Re: Large animal extinctions
Timo Niroma (timo.niroma@tilmari.pp.fi)
13 Jul 1996 23:15:13 GMT
In article <4rtt3b$de@hecate.umd.edu>, "Thomas R. Holtz, Jr." <th81@umail.umd.edu>
says:
>
>timo.niroma@tilmari.pp.fi (Timo Niroma) wrote:
>(snips)
>> continent shelves, are very difficult to investigate. So one possibili
>> ty is that the crater is deep in the North Atlantic out of the reach
>> of detectability.
>Except of course the seafloor has been radar mapped so that most large
>scale surficial structures are well resolved.
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.
Because there have been found about 150 meteorite craters on continents, there
should be 300 in the oceans. If we take into account only the youngest ones, which
is what the oceans could still preserve as detectable, there should be some 50 on
continents and about 100 on the bottom of oceans.
>>
>> b. The bottom of the Atlantic Ocean is moving about 3 cm per year,
>> which makes almost 400 m since the end of the ice age
>
>400m distortion of a 2-4 km object would still be a pretty circular
>structure. Also, the whole seafloor is moving together, and except at
>the transverse faults, there isn't a whole lot of distortion anyway.
>>(snips)
>>
I refer to the previous answer.
>> 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.
>> The smaller the animals the more shelter they
>> could get 65 million and 11600 years ago and the smaller the animal the
>> less food in average they needed.
>
>The trilobites died off 200 million years or so earlier, at the Permian-
>Triassic boundary.
The point is however that the smaller the animal the more was its chances to survive
unless the chain of food was also cut.
>
>> 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.
There may not have been a very great tsunami, if there was a great implosion after
the explosion.
>
>> As I already implied, all new hypothesis that contain odd features to
>> the recipients, may sound absurd to them.
>
>Illogical jump. Just because some hypotheses which were later accepted
>were first considered absurd does not mean all hypotheses which are
>considered absurd are later accepted.
>
That's true, of course. But I didn't say that "all new hypothesis that contain odd
features to the recipients, sound absurd to them." There was a "may" before the
"sound".
Friendly,
Timo
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