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Re: "Oxygen Helped Mammals Grow, Study Finds"



Don,
That's useful info!
And to correct a misstatement I made earlier:  The graph would involve
altitude vs. partial pressure of O2.  I mistakenly typed % O2.

<pb>
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On Fri, 30 Sep 2005 12:12:56 -0700 (PDT) don ohmes <d_ohmes@yahoo.com>
writes:
> If memory serves--
> The relation o2/air is effectively constant over
> biospheric altitude; 10% o2 at sea level = ~10% o2 at
> 3km. Assuming standard atm mass of 5.14 x 10^21 gm (an
> unsafe assumption, IMO) ppo2 will track the graph of
> mb air/altitude; not linear but easily found in most
> meteorological texts. 
> 
> 10% o2 seems VERY low to me.
> 
> Don
> 
> --- Phil Bigelow <bigelowp@juno.com> wrote:
> 
> > 
> > 
> > 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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