth and caused a global climate catastrophe.
"Whether the impact had a lasting effect on the world's climate is currently unclear, but I think it's unlikely," said geologist Michael Storey of the Copenhagen Geological Museum, a co-author of the study.
Some researchers previously assumed that the impact did not hit Greenland until after the ice sheet formed there 2.6 million years ago – maybe even around 13,000 years ago.
This could have been a reason for the ice age that began afterwards.
The researchers used dating methods based on radioactive decay.
Because the ice-covered crater is inaccessible, they sampled sand derived from rocks heated by the impact, as well as minerals called zircons contained in pebbles.
All of this was recovered from a river that washes material from the crater out of the glacier.
Both methods gave the same age of the material.
Geologist Kenny also had a reassuring message: “Impacts of this magnitude only happen every few million years.
So we don't have to worry too much about something like this happening again anytime soon."
ak/Reuters
