"John Curtis" wrote in message
om...

Whether oxygen came from photosynthesis or photolysis, the ultimate
substrate was water. There is no free oxygen in space at
temperatures below 3300 K, nor is there any free oxygen in the
planetary interior as illustrated by deep sea volcanos:
http://www.pmel.noaa.gov/vents/chemi...ges/vents2.gif
Worthy of note is the absence of CO2 in the plumes of deep sea
volcanos, which lessens the likelyhood of photosynthesis.
I find no compelling reason to suspect that Mars deviated from the
composition of the solar nebula with a water to rock ratio of 2:1
http://www.genesismission.org/educat...lanetDiver.pdf
page 13. John Curtis

Thanks for that info. Is there a FAQ about atmospheric chemistry? I'm
reading this in
alt.sci.planetary. In photolysis, light breaks up water vapor into hydrogen
and free
oxygen, is that right? Does ultraviolet light do that or what? Does ozone
prevent it
from happening on earth?

rj