[meteorite-list] Astronomers Suggest Comet To Blame for 6th-Century 'Nuclear Winter'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:20 2004
Message-ID: <200402031639.IAA19331_at_zagami.jpl.nasa.gov>

Contact: Dr Derek Ward-Thompson
derek.ward-thompson_at_astro.cf.ac.uk
029-2087-5314
Cardiff University
February 3, 2004

Astronomers unravel a mystery of the Dark Ages

Undergraduates' work blames comet for 6th-century "nuclear winter"

Scientists at Cardiff University, UK, believe they have discovered the cause
of crop failures and summer frosts some 1,500 years ago - a comet colliding
with Earth.

The team has been studying evidence from tree rings, which suggests that the
Earth underwent a series of very cold summers around 536-540 AD, indicating
an effect rather like a nuclear winter.

The scientists in the School of Physics and Astronomy believe this was
caused by a comet hitting the earth and exploding in the upper atmosphere.
The debris from this giant explosion was such that it enveloped the earth in
soot and ash, blocking out the sunlight and causing the very cold weather.

This effect is known as a plume and is similar to that which was seen when
comet Shoemaker-Levy-9 hit Jupiter in 1995.

Historical references from this period - known as the Dark Ages - are
sparse, but what records there are, tell of crop failures and summer frosts.

The work was carried out by two Cardiff undergraduate students, Emma Rigby
and Mel Symonds, as part of their student project work under the supervision
of Dr Derek Ward-Thompson.

Their findings are reported in the February issue of Astronomy and
Geophysics, the in-house magazine of the Royal Astronomical Society.

The surprising result of the new work is just how small a comet is needed to
cause such dramatic effects. The scientists calculate that a comet not much
more than half a kilometre across could cause a global nuclear winter
effect. This is significantly smaller than was previously thought.

Dr. Ward-Thompson said: "One of the exciting aspects of this work is that we
have re-classified the size of comet that represents a global threat. This
work shows that even a comet of only half a kilometre in size could have
global consequences. Previously nothing less than a kilometre across was
counted as a global threat. If such an event happened again today, then once
again a large fraction of the earth's population could face starvation."

The comet impact caused crop failures and wide-spread starvation among the
sixth century population. The timing coincides with the Justinian Plague,
widely believed to be the first appearance of the Black Death in Europe. It
is possible that the plague was so rampant and took hold so quickly because
the population was already weakened by starvation.

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Received on Tue 03 Feb 2004 11:39:28 AM PST