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Re: "Oxygen Helped Mammals Grow, Study Finds"



If you want to consider the impact on archosaurs of the supposed oxygen levels, 
you really need to look at the plot in Figure 2 of the Science paper. 

The paper claims that oxygen concentration was at 10% only at the start of the 
Jurassic, and by implication in the Triassic, although the paper does not plot 
oxygen levels before the Jurassic. (The curve is based on Bob Berner's work, 
but I think it's calculated freshly in this paper using some new data.) They 
show oxygen level rising to about 17% in the early Jurassic, then dropping down 
to 12% and rising to 19% at the end of the middle Jurassic. From the start of 
the cretaceous through until the early Eocene, oxygen levels range from 15% to 
18% or so. 

As a calibration point, air pressure at an altitude of 5 kilometers is about 
half that at sea level, so air at that altitude has about as much oxygen as 
sea-level air would have at 10% oxygen concentration. 

At 11:49 PM +0200 9/29/05, David Marjanovic wrote:
>> 10%??  Oh come on....
>> Has anyone even bothered to TEST this hypothesis?  Construct an
>> atmospheric testing chamber with 10% O2 and record the activity level of
>> a gecko, a baby alligator, and a canary (one at a time).  Can they thrive
>> and live long enough to reproduce?
>
>I don't know about geckos, but the lungs of crocodiles look like they've been 
>actively downtuned. (Same for goannas.) The canary would certainly survive, 
>though it might not be able to fly anymore...
>
>Humans are said to need 13 %. 10 % does sound extreme.
>
[clipped]
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Jeff Hecht, science & technology writer
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