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Re: K/T Extinctions. Volcanic-Greenhouse or Impact?
> > Due to the incident 47% of the genera on the planet
> > packed their bags and quitely became extinct, taking with them 76% of
> > the species around at the time Including 96% of all marine species.
> > This mass extinction also removed 90% of the marine calcareous
> > nannoplankton which probably had an influence on the outcome of the
> > event, and will be discussed in the conclusion of this essay.
> The _Permian_ extinction killed off 96% of marine species, but the
> K-T extinction was not nearly so destructive. David Raup
> ("Extinction: Bad Genes or Bad Luck?") says that the loss rate was
> about 38% for marine genera, a bit higher for land animals, and
> land plants don't seem to have been nearly as
> badly affected. .
On this count, I was relying on the information of a Dr JE Marshall
from the geology department of Southampton University. I shall
question him up on this fact.
> Regarding the iridium anomaly, one of the major indicators of an
> impact, not volcanic, origin for the iridium is that the iridium
> isotopic ratio does not match Earthly iridium, even volcanic
> iridium. However, it does match closely with the isotopic ratio for
> iridium found in iron and stony-iron meteorites. This is something
> that an awful lot of people seem to forget about, but it's a
> critical point because it all but rules out a terrestrial origin
> for the iridium anomaly.
The reference for a combined theory seemed to indicate that the
iridium isotropic ratio of some samples (the minority I admit) did
match the Earthly iridium, while the majority did not. The essay only
discussed the theories, excluding the conclusion, and regurgitated
views made by others. As I said in the conclusion many scientists
(Present company excluded of course :¬) ) will find the most relevant
information to them and discard others somehow. I admit, I'm probably
doing the same on many counts. Still, please not that I have
concluded by agreeing myself with the combined theory. I think that
volcanic activity had been reducing populations on many species
causing the 'stepped' extinctions seen, with the impact being the
final kick in the butt.
> CO2 is not that efficient a toxin. Old-time submariners during
> World War 2 proved the hard way that humans can live, at least
> temporarily, in an atmosphere with as much as one or two percent
I think the key word here is 'temporarily', the old time mariners
changed their air as often as the could, and even then you've got to
remember that physical activity was fairly low, with what activity
there was usually resulting in them blowing up the enemy (hence they
can go change their air) or getting blown up (no need to change the
air!) Now try and imagine the effect it would have on animals who
suffer prolonged exposure. My guess is that herbivores might not
suffer greatly, their food would be flourishing and it tends to sit
still for them, but for carnivors, I expect running around trying to
hunt in a high CO2 atmosphere would have caused extreme exhaustion
problems. It can probably be easily modelled by those who know how.