🚀 go-pugleaf

It just so happens there is an article in the current issue of Nat'l 
Geographic (June, I think) that deals with mass extinctions.  It says that
most scientists now believe that the extinction of the dinasaurs was caused by
a single event as opposed to a gradual dying out.  They define the time
boundary of the Cretaceus (sp?) period (when there were dinasaurs) and the
Tertiary (sp?) period (when there weren't) as the K-T boundary.  There have 
been samples of quartz crystals found that date to around the K-T boundary
that show signs of stress to a degree such as that caused by a nuclear
explosion or an impact of a very large meteor.  
There has also been found a pencil thin layer in a chunk of rock of an element
commonly found in meteors but rarely on earth.  The layer in the rock where
this occurs corresponds roughly to the K-T boundary.  They estimate the meteor
to have been about 6 miles across which would produce the equivilent of
10,000 times all the world's nuclear explosives.

As for what happened after the impact, scientists differ.  Some propose that
90 % of the earth's forests caught fire.  Some say that if the impact were on
land it would produce a thick smog that would cause extreme cold; but if it
were at sea, it would send so much water vapor into the atmosphere that a 
greenhouse effect would produce extreme heat.  One scientist who has been
studying the Yellowstone fire proposes that even if the impact were at sea
it would have produced an explosion so great that most of the world would have
caught fire (I forget the specifics she detailed, but they were very
interesting).

Still others (but a minority now, I believe) maintain that the cataclysm
can be explained by earthly causes such as ice ages, volcanic activity,
shifting of the continents, etc.  But, there seems to be evidence that
suggests otherwise.
-- 
    ---{john hayes}  Old Dominion University; Norfolk, Virginia USA
                     internet: aiko@cs.odu.edu
                     Home: (804) 622-8348     Work: (804) 460-2241 ext 134  

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Are you a Have or a Have_Not?  Because if you're a Have_Not, you've probably
had it; whereas, if you're a Have, you've probably got it and are going to 
give it away at some point in the future!       --- The Clash
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