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Re: Atmosphere at K-T extinctions




"James R. Cunningham" wrote:
> 
> Joe, would you like for me to scan and send you a JPEG of Dudley's graphs of
> atmospheric oxygen and CO2 contents from the Cambrian up through the present?


Actually, your reply below is the kind of information I've been seeking. The 
impact and the Deccan traps are generally accepted; the changes in atmospheric 
content are apparently subject to some ambiguity.

I recently read "Stepping Stones" by Stephen Drury (a Natural Science Book 
Club monthly selection) and his descriptions of earth history are strong on 
the effect environmental changes have on the extant life forms of any period. 
Some of these changes he attributes to the end result of the life forms' 
activities in supplying elements/compounds to the atmosphere and the sea.

This book is at the level where an interested layman can comprehend the 
discussions. My questions about the K-T atmospheric changes were due in part 
to having recently read the book. If oxygen concentration went up, something(s) 
else decreased. The mix was before and after the extinctions, how that may 
have affected/been affected by the seas and the flora, and the potential to 
disrupt the food chain were part of the "jigsaw puzzle" I mentioned.

I can understand how atmosphere trapped in amber relates information about the 
prehistoric conditions. What are some other techniques used to measure gas 
concentrations? Does any of the "endotherm/ectotherm/something else" debate 
address evidence of physiologies suited to certain atmospheric conditions based 
on fossil evidence from dinosaurs (or from contemporary creatures)?

Thanks for your help and your patience,

 Joe

> I think the difference in his paper and Hedge's work may indicate that there 
> is
> still some uncertainty about the oxygen spike at the end of the Cretaceous.  I
> personally don't have a clue who of the two is correct, but think the amber 
> tests
> may be pushing the limits of technology and statistics.
> 
> Incidentally, I looked the paper up (Atmospheric Oxygen, Giant Paleozoic 
> Insects
> and the Evolution of Aerial Locomotor Performance, R. Dudley, JExB), and 
> Dudley
> shows a high of about 35% just before the beginning of the Permian, with a 
> rapid
> decline to a low of about 13-14% near the beginning of the Triassic, then a 
> small
> spike at about 17% in mid Triassic, another drop to about 14-15% early in the
> Jurassic, a sudden climb to about 21% by mid-Jurassic, then a gentle climb to
> about 26% early in the Tertiary, and a rather constant, steaty decline to the
> present 20.9%.  Please note that my memory failed me about the timing of the
> latest oxygen decline (I was thinking about the CO2 curve which peaked at 
> about
> the first third of the Cretaceous, and has since declined steadily till 
> recently),
> but I was correct about Dudley's lack of an oxygen spike near the end of the
> Cretaceous.
> 
> Seosamh wrote:
> 
> > In the thread on theories of extinction causes the discussion
> > of atmospheric change came up. I'm unclear on what the changes
> > were.
> 
> So is everyone else, I think.
> 
> > I do realize that the general trend in oxygen levels has been
> > toward lower concentrations since before the Mesozoic.
> 
> Per Dudley, there was a steady climb from a low near 15% about 200M years ago 
> to
> about 26% 50M years ago.  I don't know if he was correct, but think he may 
> have
> based his work rather heavily on that of J.M. Robinson.  He also cites Watson,
> Kump, Berner, Canfield, Makowski, Wignall, Twitchett, Hart, Holland, and 
> Isozaki.
> 
> > Tony Hedges
> > pointed out that there was a sudden spike in the oxygen
> > concentration at the end of the Cretaceous:
> 
> Dudley doesn't show this, apparently based on Berner And Canfield.
> 
> > > 3. Atmosphere.
> > > Studies of the atmospheric content contained within amber dated to the end
> > > of the Cretacious period has shown that towards the end of the last period
> > > of the dinosaurs reign contained a smaller ammount of Oxygen in the mix,
> 
> Dudley - larger
> 
> > and
> > > towards the end of the Cretacious the Oxygen content shot up by some 20 -
> > > 23%. This is a significant increase.
> 
> Dudley - slow steady increase of about 25% from mid-Cretaceous to early 
> Tertiary.
> 
> Cheers,
> 
> Jim