[meteorite-list] Another new old crater

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 26 Mar 2008 11:20:08 -0500
Message-ID: <1qtku3tb542rs6la22jq8gc6e6mkiu31ob_at_4ax.com>

http://news.bbc.co.uk/2/hi/science/nature/7314329.stm

'Biggest UK space impact found'
By Paul Rincon
Science reporter, BBC News

Evidence of the biggest meteorite ever to hit the British Isles has been found
by a team of scientists.
Researchers from the universities of Oxford and Aberdeen think a large object
hit north-west Scotland about 1.2 billion years ago.

The space rock struck the ground near the present-day town of Ullapool, they
report in Geology journal.

The scientists found what they believe to be debris which was flung out when the
impact crater was formed.

"If there had been human observers in Scotland 1.2 billion years ago, they would
have seen quite a show," said co-author Ken Amor, from the University of Oxford.

"The massive impact would have melted rocks and thrown up an enormous cloud of
vapour that scattered material over a large part of the region around Ullapool.
The crater was rapidly buried by sandstone which helped to preserve the
evidence."

The crater is suspected to lie under the Minch, the waterway that separates
Lewis in the Outer Hebrides from the north-west Highlands of Scotland.

Unusual rock formations in the area were previously thought to have been formed
by volcanic activity.

'Spectacular' strike

But Ken Amor and his colleagues found "ejecta blanket" evidence buried in rocks
from the area. This represents debris thrown out when the huge object slammed
into the ground.

Ejected material from the meteorite strike is scattered over an area about 50km
across.

In the rocks, the researchers found elevated levels of the element iridium,
which is characteristic of extra-terrestrial material. They also found
microscopic parallel fractures that also imply a meteorite strike.

Co-author John Parnell, a geologist at the University of Aberdeen, said:
"Building up the evidence has been painstaking, but has resulted in proof of the
largest meteorite strike known in the British Isles."

Mr Amor said this was the "most spectacular evidence for a meteorite impact
within the British Isles found to date".

He added: "What we have discovered about this meteorite strike could help us to
understand the ancient impacts that shaped the surface of other planets, such as
Mars."

The proposed volcanic origin for the rock formations had previously been a
puzzle, as there are no volcanic vents or other volcanic sediments nearby.

The UK's only other known space impact location is Silverpit in the North Sea.
Scientists have found evidence on the sea floor for a cataclysmic asteroid or
comet strike that occurred some 60-65 million years ago. The impact structure is
about 130km (80 miles) east of the Yorkshire coast.

Some researchers, though, have questioned its space origins.
Received on Wed 26 Mar 2008 12:20:08 PM PDT