I know that feeling ...
funny thing is, I can remember the time when I thought anyone
over 25 was a "living fossil" ...
>cough<
Quote:
Originally Posted by cran
have you considered other possible means to increase atmospheric pressure at sea level - or is oxygen the only factor?
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the reason I asked is that, while oxygen is vital for keeping our blood the right shade of red, etc, it's only one (and not the major) component of the atmosphere ... other bits of it have also shown signs of greater or lesser partial pressure at times ... and there are hints that the lower air column has also varied in height ... all of which suggests that 1 bar might not have always been the standard ...
The mention of 35% O2, and giant insects, rang a bell - is there some confusion here between the
Cretaceous ...
and the
Carboniferous?
Quote:
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Abstract Theoretical calculations, based on both the chemical and isotopic composition of sedimentary rocks, indicate that atmospheric O2 has varied appreciably over Phanerozoic time, with a notable excursion during the Permo-Carboniferous reaching levels as high as 35% O2. This agrees with measurements of the carbon isotopic composition of fossil plants together with experiments and calculations on the effect of O2 on photosynthetic carbon isotope fractionation. The principal cause of the excursion was the rise of large vascular land plants and the consequent increased global burial of organic matter. Higher levels of O2 are consistent with the presence of Permo-Carboniferous giant insects, and preliminary experiments indicate that insect body size can increase with elevated O2. Higher O2 also may have caused more extensive, possibly catastrophic, wildfires. To check this, realistic burning experiments are needed to examine the effects of elevated O2 on fire behavior.
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Abstract
Berner et al, 2003; Phanerozoic Atmospheric Oxygen; Annual Review of Earth and Planetary Sciences; Vol. 31: 105-134 (Volume publication date May 2003)