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Re: asteroids and dinosaurs
Royan Webb wrote (4/27/96; 12:02a):
>On 25-Apr-96 21:11:51, Tompaleo said:
>T> Until we find a skeleton that shows some indication of being crushed
>T> by something or buried alive by impact affected material, one can
>T> only speculate about direct impact casualties.
>I have wondered why there isn't a large number of fossils at the time
>of the extinction. If it was a catastrophic die-off, I would think the
>number of remains would be much greater.
First of all, the impact layer is only a few cm thick in most places.
Not adequate for crushing a dinosaur or for burying one.
I have had students who say they won't believe the impact scenario until
we find concentrations of scorched dinosaur bones at the K-T layer!
The number of carcasses must have been very great at first. But you need
to think about _preservation_ of those remains. Some time ago I conjured
up some numbers, derived from scads of unverifiable assumptions, about
how likely it was for a dinosaur to have been preserved in a place where
we could find and collect it. I won't go through it all. Try it
yourself, and I'll bet you will end up in the same ballpark, or at least
the same major league city as me. I estimated ONE dinosaur every 80,000
years, on the average, was preserved where it could eventually have been
collected by now. I'm talking good skeletons only (see?--a lot of
assumptions, and also restrictions). I added some additional
considerations based on more unverifiable assumptions to concludce that
the odds of any individual dinosaur skeleton ending up in a museum was
about one in 80,000,000,000. Future collecting will improve the odds a
bit, but the bottom line is that it would have been more likely for a
dinosaur to win the state lottery than to get fossilized. So I am not
surprised that we don't find dinosaur skeletons impaled by meteorites.
On firmer footing, but perhaps just as debatable, Greg Retallack has
suggested that years of acid rain from the effects of a bolide collision
would have destroyed any skeletal material in the soil or other surficial
deposits. In spite of intensive searching, the upper 2 m or so of
Cretaceous sediments below the K-T layer have been found to be devoid of
dinosaur remains. I don't know if that's true for invertebrate material
as well, but it would have to be for Retallack's hypothesis to be true.
Norman R. King tel: (812) 464-1794
Department of Geosciences fax: (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712 e-mail: firstname.lastname@example.org