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article imageAsteroid impact crater found off the coast of Scotland

By Karen Graham     Jun 10, 2019 in Science
The location of an ancient impact crater made by the biggest asteroid ever to hit Britain has been traced to a spot under the sea between mainland Scotland and the Outer Hebrides.
Researchers at Oxford and Aberdeen universities think the time is right for a full geophysical survey of The Minch, to see if the Scottish strait is hiding an ancient meteorite crater, reports The BBC.
The scientists believe the crater was formed about 1.2 billion years ago when the continents were arranged differently from their positions today and the only life existing was almost exclusively found in the oceans.
As evidence, the researchers cite a group of reddish-colored rocks discovered in 2008 on the Highlands coast along the eastern side of The Minch known as the Stac Fada deposit. Oxford researcher Ken Amor was one of the original scientists on the 2008 expedition that found the strange rock formations.
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Writing in the Journal of the Geological Society, the researchers say they have finally pinpointed where the asteroid came down. Tests on rocks found near Ullapool confirmed them to be ejecta from the impact - the material hurled outwards when a 1-2 kilometer (one-mile) wide object slammed into what is now the Minch, a strait that separates the mainland and the northern Inner Hebrides from Lewis and Harris, six miles west of the village of Lochinver.
The discovery in the village of Stoer
Dr. Amor explains that he was helping undergraduate students on a geology field trip in the Scottish Highlands in 2008, and on the final day of the field trip, the scientists stopped in Stoer, a small village, to inspect an unusual rock formation known as the Stac Fada member (SFM).
Scientists had long speculated that the distinctive red limestone in the Stac Fada had come from volcanic activity. But Amor was drawn to the strange "green blobs" in the rock. They very much resembled features of an impact crater in the town of Nördlingen near the Danube in western Bavaria.
Dr. Amor took rock samples back to Oxford for further examination and testing. The rock contained high levels of platinum and palladium, and what geologists term shocked quartz - a type of mineral that has at some point been subjected to enormous pressures.
A close-up picture of spherules known as accretionary lapilli that form in the impact plume cloud  a...
A close-up picture of spherules known as accretionary lapilli that form in the impact plume cloud, and found in the deposit.
Dr. Ken Amor
The tests have now given researchers from Oxford and the Camborne School of Mines information that allows them to be more precise in determining where the ejecta came from.
"If you imagine debris flowing out in a big cloud across the landscape, hugging the ground, eventually that material slows down and comes to rest. But it's the stuff out in front that stops first while the stuff behind is still pushing forward and it overlaps what's in front," explained Dr. Amor.
"That's what we see and it gives us a strong directional indicator that we can trace backward. Also, we've examined the orientation of magnetic particles within the fabric of the rock at several locations, and this too allows us to triangulate back to an origin," the Oxford researcher told BBC News.
The magnetic lines converge out in The Minch.
What is in the strait?
Imagine, if you will, an asteroid a mile-wide, hurtling toward the Earth at 38,000 mph - thumping into the ground, creating a 12-mile-wide crater. It would have been dramatic, sending a mushroom cloud and fireball high into the sky,
Illustration of an en:impact event.
Illustration of an en:impact event.
Fredrik at English Wikipedia.
However, it was minor compared with the spectacular strike in Mexico’s Yucatán peninsula 66 million years ago, when an asteroid estimated at six to 50 miles wide put an end to the reign of the dinosaurs.
What is left of the crater in Scotland lies 650 feet under the waters of the strait, and researchers are hopeful that the crater hasn't eroded away.
The researchers plan on using several techniques to pinpoint the crate, including a seismic reflection technique used by oil prospecting companies to confirm the crater's location. They are also investigating gravity data which indicates an anomaly in the strait.
"What we really need is a new high-resolution geophysical survey - a 3D seismic survey," said Dr. Amor. "Unfortunately, being offshore that would cost a lot of money. I shall be putting in a grant proposal to do some seismic work. That would be the first step and would greatly assist the definition of an impact structure."
More about Scotland, Stac Fada deposit, Asteroid, impact crater, 12 billion years ago
 
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