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Re: astroblemes

I haven't been convinced either way over the atrobleme/extinction
hypothesis, so I'm not defending the "Earth First" position, just
trying to clear up some questions:

> From  pjanke@maroon.tc.umn.edu
> When you look at the fossil record over geologic time, the P/Tr *is*
> an abrupt event.  Many anti-asteroid theorists make the error that 
> everything has to die off in a very short time. The point you are missing 
> is that living organisms were comparatively stable for tens of millions
> of years before _and_ after the P/Tr or K/T boundaries. The faunal turnover
> that occurs at/around these boundaries *is* punctuation of equilibria. 

1. Why is it an error to assume that astrobleme extinctions require
quick die-offs? The environmental effects of astroblemes would last a
few years to perhaps a few tens of years at most. Critters that
survived the environmental effects would seem to be out of danger

2. I thought the point was made that living organisms were NOT stable
for the few millions of years before the proposed astroblemes, but were
already dying-off when the astrobleme struck.

> Regarding the hypothetical thinning of dino fossils leading up to the
> K/T boundary: Even if this were true, it's not much to base any conclusions
> on. NOTE: in the wake of the K/T impact(or _any_ large impact) there would 
> have been a period of rapid worldwide erosion. Midwesterners heard about 
> things like "hundred year flood" in the last few years. This would be 
> a once-in-50-million-year erosion event worldwide. Does Dr. Williams
> factor that into his model?

Don't know about Dr. Williams, but geologists in general do. The
thinning of dinosaur bones WOULD be conclusive. Rapid erosion (as would
be expected from an oceanic astrobleme impact) leaves its own kind of
signature known as an unconformity. The entire stratagraphic sequence
would be missing, not just the dinosaur bones. What the anti-astobleme
folks argue is that the rocks are there, but the bones are not.

> Ir anomalies have been documented at *all* of the above horizons. The
> further back you go in time, the more scant and confusing the data becomes 
> as the ratios between siderophiles change in poorly understood ways.
> Shocked quartz and/or microtektites have also been found at most, if not 
> all of the above horizons.

This seems like a contradiction. If the data are scant, confusing, and
poorly understood, how can *anomalies* be documented?

Care to clarify these arguments?

Andrew Robinson