The impact crater of the largest meteorite ever to strike the UK has been discovered 25 miles off the coast of northwest Scotland.
The one kilometre wide, three billion tonne rock smashed down in the Minch basin, between what is now the isles of Lewis and Harris in the Outer Hebrides and the town of Ullapool.
British researchers said a witness to the strike 1.2bn years ago would have had "quite a spectacle" as the meteor travelling at 40,000mph struck Earth with a force 940 million times greater than the Hiroshima bomb.
Despite it leaving a 40km-wide crater, the Aberdeen and Oxford team said it was pure chance that any trace had been preserved over the millennia.
"The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery,” said Dr Ken Amor of Oxford University.
“It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.”
Scientists first discovered evidence of the ancient strike 11 years ago near UIlapool.
Now they have spotted the heart of the impact zone in the Minch, between 15 and 20km west of a remote part of the beach. It is buried beneath both the water and younger rocks.
They will now begin leading surveys of the site to learn more about the impact and the early days of the strike.
“It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area,” Dr Amor added.
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| A field photo taken at Stoer. The way the rocks are laid out provides clues on the impact deposit left by the asteroid |
At the time, most life was still in the oceans and there were no plants on the land. Scotland would have been quite close to the equator and in a semi-arid environment.
The “ejecta blanket” thrown out by the strike would have scattered this cloud 50km away, the researchers said, in findings published in the Journal of the Geological Society.
In the rocks, there were also elevated levels of the element iridium, which is characteristic of extra-terrestrial material. There were also microscopic parallel fractures that also imply a meteorite strike.
It has led them to re-evaluate the formation of certain unusual rocky outcrops that were previously attributed to volcanic activity.
Mass Ejection
This artist's illustration depicts a coronal mass ejection, or CME, which involves a large-scale expulsion of material, and has frequently been observed on our Sun. A new study using the Chandra X-ray Observatory detected a CME from a star other than our own for the first time, providing a novel insight into these powerful phenomena.
Experts estimate the Earth experiences a collision with an object this size between once every 100,000 years to once every one million years.
Our terrestrial record of large impacts is poorly known because craters are often obliterated by erosion, burial and plate tectonics.
Much smaller impacts, where the meteorite is only a few metres across, are thought to be relatively common – perhaps happening about once every 25 years on average.
The largest crater made by a meteor or comet was discovered in the Australian outback four years ago.
It has a 400km diameter and is believed to have occurred more than 300 million years ago.
The 150km-wide Chicxulub buried beneath Mexico’s Yucatan Peninsula is the most famous of them all. It was created by an asteroid 66 million years ago and is believed to have been responsible for wiping out the dinosaurs.
