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Re: Asteroid impact finally confirmed?



Stan Friesen wrote:
> 
> From: Jonathon Woolf <jwoolf@erinet.com>
>  > Finally, sediments showing a more normal rate of fossilized animals.
> 
> Containing what fauna?  A depauperate Cretaceous fanua?  A low
> diversity early Paleogene fauna?  A full diversity fauna of some
> sort?  [This is a critical point in arguing that this impact
> was the *cause* of the extinctions].
> 

The article I saw didn't make this clear, but I'm assuming it was a
low-diversity Paleocene fauna.

> 1. Even the largest most devatating explosion will not have uniform
> effects over even a single continent, let alone the entire Earth.
> Mountains, canyons, isolated seas, undersea ridges, and many other
> things will partially protect many areas.  Also there is powerful
> evidence that the impact was asymmetrical, with the strongest shock
> going northwest towards the American midwest and northwest coast.
> Thus many things in may [paces will survive, as small local populations.
> 
> 2. The full effect was not due just to the initial holocaust,
> but also to the persistant climatic effects from the aerial debris.
> This phase may well have lasted several years.  Thus the final extinction
> of most species will be due to the inability of the small remnant
> populations to cope with the changed climate.  The survivors will
> be those species that can cope with the change even at small population
> sizes.
> 

I agree these sound convincing -- except, if this is what happened, then
why do the extinctions appear to be simultaneous all over the world? 
All dinosaurs everywhere vanish at the clay layer -- whack, dead.  All
pterosaurs everywhere vanish at the clay layer -- whack, dead.  All
ammonites everywhere vanish at the clay layer -- whack, dead.  Etc.  No
remnant populations of any of them, anywhere.  In fact, I don't know of
any example from any site anywhere in the world of Cretaceous and
Paleocene fauna mixing, as if "remnant" Cretaceous species were mixing
with or evolving into Paleocene species.  AFAIK, virtually the entire
Cretaceous fauna vanishes at the clay layer, and when sedimentation and
fossilization resumes, it's all-new species, clearly related to what was
there before, but just as clearly different from what was there before. 
I'm perfectly willing to write that off to my own lack of information
about Paleocene sites, if somebody can give me some info on such a site,
or a reference to chase down.  But for now, it seems an extremely
puzzling anomaly.

-- JSW