🚀 go-pugleaf

In article <6235@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes:
: 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.

Yes, but that's not really the issue.  To guarantee eventual extinction
you only have to reduce the rate of survival (to reproductive age) to
less than 2 per dinosaur family.  We all know that changes in
temperature affect fertility, not to mention fecundity...   :-)
And there could well be some relationship between temperature and
mortality.  Especially with large egg layers.  So meteorology can
certainly have long term effects on a species.

(What actually happened was the dinosaurs had an industrial revolution with
all the iron in the asteroid, and the standard of living went too high,
and too many of them became dinks.)

: If dinosaurs took a 
: thousand years to become extinct, what finished off the last one that
: *didn't* manage to kill its immediate forbears.

Probably loneliness.    Only 1/3 :-)

: 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.

There are several things to say about that.  If you trigger a mini ice
age it could well last longer than 1000 years.  Moreover, as the
dinosaurs get sparser, it becomes more difficult to find a mate and
de-sparsify the dinosaurs, a nasty form of feedback.  And even if
conditions are improving gradually, the land is now overrun with little
varmints who have a faster selection cycle and took advantage of the
new conditions while the bigger folk were still squeaking by.  Perhaps
the initial catastropic conditions favored small critters that could
get by eating almost anything, even tough dinosaur eggs.  Or malnourished
dinosaurs trying to babysit their eggs.

It's also vaguely possible that the dinosaurs adapted to the cold, but at
the price of losing the ability to adapt to the heat again.  We don't know
enough about dinosaur genetics to rule it out.  (At least, I don't.)

: >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?

Maybe they were allergic to the ragweed that grew so well in the cooler
climate.  I think every day I spend in these Santa Ana winds takes several
hours off my life.  (Beats having the smog though.)

If the chaoticists are to be believed, something much less dramatic
than an asteroid is capable much greater consequences than mere
extinction of dinosaurs.  Why, the flap of a butterfly's wing today may
influence whether the universe collapses next week...  well, perhaps
that's a wee bit exagerated...  Still and all, non-linear systems (and
we're not just talkin' weather) can behave oddly under seemingly mild
perturbations.  Let's remember that ecological niches aren't cast in
concrete, but at least partly in the flesh of whatever else wants to
occupy the neighboring niches, not to mention the same niche.  And
precedence matters--last one there is a rotten dinosaur egg!

: >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 :-).

It doesn't take much imagination to see that *something* changed to off
all the dinosaurs.  Just because we have difficulty imagining how the
bullet got from the smoking gun to the victim doesn't mean it didn't (or did).
To bend another saying to our use, we might say that "Absense of imagination
implies imagination of absence."  Just because I can't see the connection
doesn't mean there isn't one.  The "enormous problems" with a single
catastrophe are mostly problems in our head, because we ain't smart enough.
(Nothing personal, Keith.   :-)

I've got it now!  The asteroid hit an oil field situated over a fluorite
deposit sitting on a huge salt dome, and filled the atmosphere with
chlorofluorocarbons.  Anything that couldn't hide under a log and didn't
have fur or feathers had increased risk of skin cancer for the next
N thousand years.   :-)

Yes, unlikely.  But we don't know how many times Mother Nature tried before
she hit the jackpot.  Unlikeliness isn't a big problem in my book.

Go ahead, flame me, I've already reproduced.

Larry Wall
lwall@jpl-devvax.jpl.nasa.gov
"So many programs, so little time..."