A field photo taken at Stoer showing the laminar beds of sandstone in the bottom of the picture. In the middle is the impact deposit (12m thick at this location) that contains "rafts" of deformed pink sandstone.

Site of biggest ever meteorite collision in the UK discovered

The quest to discover the exact location of where the biggest meteorite hit the British Isles -around 1.2 billion years ago – has taken a new twist.

Scientists from the universities of Oxford and Exeter believe they have identified the meteor’s impact site in north-west Scotland.

The first suggestion of an ancient, meteorite crater was first mooted in 2008, when scientists found evidence on the Highlands coast for the rocky debris that would have been produced by a giant impact.

Although the thickness and extent of debris deposit suggested an impact crater – made by a meteorite estimated at 1km wide –its precise location remained a mystery. 

Now a team led by Dr Ken Amor from the Department of Earth Sciences at Oxford University and including Professor Stephen Hesselbo from the University of Exeter, Camborne School of Mines, identifies the crater location as being 15-20 km west of a remote part of the Scottish coastline.

The research, published in Journal of the Geological Society, suggests it is buried beneath both water and younger rocks in the Minch Basin.

Professor Hesselbo, a Geology expert at the Camborne School on Mines, based at the University of Exeter’s Penryn Campus said: “for ten years since discovery of the debris from the impact, there has been a lot of speculation about the location of the impact crater, and now we have some solid evidence for its location.”

Using a combination of field observations, the distribution of broken rock fragments known as basement clasts and the alignment of magnetic particles, the team was able to gauge the direction the meteorite material took at several locations, and plotted the likely source of the crater.

Lead author, Dr Ken Amor said: ‘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.

It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.

“It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area.”

1.2 billion years ago most of life on Earth was still in the oceans and there were no plants on the land. At that time Scotland would have been quite close to the equator and in a semi-arid environment. The landscape would have looked a bit like Mars when it had water at the surface. 

Earth and other planets may have suffered a higher rate of meteorite impacts in the distant past, as they collided with debris left over from the formation of the early solar system.

However, there is a possibility that a similar event will happen in the future given the number of asteroid and comet fragments floating around in the solar system. Much smaller impacts, where the meteorite is only a few metres across are thought to be relatively common perhaps occurring about once every 25 years on average. 

It is thought that collisions with an object about 1 km (as in this instance) across occur between once every 100,000 years to once every one million years - but estimates vary. One of the reasons for this is that our terrestrial record of large impacts is poorly known because craters are obliterated by erosion, burial and plate tectonics.

The next step, according to the research team, should be a detailed geophysical survey in the target area of the Minch Basin.

Date: 10 June 2019

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