XPost: sci.geo.geology, alt.sci.planetary   
   From: g_d_pusch_remove_underscores@xnet.com   
   Copy: dietz@dls.net   
      
   "Paul F. Dietz"  writes:   
      
   > Gordon D. Pusch wrote:   
   >   
   >> If Earth-life hadn't happened to accidentally stumble across the trick   
   >> of spewing out the nasty toxic poison waste-product gas called "oxygen,"   
   >> Earth's atmosphere would still have even _MORE_ CO2 in it than Mars's ---   
   >   
   > Why?  Most of Earth's carbon is fixed in carbonates, not organic materials,   
   > right?  The presence of large amounts of liquid water on Earth causes CO2 to   
   > react more quickly with positive ions from weathered silicates.   
      
   Yes, but that reaction had already proceeded to equilibrium before life   
   evolved.   
      
   Remember that the carbon in carbonate rock is constantly being recycled   
   back into the atmosphere by volcanic activity, and that essentially all the   
   O2 in the atmosphere is the result of chlorophyll-based photosynthetic life,   
   constantly replacing one molecule of atmospheric CO2 with a molecule of O2.   
   Without chlorophyll-based photosynthetic life, there would be essentially   
   no free O2 in the atmosphere, and instead there would be the same order   
   of magnitude number of CO2 molecules (modulo concentration shifts in the   
   atmosphere/ocean CO2 equilibrium point).   
      
      
   -- Gordon D. Pusch   
      
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