[meteorite-list] Diamonds tell tale of comet ....

From: Mike Groetz <mpg444_at_meteoritecentral.com>
Date: Mon, 21 May 2007 09:55:14 -0700 (PDT)
Message-ID: <228215.98225.qm_at_web32901.mail.mud.yahoo.com>

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http://www.guardian.co.uk/science/story/0,,2083785,00.html

Diamonds tell tale of comet that killed off the
cavemen
Fireballs set half the planet ablaze, wiping out the
mammoth and America's Stone Age hunters

Robin McKie, science editor
Sunday May 20, 2007

Observer

Scientists will outline dramatic evidence this week
that suggests a comet exploded over the Earth nearly
13,000 years ago, creating a hail of fireballs that
set fire to most of the northern hemisphere.
Primitive Stone Age cultures were destroyed and
populations of mammoths and other large land animals,
such as the mastodon, were wiped out. The blast also
caused a major bout of climatic cooling that lasted
1,000 years and seriously disrupted the development of
the early human civilisations that were emerging in
Europe and Asia.

'This comet set off a shock wave that changed Earth
profoundly,' said Arizona geophysicist Allen West. 'It
was about 2km-3km in diameter and broke up just before
impact, setting off a series of explosions, each the
equivalent of an atomic bomb blast. The result would
have been hell on Earth. Most of the northern
hemisphere would have been left on fire.'

The theory is to be outlined at the American
Geophysical Union meeting in Acapulco, Mexico. A group
of US scientists that include West will report that
they have found a layer of microscopic diamonds at 26
different sites in Europe, Canada and America. These
are the remains of a giant carbon-rich comet that
crashed in pieces on our planet 12,900 years ago, they
say. The huge pressures and heat triggered by the
fragments crashing to Earth turned the comet's carbon
into diamond dust. 'The shock waves and the heat would
have been tremendous,' said West. 'It would have set
fire to animals' fur and to the clothing worn by men
and women. The searing heat would have also set fire
to the grasslands of the northern hemisphere. Great
grazing animals like the mammoth that had survived the
original blast would later have died in their
thousands from starvation. Only animals, including
humans, that had a wide range of food would have
survived the aftermath.'

The scientists point out that archaeological evidence
shows that early Stone Age cultures clearly suffered
serious setbacks at this time. In particular, American
Stone Age hunters, descendants of the hunter-gatherers
who had migrated to the continent from Asia, vanished
around this time.

These people were some of the fiercest hunters on
Earth, men and women who made magnificent stone
spearheads which they used to hunt animals including
the mammoth. Their disappearance at this time has been
a cause of intense debate, with climate change being
put forward as a key explanation. Now there is a new
idea: the first Americans were killed by a comet.

It was not just America that bore the brunt of the
comet crash. At this time, the Earth was emerging from
the last Ice Age. The climate was slowly warming,
though extensive ice fields still covered higher
latitudes. The disintegrating comet would have plunged
into these ice sheets, causing widespread melting.
These waters would have poured into the Atlantic,
disrupting its currents, including the Gulf stream.
The long-term effect was a 1,000-year cold spell that
hit Europe and Asia.

The comet theory, backed by observational evidence
collected by the team, has excited considerable
attention from other researchers, following
publication of an outline report of the work in Nature

'The magnitude of this discovery is so important,'
team member James Kennett, of the University of
California, Santa Barbara, told the journal. 'It
explains three of the highest-debated controversies of
recent decades.'

These are the sudden disappearance of the first Stone
Age people of America, the disappearance of mammoths
throughout much of Europe and America and the sudden
cooling of the planet, an event known as the
Younger-Dryas period. Various theories have been put
forward to explain these occurrences, but now
scientists believe they have found a common cause in a
comet crash. However, the idea is still controversial
and the theory is bedevilled by problems in obtaining
accurate dates for the different events.

'We still have a long way to go,' admitted West. 'But
we have a great deal of evidence, from many sites, so
this is quite a powerful case that we are making.'




       
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Received on Mon 21 May 2007 12:55:14 PM PDT