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

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.



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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