Re: egg development and O-2

[Mike Taylor <mike@miketaylor.org.uk>]

> Date: Thu, 04 Aug 2005 06:03:28 -0600
> From: Ken.Carpenter@dmns.org
>
> [John Vanden Brooks] mentor, Robert A. Berner, the Alan M. Bateman
> Professor of Geology and Geophysics at Yale, characterized the range
> of atmospheric oxygen levels over multimillion year times scales,
> and established an upper value of about 31 percent oxygen, and a
> sharp decline near the Permo-Triassic boundary to about 12
> percent. Earth's current atmosphere is about 21 percent oxygen.

Ken (and others),

Any idea why people always talk about the _percentage_ of oxygen in
the atmosphere?  I'd have thought that the partial pressure would be
more important -- e.g. if the oxygen proportion fell from 20% to 15%
but the total atmospheric doubles, then, wouldn't the partial pressure
rise to 30% of the old total pressure (i.e. 1.5 times the old partial
pressure)?

Or is total atmospheric pressure constant because it's proportional to
g, or something?

Thanks.

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