Re: K/T impact (was Re: [for some reason] Tim's theory)

["Tim Williams" <twilliams_alpha@hotmail.com>]

John Bois wrote:

> No, I'm going to tell you that science progresses by rigorous examination
> of alternate hypotheses; that the bolide hypothesis for marsupial
> extinction is weaker on its face than competition with placentals [snip]

Maybe both happened: Placentals were nudging out marsupials when the bolide 
hit.

> 3) bolide-caused extinction of any organism has not been
> observed and may be untestable

I hope to God we don't "observe" a bolide-caused extinction any time soon.

> (this doesn't mean it didn't happen--just
> that obserable phenomena that can explain things are preferable to
> unobservable phenomena than can explain things)

This is quite nonsensical.  Our judgements on the relative likelihood of 
competing scenarios should not be limited to what we, as humans stuck in a 
particular time and place, can see and touch directly.  The Big Bang is not 
an "observable phenomenon", but I like to think we can infer the fact that 
it happened from existing scientific data - without having to build a time 
machine and watch the Big Bang unfold before our eyes.


> Then, if you subtract marsupials, and birds from the "mass" extinction,
> you do not have such a massive extinction and you lose the kind of
> umbrella explanation-for-everything provided by uncritical examination
> of bolide theories.

Birds were totally unaffected by the K/T extinction?  Maybe (as Ken says) 
the diversity of modern birds are descended from a handful of neornithine 
species that some how survived the calamity.  Toothed birds were not so 
fortunate.

In the seas, forameniferans, coccolithophorids, belemnites, ammonites, 
nautiloids, bivalves (such as reef-building rudists), brachiopods, all 
plummeted at the end of the Cretaceous, and not all had recovered by the 
Tertiary.  Some (like the forams) regained their abundance, but most were 
never the same again, and some disappeared forever.

On land... well, we know what happened there.


Tim





------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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