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Re: "Oxygen Helped Mammals Grow, Study Finds"

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.

If anaerobic bacteria became more abundant because of a much lower
atmospheric O2 %, then there would be an parallel increase in the out
gassing of methane from the Mesozoic soils.  Methane is the strongest
greenhouse gas.  Hmmm......

Indeed! :-)

Besides, Falkowski et. al's conclusion is the polar opposite of some
conclusions from a few years ago!  Didn't  J. Keith Rigby Jr. et. al,
among other teams, claim that O2 levels were much *greater*
during the Mesozoic?

Yes, but (according to Nature News) that was based on a lot less data.

Reptiles in what sense?

See why I hate that term so much! :-)

And isn't a T. rex a "large animal"?

Sure, but it didn't have the placental mode of reproduction. Viviparous animals are expected to have the greatest need for high oxygen levels -- the fetus needs to extract oxygen from the mother's blood, and if the mother already has trouble extracting oxygen from the air...

- If O2 % starts to fall (probably at the cost of increasing the CO2
level), the oceans' photosynthetic organisms will proliferate, gobbling
up the excess CO2 and pooping out O2, thereby reestablishing the O2
percentage to its former level.

Not when, say, iron is missing in the seawater.

Today the biggest component of marine phytoplankton are the diatoms. One of the reasons is that the silicon dioxide they need to build their shells is provided aplenty by -- grass. Grass phytoliths are more easily soluble in water than, say, granite. It has been shown that diatoms and grasses had a parallel increase in abundance.

- If O2 % starts to become too abundant (probably at the cost of
decreasing CO2), an increase in the number and intensity of wild fires
and other oxidation processes occurs, which decreases the O2 and
increases the CO2.

Hard to avoid.