[meteorite-list] Re: Crackpot impact theory

[Marco Langbroek]

Two things in particular, plus a few others, made me frown about this 
hypothesis. One is the "comet coalesced from supernova material". That's just 
not the current idea of how comets formed. So I do hope that Firestone in his 
paper provides a scientificaly viable mechanism for this alternative comet 
formation theory, otherwise it is crackpot.

The other point is, that mammoths did *not* get extinct all at once at ~13 000 
BP. On Wrangel Island in the arctic for example, they survived untill 4000 BP. 
In Eurasia, they disappear between ~15000 and 12000 bp, in what seems to be a 
gradual process.

Also, why the mammoths, but for example not the bears and bizons? Are bears and 
bizons immune to comet impact? The extinction of part of the megafauna at the 
end of the Weichsel/Wisconsin glacial is *not* akin to the mass extinctions of 
life such as at the K/T boundary (and it is not abrupt). And its not restricted 
to North Amerca, which seems the focus of this new hypothesis if the press 
release is correct ("comet impact in North America").

And where's the crater? We are talking here, of a comet the size of the K/T 
impactor (10 km). That leaves one giant crater, Chixculub sized.

These are just some legitimite questions based on scientific data we have, 
regarding this hypothesis. Since I have never been a fan of the "human hunting 
overkill hypothesis" either (another alternative hypothesis), my cards are still 
on the changes in environment happening at the end of the last glacial.

Note by the way, that a viable mechanism for peaks and lows in atmospheric 
radiocarbon, is in solar activity. Hence, a supernova certainly is not "the 
only" phenomena that explains it. In fact, current research suggests there are 
several cycles in atmospheric 14C levels over time, which implicates cycles in 
solar activity (the 11 year cycle is well know, but there are several longer 
cyces too, it appears).

- Marco
   (Pleistocene archaeologist)

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Dr Marco Langbroek
Dutch Meteor Society (DMS)

e-mail: meteorites at dmsweb.org
private website http://home.wanadoo.nl/marco.langbroek
DMS website http://www.dmsweb.org
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