Re: Extinction

[John Bois <jbois@umd5.umd.edu>]

On Fri, 24 Mar 2000 Dinogeorge@aol.com wrote:

> 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.

It is not accurate to say traces of iridium are traces of a "devastating
world-wide" event--unless you're claiming dinosaurs died from iridium
poisoning.  And other such effects have not been shown globally.  Even
fullarenes cannot kill dinosaurs as far as I can tell.

> 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.

Many things that are bagged into the mass extinction "event" occurred
before: pterosaurs, mosasaurs, ammonites experienced a cretaceous-long
decline, rudist clams.
Some/many extinctions are pseudo extinctions, the result of rapid
speciation (mammals, for example).
Specifically, among terrestrial vertebrates the ONLY group that
experienced true extinctions were the dinosaurs!  And, by the way, the
"boundary" at sea has not been exactly matched to the terrestrial
boundary.
And temporal clusters of extinction may occur as a purely statistical
phenomenon (shoot blindfold at the side of a barn and you will make
clusters).

> 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.

But these "alternatives" have solid evidenciary basis. Volcanism,
sea-level regression, mountain building, climate change, novel
speciation--these things really did happen!!
 
> We have measured the motion of the moon...

But many of the arguments revolve around the _difficulty_ of measuring
things that happened 65mya.  In your analogy, we cannot accurately measure
the motion of the moon; we can't tell which way it moves.

> 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.

But this assumption that the burden of proof is on this side is just
that--an assumption.  I assert the following: asteroids happen all the
time; evolution of mammaloids may be a once-in-a-universe event.  Timing
of dinosaur extinction occurs (where it is observed, at least) just at the
time of the evolution of Carnivora.  This clade, and others--I
hypothesize--have restricted the distribution of large egg layers ever
since.  In addition, predation is a well-known cause of extinction.  We
known nothing of any asteroid caused extinction.
Other hypotheses are respectable.  Habitat fragmentation recorded at the
K/T is another well documented agent of extinction.  So why this
favoritism to your favorite hypothesis?