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Re: the cause(s) of MASS extinction

In a message dated 98-08-15 09:30:59 EDT, jbois@umd5.umd.edu writes:

<< And I claim the only thing that made it exceptional was the extinction of
 non-avian dinosaurs.  And we _do_ need an exceptional cause for this.  But
 I don't believe the bolide provides one. >>

No, what was exceptional was the extinction of >all< the "non-avian" dinosaurs
>at the same time<. There is an exceptional cause for this, and it is the
asteroid impact. In a mass extinction, it is the simultaneity of hundreds or
thousands of extinctions that requires explanation, not necessarily the
extinctions themselves (whose individual explanations would naturally fall out
of the former). There is no way that so many extinctions would occur within
such a short span of time if they had happened independently, as if they were
the usual background extinctions that occurred here and there from time to