[no subject]

The Deccan Traps (note the capital on the word "Traps") are a thick
deposit of basalt covering most of east-central India.  In places
they are several kilometers thick.

They were produced by massive volcanic flows without associated
explosive or ejective eruptions.  This sort of volcanism produces
extensive *sheets* of lava hardening into basalt.

Similar flood basalts (layers of laval sheets) are found in Idaho
(Craters of the Moon Park), Siberia, Antartica, and a few other
places.

Volcanism of that sort is not occuring anywhere on Earth at this
time (although Iceland may be somewhat similar).

The interesting thing about flood basalts is that there are known
flood basalt deposits that correspond in time to almost all of the
established Mesozoic extinction events.  The Siberian Traps match
the P-T extinction, the Antarctic basalts match another one (perhaps
one of the Late Triassic ones), and so on.

A good reference on this is the article by Jennifer Kitchell
in:     Extinction Event in Earth History
        E.G. Kauffman & O.H. Walliser (eds).

 >
 > > Combine this with the cooling climate, the lowering shelf seas
 > > (for marine organisms), and as a final blow, the Chicxulub impact,
 > > and you get a fairly good multi-causal model for the extinction.
 > >
 >
 > Chicxulub "impact?" I hear of late new theories saying it may be
 > volcanic, due to the layers of melted materials under the impact
 > site are not deep enough for a meteor that size.

I, too, have heard that.  I am not yet convinced, though the
data I have seen look strong.  The evidence that the feature
is impact related is also strong.  More work needs to be done
to reconcile the two sets of data.

If Chicxulub is not an astrobleme, then there is no candidate
impact site left.  (Manson is too small, and too early).

This would actually cast doubt on the existance of an impact.
Certainly, if Chicxulub is volcanic, it is not relevent to the
extinction (a single volcano, no matter how large, is insufficient
to impact species on a global scale).
 >
 > Something that always bothers me about the meteor theory:
 >
 > 1) as Bakker points out, what about animals like frogs that are very
 > dependent on conditions such as temperature and acid rain storms?
 Why did
 > they make it?

Hibernation?  Less acid rain than is often assumed?
Or, the frogs were not in decline already, and so not vulnerable
(see below).
 >
 > 2) Just because a meteor fell someplace does not make a direct
 cause-effect
 > relationship. Maybe it was just a fluke one fell when the dinosaurs
 were
 > dying out.

I would say that an impact of that size during a time of severe
environmental strees (of a sort that could lead to extinctions)
would have a severe impact on the already stressed populations,
making what might otherwise have been a minor or moderate extinction
into a major one.

In other words, the impact would merely be the last of a series
of crises - the last straw that broke the camel's back.  By itself
it might have had little effect  (much like the similarly sized
mid-Eocene impact).

An important point to note is that the extinction was selective
in several very interesting ways.  Among macroscopic animals, it
hit large forms more severely than small, and more specialized
forms more severely than generalized forms.  Among marine plankton
and the like, the extinction hit the tropics far harder than the
poles.

This suggests that to the extent the impact had an effect, it
basically amplified an already occurring process, and that only
groups already under stress were finished off.

 > I don't want to see some hole and say, "look this is the one
 > that did it!" I want someone to show me proof a meteor killed
 > off dinosaurs.

Then you will have a long wait.  Science doesn't deal in proof,
only in evidence.  If the extinction really was abrupt, and
exactly correlated with the impact, then there would be little
doubt about the causative nature of the impact.

The key thing to be determined is whether the extinctions
were spread over an prolonged interval of time, or were
abrupt.  The evidence is equivical on this, though for
dinosaurs in the Lance/Hell Creek beds it currently favors
an process spanning an interval of about 2-300,000 years.
[The "barren interval" between the highest abundant bone
and the iridium layer].  This, if confirmed, would fairly
well rule out the impact as the *sole* cause (though the fact
that it seems to be the terminus would seem to support it as
a contributing cause).
 >
 > 3) Are we running around looking for easy-answer craters instead of
 > looking for why the dinosaurs died out??

Of course, if there was no impact, it is difficult to explain
the Iridium layer.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.