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From: kgd@inf.rl.ac.uk (Keith Dancey)
Newsgroups: sci.astro,sci.space,sci.space.shuttle
Subject: Re: asteroid almost hits earth
Keywords: a thousand years?
Message-ID: <6235@nfs4.rl.ac.uk>
Date: 23 May 89 09:15:43 GMT
References: <256@ringwood.Morgan.COM> <3200009@hpindda.HP.COM> <4566@tekigm2.MEN.TEK.COM> <2635@ssc-vax.UUCP> <103026@sun.Eng.Sun.COM> <6101@nfs4.rl.ac.uk> <1128@unm-la.UUCP>
Reply-To: kgd@inf.rl.ac.uk (Keith Dancey)
Organization: Rutherford Appleton Laboratory, Informatics Department, U.K.
Lines: 49

In article <1128@unm-la.UUCP> hazel@unm-la.UUCP (Hugh Hazelrigg) writes:
>In article <6101@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes:
>>My understanding is that the demise of the dinosaurs extended over a period
>>of order of magnitude of a thousand years.  Certainly long enough to place
>>doubt upon the viability of a single catastrophy such as the one mentioned.
>
>What prevents the effects of a "single catastrophy [sic]" from propagating over
>a period of a thousand years?  On a geological scale of time, the events of a 
>thousand years constitute less than a footnote in a billion-page volume.  
>
True.  But you are forgetting that geology was not the issue in the
article on the relatively sudden extinction of dinasaurs.
The issue was whether a single impact could effect *meteriological*
conditions such that a species would become extinct.  For instance,
whether polluted skies would effect food chains and temperature.  But
if that scenario was to be true, then SURELY a species would die within
its lifetime.  If one dinosaur could survive its entire life under these
conditions, then so could another, and so on.  If dinosaurs took a 
thousand years to become extinct, what finished off the last one that
*didn't* manage to kill its immediate forbears.  If anything, one would
assume that survivors of the first five hundred years would have been
selected to manage better under the austere conditions, rather than
the opposite.  It is also reasonable to assume that these hostile
conditions would *gradually* improve with time, thus *increasing*
the chances of species survival, rather than the opposite.
>
>Look:  a thousand years (or even five or ten) really is just a one-nighter 
>(what a party!).  The earth may have lost a host of magnificent species, but 
>did life disappear?
>
When you are talking about *dramatic* changes in climate and food chains
critically effecting species survival, then the time scales involved must
be of the order of seasons, rather than thousands of years.  One year of
darkness is all that it would take to destroy vegetarian dinosaurs.  But
they lasted for generations.  How?  And if even a single generation could
survive lower temperatures, why couldn't others?

>I believe the metorite/asteroid collision theory to be the best put forward to
>date to explain the demise of the dinosaurs and their ecosystem. Your objection,
>Keith, is ill-considered.
>
Far from it.  There are enormous problems with a *single* catastrophy such
as an asteriod strike *if* the palaeontological evidence is to be believed
(unless dinosaurs lived a thousand years, that is :-).
-- 
Keith Dancey,                               UUCP:   ..!mcvax!ukc!rlinf!kgd
Rutherford Appleton Laboratory,
Chilton, Didcot, Oxon, England  OX11 0QX             
Tel: (0235) 21900   ext 6756                JANET:       K.DANCEY@uk.ac.rl.inf