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Re: "Oxygen Helped Mammals Grow, Study Finds"




On Fri, 30 Sep 2005 08:56:44 -0400 Jeff Hecht <jeff@jeffhecht.com>
writes:

> >Here's another interesting corrolary.  I wonder if the authors 
> considered
> >it as they were preparing their manuscript:
> >
> >If the 10% O2 figure is correct (for SEA LEVEL), then the anoxic 
> altitude
> >would have been vastly lower than it is today.  Meaning that even
> >moderate elevation mountains in the early Jurassic may have been 
> totally
> >devoid of all animal life. (We REALLY need an O2 vs. altitude graph 
> for
> >the early Jurassic, using as a starting point a 10% O2 
> concentration at
> >sea level (1 atm).  Is anyone up to the task?).


> Marine oxygen levels also depend on atmospheric concentrations, so 
> some effect should be visible in the ocean. Given the nature of the 
> fossil record, that would be easier to see than the effect at high 
> elevations. 


True, and I'm currently not addressing the issue of whether their
conclusions are accurate.  Let's assume that they are accurate.

But the construction of a new O2 vs. elevation graph for the E. Jurassic
would need to rely only on one datum point (the hypothetical 10% figure).
 The rest of the procedure is just finding the mathematical relationship
between ppO2 and height (which is probably well known).  This is one rare
instance where empirical data is unnecessary.  We should be able to rely
solely on known atmospheric chemistry principles.

I know nuthin' 'bout birthin' no graph.  But let's assume that the
relationship is linear and that the slope of the line is known and it is
the same as it is today,  then it is only a matter of using the new
starting point (Y-intercept), which in this case is 10% O2.  The graph
for the early Jurassic atmosphere might therefore look like the graph for
our present atmosphere, but with the line just shifted down towards the
X-axis.

Hmmmm.....I may have to look into this further.  I best be commencin' to
do some book learnin'.



<pb>
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