Re: Extinction

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

At 21:59 2000-03-22 -0800, Stanley Friesen wrote:
>At 09:59 PM 3/21/00 -0500, John Bois wrote:
>> > 2) Nonetheless, if a bolide hit, and apparently one
>> > quite definitely did, there were a lot of unlucky
>> > frogs on that day.
>>
>>But there is _no_ evidence of this.  How can you say ot happened if you
>>have no evidence.
>
>Actually, there is a *great* *deal* of evidence that a bolide struck the 
>Earth at about 64 MYBP.  There is a probable crater, there are impact 
>tektites, there are enrichments in sidereal elements, there are now 
>fullerenes with sidereal elements trapped in them from the boundary.  Now, 
>*given* such a major bolide strike, it is *certainty* that it killed many, 
>many frogs, at the very least those living near where the bolide 
>landed.  This is a simple matter of physics - no living thing could survive 
>anywhere *near* the impact site.
>
>The debatable issue is whether the impact was, by itself, a *sufficient* 
>cause for the total extinction of non-avian dinosaurs.  (For instance, I 
>suspect that the bolide was so effective only because the ecosystems of the 
>Earth were already stressed from other causes, and the same bolide striking 
>at, say, 34 MYBP would have had little long-term effect).
>
Actually I think it would have had a great deal of effect at 34 MYBP, since
that would be right at the Eocene/Oligocene border, Stehlins "grande
coupure" when earth's ecosystem were probably a great deal *more* stressed
than in the late Maastrichtian.

Personally I find it hard believe it is justa coincidental that the P/Tr
extinction happened exactly at the same time as the largest volcanic
episode of the Phanerozoic and the K/T one exactly at the same time as the
largest bolide impact of the Phanerozoic.

Tommy Tyrberg