[meteorite-list] Hibben and YD impacts

[Spaceguard]

Also, read this.  Bill Napier is on the case.

Jay Tate
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." 

CONTACTS

Professor Bill Napier

Cardiff University

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 
http://arxiv.org/abs/1003.0744

E.P. Grondine wrote:
> Hi all - 
>
> I was wondering if anyone here would like to apologize to Frank Hibben:
>
> http://www.nature.com/news/2010/100331/full/464657a.htmlp
>
> 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
>
>
>       
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