Re: Extinction

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

>>Not exactly right. A mass extinction will have a single global cause, not
>multiple< causes.<<

Sorry I misstated.  When you said:
>>  Each mass extinction has its own cause, which need not be an asteroid
impact at all.  <<
I thought you meant that there could be different causes or combinations of
causes of mass extinction.  You do mean, if I understand you correctly, that
even though different causes of mass extinctions do exist, not just asteroid
impacts, only one cause can possibly apply to a single mass extinction.
This also implies, I take it, that mass extinctions cannot be produced by
aggregations of causes with limited or local effects.
I'm trying to think how this hypothesis could be disproved, in order to meet
the definition.  Presumably, if any other destructive event occurred around
the time of the single cause, this would be considered part of the
'background noise' of species arising and becoming extinct?  If you were
looking for the cause of the Permian extinction, for example, would you look
for evidence of a destructive event associated in time with the
disappearance of a sufficiently large number of species spread over a
sufficiently wide area and assume that that event must have produced the
remainder of the extinctions?
I'd appreciate any clarification you could provide.

>>If you say that this event and the K-T mass extinction had nothing to do
with one another and are purely
 coincidental, you have to show positively why you are denying the obvious
conclusion.<<

Please remember that my suggested restatement was:
>> 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.<<
I certainly wasn't trying to argue that the impact wasn't important!

>>It is not sufficient to merely list possible alternative causes of mass
extinctions and assert that they might have caused the K-T extinction
instead.<<
Agreed, definitely not 'instead'.  But if one of those alternative causes
existed, then it would be possible to argue that this cause contributed to
the mass extinction, and therefore the impact was not the sole cause.
However, this runs counter to your statement that
'A mass extinction will have a single global cause, not  >multiple< causes.'
I do want to understand this statement better before making further
responses to your discussion.
Thanks!

----- Original Message -----
From: <Dinogeorge@aol.com>
To: <philidor11@snet.net>
Cc: <dinosaur@usc.edu>
Sent: Friday, March 24, 2000 12:41 PM
Subject: Re: Extinction


> In a message dated 3/24/00 8:21:22 AM EST, philidor11@snet.net writes:
>
> << 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. >>
>
> Not exactly right. A mass extinction will have a >single< global cause,
not
> >multiple< causes. One such single cause can be asteroid impact. The
problem
> with multiple causation is to get all the causes to coincide in their
> effects; the more causes you throw into the mix, the less chance there is
> that your hypothesis will stand. The asteroid impact at the K-T boundary
was
> gigantic, with devastating worldwide physical effects whose traces have
been
> well documented in the geological record. If you say that this event and
the
> K-T mass extinction had nothing to do with one another and are purely
> coincidental, you have to show positively why you are denying the obvious
> conclusion. It is not sufficient to merely list possible alternative
causes
> of mass extinctions and assert that they might have caused the K-T
extinction
> instead.
>
> We have measured the motion of the moon and have found that it orbits the
> earth from west to east. If you come along and assert that it really moves
> from east to west, and that what we have been measuring is some kind of
> illusion, it is up to you to demonstrate this. Similarly, anyone who
denies
> the connection between the K-T mass extinction and the K-T asteroid impact
> must now >show<, not merely >assert<, that these events are disconnected
and
> coincidental. (One way to do this, for example, might be to exhibit
> unreworked dinosaur fossils from well above the K-T boundary.)
>