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From: lindsay@K.GP.CS.CMU.EDU (Donald Lindsay)
Newsgroups: sci.misc
Subject: Re: more Velikovsky
Message-ID: <1167@PT.CS.CMU.EDU>
Date: 19 Mar 88 03:45:35 GMT
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In article <5250@uwmcsd1.UUCP> markh@csd4.milw.wisc.edu (Mark William Hopkins) writes:
>>>The dinosaur-extinction hypothesis, as I understand it, is that dust
>>>raised by a large meteorite striking the earth caused climactic changes
>>>that the dinosaurs couldn't survive.
>>>Velikovsky's hypothesis was that the climatic change brought about by the
>>>near collision caused the mass extinction at the end of the Ice Age ... the
>>>very same kind of hypothesis.
>>
>>A planet floating by, and an asteroid ramming us, are not "the same kind of
>>hypothesis".
>
>In both cases we are talking about collisions or near collisions.

No. Read carefully. A planet floating by is a near-collision. It is not a
collision.  An asteroid ramming us is a collision. It is not a near-
collision. 

If an asteroid missed the Earth, it would have no serious tidal effect.  If
it grazed the atmosphere, it would do at most local damage. (A side note:
some mountain climbers once photographed a grazing meteor that was **going**
**up** ! ) The lack of damage follows from the fact that it retained enough
energy to escape, hence didn't leave the energy here. So, the asteroids that
do damage are the ones that collide. Their kinetic energy is turned into
heat, there is a shock wave, and material is flung clean into space. Dust
may take years to come out of the atmosphere, hence the climate can change
world-wide. The shock can cause local volcanoes, which put out dust, ditto.
Smaller asteroids may cause localized extinctions, just through the shock
(particularly if they hit an ocean and cause habitat flooding). However,
these smaller events are localized: the big ones, global.

A planet is maybe 10 to the tenth times heavier.  If a planet hit us, I
would expect no multicellular life forms to survive. If that. So, we are
talking about near-collisions, only, since life is in fact present.  All
interaction would be via tidal effects. (If the atmospheres mixed, then the
planets would have to be separated by about one percent of their diameters,
and the tides would shatter every continental plate.) So.  Let's look at
tidal effects. If the earth's rotation stopped and restarted (as Velikovsky
claimed) then volcanoes should have broken out simultaneously everywhere.
(Dust again.) Earthquakes everywhere should have flattened all the limestone
caverns that are in fact still there. Or, the near-collision could have been
at quite a distance, in which case the effects Velikovsky used as his
"evidence", wouldn't have happened. 

>This is another puzzle I pose to you, that I have already solved.  Find a
>mechanism that will circularize planetary orbits in a small time span.  No
>cheating, you can't use electromagnetic forces, only gravity.  Further, it
>has to be consistent with today's observations.

It also has to be consistent with the currently-best topographic map of
Venus, and its greenhouse effect, and its atmospheric composition, and its
rotation rate. Don't let me stop you trying.

>>There was no mass extinction at the end of the Ice Age.
>To the best of my knowledge, all the horses and camels (!) on this continent
>died out.  The mammoths became extinct, the saber tooth tiger, to name a few.
>I would call this a mass extinction.  In any case, this is what I am 
>referring to. Particularily the mammoths in Siberia.

A "mass extinction" is the extinction of a major fraction of all species in
the fossil record - like, 40% of them. At the end of the ice age, the
extinction was not massive at all. I have the impression that it was mostly
higher mammals, and that the extinctions were localized - American horses,
but not Asian, for example. Also, the last I heard, there was some reason to
believe that Man killed off e.g. the saber tooth tiger. Note that a near
collision with a planet should not have localized effects.
-- 
	Don		lindsay@k.gp.cs.cmu.edu    CMU Computer Science