Re: Large animal extinctions caused by early man
Timo Niroma (timo.niroma@tilmari.pp.fi)
5 Jul 1996 23:49:07 GMT
In article <Pine.OSF.3.92a.960705130324.12878A-100000@saul6.u.washington.edu>,
Scott Barboza <barboza@u.washington.edu> says:
>On Thu, 4 Jul 1996, Richard C. Schmidt wrote:
>(snips)
>> The fact is, the was a change in the climate 10-12,000 years ago.
>> We know this! The ice age ENDED!!!! Whether this was quick, in a
>> period of 1-3 years or less, or somewhat longer, is essentially
>> immaterial. IT HAPPENED!
>to be careful of terminology here. The ice age is, of >course, the Quarternary
ice age and the Earth is currently in the midst of it. It did not end ~10,000
>>(snips)
>Why did all of these extinctions happen only after the last
>ice advance to species which wheathered all of the previous advances and
>retreats without any problem at all?
>( snips)
>> As to why the ice age ended, the climate changed, we, at present,
>> have NO DIRECT evidence! We open to suthe great guessing game.
>> A moderately sized metorite impact in the middle of the Atlantic
>> is as good a reason as any I've seen so far.If anyone else
>> has a theory, please put them forward. I've seen writings
>> about the effects, BUT this is the first guess as to the
>> cause!!!!!!!!!!!
>>
>> ~~ Richard C. Schmidt
>Didn't Milutin Milankovitch propose a celestial mechanics mechanism in the
>late 1920's or early 1930's? I assume that most readers here are
>familiar with Milankovitch cycles.
>Scott Barboza
>University of Washington
>Department of Geological Sciences
>
1. Whether we have today an ice age is a question of definition.
Because there are huge ice sheets on Greenland and Antarctica we can say so.
The question has however normally been solved pragmatically: the amount of ice
that existed when man began to build his great cultures is regarded as normal
although from a geological viewpoint we live in an ice age, if an iceless Earth is
the only alternative.
However the temperature has for the last 11600 years been higher than any time
during those oscillations that lasted 100,000 years and are called an ice age.
We must go back to the Eemian interglacial some 120,000 years ago to get
temperatures that equal ours or even are higher than today.
2. When the Eemian began, there were no great extinctions.
One could say that there were men capable of hunting also at that time, but more I
believe in the Milankowicz cycles.
There is no evidence that men were capable to drive the megafauna into extinction
11600 years ago, and yet the megafauna of North America and Siberia went into
extinction.
What's the difference?
I can't prove definitely my impact theory, only make it very probable. And it is
explanation enough. Neither can you disprove it. Or claim that such an impact
wouldn't have been capable of making a great havoc.
3. I have very much studied the Milankowicz cycles. Partly they explain the ice
ages very well, partly not.
The Milankowicz cycles predict no catastrophe ends unless we enlarge it with some
kybernetic positive feedback mechanism.
The end of Pleistocene was very sudden and very powerful an event. Besides
according to Milankowicz cycles its end should not have occurred 11600 years ago.
Better estimate is 10,000 years later or very recently.
Regards,
Timo
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