Impact 'showered debris over Britain'

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Friday, 15 November, 2002, 13:01 GMT
Impact 'showered debris over Britain'

   



Map, bbc
The world looked very different 214 million years ago
   
By Helen Briggs
BBC News Online science reporter
Evidence has emerged of how Britain's history was shaped by an asteroid collision 214 million years ago.

Rock blasted out of the ground by an asteroid hitting the Earth has been found for the first time in the southwest of England.


The skies would have gone dark; then it would have rained hot dust and rocks

Simon Kelley, Open University
Canada still bears the scars of the explosion, which splattered hot rock and dust across the British Isles.

The space rock hit what is now Manicouagan, Quebec, opening up a 100-kilometre-wide (62-mile-wide) crater that can be seen by astronauts from space.

The Atlantic Ocean had not appeared at the time, so the two land masses (Europe and North America) were much closer than they are today.

The rock was found near Bristol by geologists at the University of Aberdeen.

Dr Gordon Walkden said: "We have found evidence of a massive shockwave carrying molten rock and dust that has left a thin layer of glass beads and shattered mineral grains across the ancient British land surface."

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Nuclear bomb

The material has the distinctive hallmark of an asteroid slamming into the planet.

The space body, about five km (three miles) wide, generated a shockwave 40 million times larger than the Hiroshima blast.




University of Aberdeen
The impact material was found among sediments of the late Triassic Period
Molten rock and debris were hurled high into the Earth's atmosphere, some of it falling on to Britain.

The landscape 214 million years ago was very different to the rolling green fields of today.

It was largely arid desert, sparsely populated by ferns, reptiles, lizards, and small mammals.

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 "Anything standing would have been flattened by the blast," said Dr Walkden, who discovered the rock in the 1980s.

He knew at once there was something unusual about the sample, which he describes as tiny green balls embedded in pinky-coloured rock, but its ancient origins have only just come to light.

"It was very clearly something strange that I wasn't able to identify at the time," the senior geology lecturer told BBC News Online. "It sat in a drawer for a long time."

It was to be 20 years before he realised its scientific value, when he saw similar deposits from a crater in Mexico, where the asteroid blamed for killing off the dinosaurs landed.

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Dark skies

According to Dr Simon Kelley, of the Open University in Milton Keynes, who dated the Bristol sample, it is the first recorded example of such an impact deposit in Britain.


The Manicouagan crater (Nasa)
The Canadian crater is visible from space
"If you had been in Britain at the time, the Sun would have been blotted out by the dust and gases from the impact," he told BBC News Online.

"First you would have seen a big flash over the horizon. Then the skies would have gone dark; then it would have rained hot dust and rocks. The effects would have lasted for years."

The shock wave from the asteroid would have carried molten rock and dust thousands of kilometres.

Scientists are now searching for other remnants of the blast to study what happened to biodiversity on Earth.

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Public display

The Canadian impact does not seem to have had as devastating an effect as the impactor that signalled the downfall of the dinosaurs.

University of Aberdeen
The rock was found at an outcrop near Bristol
This is thought to be because it hit normal rock, rather than salt deposits capable of releasing poisonous gas.

"It may well be that we might get devastating meteorite impacts in the future but it is unlikely that there will be a repeat of the impact that saw the end of the dinosaurs," said Dr Kelley.

A piece of the material discovered by Dr Walkden will be on display at the Darwin Centre at the Natural History Museum, London, on 15 November.

Specimens will also be on display at the National Space Centre in Leicester, the National Museum of Scotland, Edinburgh, and at the University of Aberdeen.

The research is published in the journal Science.

http://news.bbc.co.uk/2/hi/science/nature/2472903.stm