Re: Extinction

["philidor11" <philidor11@snet.net>]

>>  Each mass extinction has its own cause, which need not be an
 asteroid impact at all. But the cause of the K-T mass extinction >is< an
 asteroid impact, beyond reasonable doubt.<<

Restating your assertion:  A mass extinction can have multiple causes, among
them an asteroid impact.  The K-T mass extinction occurred at approximately
the same time as an asteroid impact.  Therefore, the K-T mass extinction was
caused by an asteroid impact.

Reasonable doubts can, it seems to me, be produced by any of the following:
1.  A substantial portion of the extinctions occurred before the impact,
2.  Another cause or other causes of mass extinction (each having a limited
but significant effect) have been observed at about the same time,
3.  Effects of the impact were not severe enough somewhere to produce
observed extinctions,
4.  An impact does not produce an effect sufficient to cause extinction of a
substantial group of animals or plants which did go extinct,
5.  A specific effect caused one species to become extinct while another,
equally vulnerable to that effect, did not, and
6.  Breeding populations of a substantial number of affected species
continued long enough after the extinction to be eliminated by another
cause.
The assertion seems vulnerable.

To me, it seems more appropriate to say that the K-T mass extinction may
have had multiple causes, but an asteroid impact was at least most prominent
among these causes.

We've both commented on cladistics' reliance on parsimony to determine
evolutionary relationships.  Here too simplicity of explanation can't be
used as a complete justification, I think.





----- Original Message -----
From: <Dinogeorge@aol.com>
To: <philidor11@snet.net>
Cc: <dinosaur@usc.edu>
Sent: Friday, March 24, 2000 2:36 AM
Subject: Re: Extinction


> In a message dated 3/24/00 0:34:28 AM EST, philidor11@snet.net writes:
>
> << '...cannot be the result of a coincidence...'?  Less ...um...
parsimonious
>  than a single cause, yes, but probability does not preclude coincidence.
If
>  you want to rule out coincidence in principle, then first you have to
find
>  direct evidence of an impact at the time of each major extinction.  The
>  argument that simultaneous extinctions prove impacts because impacts
produce
>  simultaneous extinctions is false without a demonstration that in reality
>  ONLY impacts can produce simultaneous extinctions. >>
>
> Not true at all. Each mass extinction has its own cause, which need not be
an
> asteroid impact at all. But the cause of the K-T mass extinction >is< an
> asteroid impact, beyond reasonable doubt. The burden of proof is now on
those
> who continue to assert that the asteroid impact did >not< cause of the K-T
> mass extinction to present their evidence, which so far has been nothing
more
> than hand-waving, implausible alternative hypotheses, a pack of
coincidences,
> and/or just-so-story scenarios. As far as other mass extinctions are
> concerned, their causes may or may not be asteroid impacts, and they are
> largely irrelevant to the cause of the K-T mass extinction.
>