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Re: Dino extinction



pjanke@maroon.tc.umn.edu wrote:
 > 
 > Sherry Michael wrote:
 > >Sure, maybe a catastophe. Did it cause the extinction? Were not even sure
 > >it was a extraterrestrial body. ...
 > 
 > Sherry, I'm curious. How much research have you actually done on this?
 > I have a theory that if people would only become familiar with the latest
 > published research on the K/T, they would overwhelmingly support the
 > bolide theory.

Well, I am going to have to call you on this one.
Whether she has done alot of research or not, *I* have.
I am *not* convinced of the bolide theory.  Even *if*
the Chicxulub site really *does* turn out to be an impact
crater at the boundary (currently quite doubtful), I would
not be convinced that it was the primary cause of the extinction.

The pattern of disappearance of many groups, including that
of the dinosaurs, at least in the Lance/Hell Creek beds of
the USA, does not fit that model, for one thing.  And if the
pattern found in the Hell Creek beds is found in other areas
of the world, this would pretty much eliminate any possibility
that an impact was the primary cause.

 > There is simply no other way to account for the anomalous
 > values of the thing you casually brush off as "some trace element". It
 > happens to be Iridium, which is relatively rare in the earth's crust but
 > common in asteroids and comets. (There are actually a group of elements 
 > like this called siderophiles.)

True, and not only that but the elemental profile of the siderophile
spike at the marine K-T boundary is characteristic of extra-
terrestrial siderophiles.  (Most of the other siderophile spikes
I know of show a different elemental profile, one that is consistant
with volcanogenic origin).

However, just because some bolide hit the Earth during the same
span of time as extinctions were occuring does *not* prove it to
have been the primary cause of said extinctions.

Coincidences *do* happen, and bolide impacts are actually fairly
common on a geological time scale.

 > Ten years of research has added an
 > enormous amount of discoveries which bolster the Alvarez conclusion.

Which bolster *part* of their conclusions - the occurance of some
sort of ET impact.

Even in the marine realm, many groups show a decline in diverstity
*prior* to the impact.

 > ... 
 > tsunami deposits around the Gulf of Mexico,

Well, last I heard, the supposed tsunami beds were highly
questionable - they were apparently both earlier than the
K-T boundary, and probably not tsunami beds.

Furthermore, since at least one of the supposed tsunami beds
shows a stepwise loss of marine brachiopod species *prior*
to the erosion layer (whatever caused it), placing the hiatus
*before* the K-T boundary makes the extinctions even *more*
gradual than placing it at the boundary.

[Note, I am still not entirely sure that I accept the contrary
evidence for the cause and timing of these beds - at least not
until I have had a chance to evaluate it in more detail].

 > the soot layer part of the 
 > boundary clay in some areas.

Soot layers are common - forest fires were a widespread phenomenon.

Now, the fern spore spike is a different matter, as that indicates
a nearly total elimination of woody vegetation over a very wide
area of North American at the K-T boundary.

 > There is so much corroborating evidence for
 > the Chicxulub impact that it's frankly getting difficult to understand 
 > why there is even a dispute about whether an impact occurred.


Even if an impact *did* occur (though quite possibly *not*
at Chicxulub), this does not make it the primary cause of
the extinction.

 > 
 > [ref to the Chicxulub impact crater]
 > Sherry Michael wrote:
 > >There is increasing doubt that it is an impact site at all. 
 > 
 > BZZZTTT! Wrong. Thank you for playing. You should have said *decreasing*
 > doubt that is an impact site.

Sherry was right to start with.

There has been a recent (last 5 months) reversal on this.

New evidence has come to light of intact latest Cretaceous
sediments *inside* the supposed impact structure.  If this
is indeed true, and is verified by other workers (who are
going to immediately try to discredit the new evidence),
this pretty much scotches Chicxulub as a due to a K-T
boundary impact.

Note, this is still merely doubt - until the find has been
verified by independent researchers it is still possible it
is an error in sampling or identification (even if that is
unlikely, such things have happened).

This was published in "Geology", the news rag of the Geological
Society.

 > But don't believe me, I encourage readers 
 > out there to read about it for themselves in Science, Nature, Science News, 
 > Earth, Discover, Scientific American  or whatever they read.

Try reading more than that.  Except for Science and Nature,
these tend to be months or years behind the current results.

 > However, only a few scattered teeth have been found in Tertiary deposits,
 > and from the context were explicable as having eroded from Cretaceous rocks.

Yes, they were explicable as such, though the finder of one such
set claims they did not show the type of scratching and pitting
one would expect from re-deposited teeth.

Also, note, the abundance of teeth drops drastically several meters
*below* the boundary clay - at about the same level as dinosaur
bones become seriously scarce, the so-called barren zone.

So, at best this evidence supports a pattern of extinction spread
out over a longer period of time, and largely complete at the
time of the impact.

[This is the pattern I was talking about above, which if found
in places other than the Hell Creek beds would blow away any
possibility of the impact being the primary cause].

 > I assume you are looking for some evidence that the end of dinos does not
 > correlate to the K/T boundary clay. There is sufficient sampling to state
 > that few, if any dino fossils occur above the K/T boundary.

However, there is also sufficient sampling, at least in the
Hell Creek beds, to say that very few dinosaur bones indeed
occur in the last 2-3 meters *below* the boundary as well. 
 > 
 > Maybe someday, Sherry, you will pick up an old Scientific American
 > and look closely at the nice full-page color photo of the Gubbio, Italy
 > K/T section. You will notice the forboding, black, Iridium-rich boundary
 > clay sandwiched between otherwise nice, white marine carbonate rock.

Yep, so what?  All that shows is that the marine extinctions
were relatively abrupt.  This is also, as you say yourself,
old data.  In science it is the new data that is most important.



I am *not* going to repost my summary of the evidence that
extinctions in general are *multicausal*, and usually associated
with flood basalt style volcanism.

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

The peace of God be with you.