[meteorite-list] Hibben and YD impacts
From: Spaceguard <mail_at_meteoritecentral.com>
Date: Sat, 03 Apr 2010 01:44:06 +0100
Also, read this. Bill Napier is on the case.
The Spaceguard Centre
Was a giant comet responsible for a North American catastrophe in 11,000 BC?
Royal Astronomical Society Press Release
RAS PN 10/17
1st April 2010
For immediate release
Was a giant comet responsible for a North American catastrophe in 11,000
BC? (RAS PN 10/17)* *
13,000 years ago the Earth was struck by thousands of Tunguska-sized
cometary fragments over the course of an hour, leading to a dramatic
cooling of the planet, according to astronomer Professor Bill Napier of
the Cardiff University Astrobiology Centre. He presents his new model in
the journal Monthly Notices of the Royal Astronomical Society.
The cooling, by as much as 8?C, interrupted the warming which was
occurring at the end of the last ice age and caused glaciers to
readvance. Evidence has been found that this catastrophic change was
associated with some extraordinary extraterrestrial event. The boundary
is marked by the occurrence of a "black mat" layer a few centimetres
thick found at many sites throughout the United States containing high
levels of soot indicative of continental-scale wildfires, as well as
microscopic hexagonal diamonds (nanodiamonds) which are produced by
shocks and are only found in meteorites or impact craters. These
findings led to the suggestion that the catastrophic changes of that
time were caused by the impact of an asteroid or comet 4 km across on
the Laurentide ice sheet, which at that time covered what would become
Canada and the northern part of the United States.
The cooling lasted over a thousand years, and its onset coincides with
the rapid extinction of 35 genera of North American mammals, as well as
the disruption of the Palaeoindian culture. The chief objection to the
idea of a big impact is that the odds against the Earth being struck by
an asteroid this large only 13,000 years ago are a thousand to one
against. And the heat generated by the rising fireball would be limited
by the curvature of the horizon and could not explain the continent-wide
occurrence of wildfires.
Professor Napier has now come up with an astronomical model which
accounts for the major features of the catastrophe without involving
such an improbable event. According to his model, the Earth ran into a
dense trail of material from a large disintegrating comet. He points out
that there is compelling evidence that such a comet entered the inner
planetary system between 20 000 and 30 000 years ago and has been
fragmenting ever since, giving rise to a number of closely related
meteor streams and comoving asteroids known as the Taurid Complex.
In the course of the giant comet's disintegration, the environment of
the interplanetary system would have been hazardous and the Earth would
probably have run through at least one dense swarm of cometary material.
The new model indicates that such an encounter would last for about an
hour during which thousands of impacts would take place over continental
dimensions, each releasing the energy of a megaton-class nuclear bomb,
generating the extensive wildfires which took place at that time. The
nanodiamonds at the extinction boundary would then be explained as
having come in with the comet swarm.
One recent meteorite is known which may have come from this giant comet
progenitor: the Tagish Lake meteorite, which fell over Yukon Territory
in January 2000. It has the highest abundance of nanodiamonds of any
meteorite so far analysed.
Professor Napier sums up his model: "A large comet has been
disintegrating in the near-Earth environment for the past 20,000 to
30,000 years, and running into thousands of fragments from this comet is
a much more likely event than a single large collision. It gives a
convincing match to the major geophysical features at this boundary."
Professor Bill Napier
Mob: +353 (0)86 304 2636
E-mail: smawmn at cf.ac.uk <mailto:smawmn at cf.ac.uk>
Dr Robert Massey
RAS Press and Policy Officer
Tel: +44 (0)20 7734 3307
Mob: +44 (0)794 124 8035
E-mail: rm at ras.org.uk <mailto:rm at ras.org.uk>
FURTHER INFORMATION The paper will appear in journal Monthly Notices of
the Royal Astronomical Society. A preprint can be seen at
E.P. Grondine wrote:
> Hi all -
> I was wondering if anyone here would like to apologize to Frank Hibben:
> or to Dr. Firestone.
> By the way, the "blueberries" on Mars are impact vapor condensates, not water condensates.
> E.P. Grondine
> Man and Impact in the Americas
> Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html
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Received on Fri 02 Apr 2010 08:44:06 PM PDT