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Re: K/T impact (was Re: [for some reason] Tim's theory)
On Wed, 16 May 2001, Tim Williams wrote:
> Maybe both happened: Placentals were nudging out marsupials when the bolide
> >(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.
I agree with everything you say here (except the
"nonsensical" comment). But the example you've mentioned actually does
have direct evidence. There is _no_ evidence of causation for any
extinction around the K/T. It depends entirely on timing. But the timing
is not known for many species, and for others, thoroughly respectable
alternate hypotheses have been offered. I have just read a book called
"Ghost Species"--it cites Daniel Janzen's studies of fruit rotting in
Costa Rica--the assumption that it was produced for an extinct species is
valid--we have the bones to verify that likely species existed. But this
is _not_ what we are talking about. The claim that the bolide killed
marsupials and left placentals untouched strikes me as completely
fanciful. And what evidence could you bring to convince me
otherwise. Don't say: "because lots of other things went extinct at the
same time." This is circular--I can never escape this hypothesis--it
explains everything but nothing.
> 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
Again, the complete lack of _any_ suggested mechanism for killing off one
entire clade and letting another survive is damaging to this bolide
hypothesis! "...somehow survived" is saying it was a freak
accident. And, I suppose, marsupial extinction was another freak
accident. The bolide hypothesis seems to rest heavily on freaks.
> On land... well, we know what happened there.
Wait, I thought that was what we were arguing.