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Greenland asteroid struck world recovering from dinosaur extinction
An asteroid strike in what is now Greenland has been dated to 58 million years ago - just eight million years after the one that caused the extinction of the dinosaurs.
While the impacts of this more recent asteroid are uncertain, it could have caused the world to warm significantly in the aftermath of the fifth mass extinction.
A suspect has been ruled out of a historical whodunnit of what caused the world to suddenly become 10⁰C colder 13,000 years ago.
A team of researchers has found it couldn't have been an asteroid impact in Greenland. Since its discovery in 2015, the Hiawatha crater had been considered a possible explanation for why this period of Earth's history, known as the Younger Dryas, was so cold.
However, the scientists investigating the crater, which is large enough to contain the UK city of Birmingham, found that it is much older than first thought, having formed over 58 million years ago.
Co-author Professor Michael Storey says, '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.'
Its recalculated age makes it possible that the asteroid influenced the Earth's ecosystems when they were still recovering from the impact of the even larger asteroid that hit eight million years before.
The findings of the study, conducted by an international team of scientists, were published in Science Advances.
While many have been eroded away, other meteorite craters remain very prominent. Image © Kit Leong/Shutterstock
What are asteroids?
Asteroids are large rocky bodies that are orbiting the Sun, made up of leftovers from the formation of the Solar System. Most known asteroids are found inside the asteroid belt, located between Mars and Jupiter.
They can form in a variety of ways, such as accreting from small particles floating in space or being the debris left over from collisions. These collisions can sometimes knock asteroids out of the asteroid belt and put them on their own orbital path.
When these enter a planet's atmosphere, they become known as a meteor. If they survive the trip through the atmosphere, they are then described as a meteorite. Any planet can be struck by asteroids, and Earth is no exception.
The largest crater left behind by a meteorite is the Vredfort crater in South Africa. Measuring up to 300 kilometres across when it was first formed, it is believed to be the result of a 10-kilometre-wide meteorite hitting Earth two billion years ago.
Other large impact craters can be found in Canada's Sudbury basin, Australia's Acraman crater and Russia's Kara crater. However, perhaps the most famous is the Chicxulub crater in Mexico, which is believed to be the remnant of the asteroid strike which wiped out the dinosaurs.
Following the shockwave and massive energy release, surviving organisms faced large amounts of debris in the atmosphere which blocked out a significant amount of sunlight. This would have significantly cooled the planet and helped drive many surviving species extinct.
As a result, asteroids have long been considered a potential cause of the sharp decline in temperature in the Younger Dryas. The discovery of the Hiawatha crater, which sits within the biggest 10% of impact strikes on Earth, seemed to be a likely candidate.
However, sampling of the site has now shown that Hiawatha was not to blame, at least not for the Younger Dryas.
Rock and sand samples were taken from near the Hiawatha glacier which is eroding the crater underneath. Image © Pierre Beck
What did the Hiawatha asteroid do?
The crater lies deep under the Greenland ice sheet making it inaccessible. Scientists instead took sand and melt rock samples formed by the erosion of the crater by a glacier to chemically assess its age.
Two separate methods of dating, one using uranium and lead and the other using argon, were used. They both suggest that the crater formed around 58 million years ago, substantially pushing its age back.
This means that when it hit what is now Greenland its ice sheet didn't exist, and wouldn't for at least another 55 million years. Instead, the island would have been covered in large coniferous forests, with average temperatures of around 20⁰C.
On striking this area, the Hiawatha asteroid created a crater 31 kilometres wide and a kilometre deep. It would have been devastating to the area it struck, releasing the equivalent energy of around seven million atomic bombs.
Whether it had any affect on the wider world, however, remains uncertain. The date of the meteor strike coincides with the Paleocene Carbon Isotope Maximum, after which the world began to warm up as carbon was released from reservoirs such as bogs and the ocean into the atmosphere.
However, no layer of debris from the impact has yet been discovered which might confirm this. This is something the researchers hope to investigate going forward.
Lead author Dr Gavin Kenny says, 'Determining the new age of the crater surprised us all. In the future, it will help us investigate the impact's possible effect on climate during an important epoch of Earth's history.'
