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Re: "Forensic" Evidence Of Dinosaur Killer



jwoolf@erinet.com wrote:
>
><sigh> Another expert hypnotized by the Doomsday Scenario.  Doomsday
>impact theories are disproved by the fossil evidence.  Burn away the
>surface vegetation and you wreck the terrestrial ecosystem completely. 
>The ecological collapse shown in the fossil record is extensive,
>claiming all animals over about ten kilos in mass and many smaller ones,
>but it is _not_ complete.  Some groups survived.  And the survivors
>included a large number of small endothermic animals, which require
>_lots_ of food.  No plants, no food.  No food, all those little mammals
>and birds would have starved.  They didn't starve.  Ergo, there must
>have still been plants around. 
>
>Not convinced?  Consider oxygen.  Firestorm = lots of oxygen suddenly
>gone from the air.  It would have taken decades or centuries for the
>oxygen to build back.  In the meantime, what happened to all those
>oxygen-breathing animals?

There seems to be a substantial hole in your reasoning.  That hole is
approximately 300 km in diameter and is located in the Yucatan.  

The survival of some species disproves *some* impact theories.  However,
there was clearly an impact, and the effects could hardly have been less
than spectacular.  The fact that it was not universally fatal is also not
particularly surprising.  It comes down to an allocation of the energy
budget.  The incoming kinetic energy of the object could be dissapated in a
number of ways.  A good deal of the energy was necessarilly lost in  a
downward-directed shock wave.  This would have no drastic effects and would
only (a) heat the mantle and (b) change the momentum of the Earth by some
miniscule amount.  Additional energy would be lost in laterally-directed
shock waves, causing earthquakes and a tsunami.  Again, the results are
impressive but not catastrophic, except locally.  The evidence for a very
large tsunami is strong.  A third portion of the energy would go into
vaporizing water and rock locally.  Finally, some fraction of the shock
waves would rebound, resulting in the ejecta described in the article.  

We know very little about key parameters: the composition of the impacter
(rocky asteroid?, "dirty snowball" comet?), and the speed and angle of
impact, to name two.  Thus, its not really possible to determine what the
energy budget was.  However, we are here, which suggests an upper limit to
the ejecta effect.  The large hole in the ground, anomalous iridium, shocked
quartz, etc. (as well as common sense) set a lower limit.  

  --Toby White