Re: Odd Observations (from T. R. Lipka)

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> We know that Ir is very mobile in the
>sediment and that it can be chemically concentrated at the base of >shale
>layers and at REDOX boundaries (see Wang et al., 1993 [Geology] >Sawlowicz,
>1993 [P3]).  Moreover, the fact that Ir anomalies appear in >demonstrably
>incomplete sequences suggests to me that chemical concentration >is more
>likely.

Norm points out a possible weak link in the use of Ir as definative evidence
for an impact. In addition to concentration/diffusion by biotrbation and
REDOX reactions,  there is the microbial factor. I believe it has been shown
that certain microbes can preferentially concentrate heavy meatals such as
Gold and Uranium and that some of the Ir concentrations may be attributable
to microbes as well. I don't think that any of the phenomena rules out the
use of Ir as a proxy for the "killer asteroid" . Iridium is very rare on the
earth (or in it) and the levels detected in many of the K-T and other
boundary sites indicate that it had to be brought in from beyond this planet.
In other words, something had to put the Ir  here and let's not forget Os,
Re, and other REE anomalies  for our bio-geochemical processes to affect.
Here we also need more investigation as to the extent to which these
phenomena play a role before Ir can be ruled out.

>  The sensationalistic seduction of
>explaining everything by a big fireworks display is very tempting >(and it
>makes excellent media copy). But good science can't be fit into >sound bites
>and it's going to take a lot of hard interdisciplinary work before we >get
>this part of Earth history properly sorted out.  To paraphrase Mark >Twain,
>"Rumors of a solution to the K-T extinction mystery have been >greatly
>exaggerated."


Seductive yes! Hyped and sensationalized by the MEDIA yes! But there is
_plenty_ of good science that has shown the impact occured  at roughly the
right time. Many  opponents now admit this. The extinctions are of course the
heart of the debate. Labelling the data as "bad science"  just because the
media took sides early on this issue does not detract from validity of the
science that was used to obtain the data  (now sensationlized  by thr media).
Maybe we should exclude the media from now so that they can't cloud the issue
 (i.e screw things up which is their predilection) since there is an
underlying problem of who's theory gets the most media and this admittedly
seems to add unnecessary bias and to some, ill feelings!!

                                         regards,
                                         Thomas R. Lipka
                                         Paleontological/geological Studies