Re: Large animal extinctions
Thomas R. Holtz, Jr. (th81@umail.umd.edu)
15 Jul 1996 14:52:14 GMT
timo.niroma@tilmari.pp.fi (Timo Niroma) wrote:
>
> In article <4rtt3b$de@hecate.umd.edu>, "Thomas R. Holtz, Jr." <th81@umail.umd.edu>
> says:
>
> I know of one satellite mapping project. Maybe you refer to it.
> The resolution of it is at best 10 km and I know of no effort been made to find
> meteor craters via it.
>
> From the space shuttles there has been at least some attempts to find craters on
> continent.
>
> It is a very difficult task even on continents, but several have still been found.
Not satellite, sonar mapping from ships and submarines (sorry about mentioning
"radar" rather than "sonar" to begin with: didn't mean this to be
too confusing).
The sonar maps have quite an excellent resolution.
> >> The dinosaur-killer 65 million years ago left after it no animals whose
> >> weight exceeded 23 kg.
> >
> >Except for turtles, crocodilians, champsosaurs, and lot of fish.
> >
> This does not imply anything concerning the smaller ones.
>
> In fact the extinction was 100% in the above category and very selective in the
> below category.
As a vertebrate paleontologist specializing in Late Cretaceous terrestrial
vertebrates, the "100%" number you've heard is false. Some of the
crocodiles, turtles, and champsosaurs which survived were bigger than
23 kg, as were some of the fish.
> >
> >> Plant fauna near the epicenter is of course burnt by the tremendous heat,
> >> but the seeds in the ground survive, as can be seen after forest fires.
>
> >Where is the evidence for the fires? There are no known vast contemporaneous
> >ash beds from this geologically recent interval. For that matter, there
> >is no evidence for basinwide tsunami
>
> What ash there were, were surely washed into the Atlantic Ocean, when the Laurentide
> ice sheet melted.
Sorry, but the North Atlantic is one of the most heavily cored ocean
basins in the world. If the ash were all redeposited there, we'd have
found it. It isn't there. We have mud, marine fossils of all kinds,
even very small rocks (ice rafted debris) in some intervals, but no
big ash layers.
This is a very well studied interval of geologic time, with hundreds
of people worldwide working on it. Working for four years on marine
microfossils of the last 3 million years doesn't make me an expert, but
I do know the field fairly well. If there had been the sort of environmental
destruction you advocate in this interval, it would have left clear
evidence. Unfortunately, it isn't there.
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