Limits of anoxic ecosystems...
Hi Board
Another interesting piece from the Pale Blue Dot conferences...
http://astrobiology.arc.nasa.gov/palebluedot/abstracts/conrad.html
a detailed abstract, which describes the limitations of anoxic ecosystems. Without free oxygen the scale of the ecosystem is limited by supply of inorganic reductants - metals, sulphur etc. - for fixing CO2. Sunlight + water is whole lot more available than the other options.
Adam