Andrew Yee wrote:
>Our Earth didn't start out with oxygen in
> the atmosphere. It probably contained methane and hydrogen, but no
This is in line with the evolutionary sequence in the development
of planets. Methane still dominates Titan's atmosphere and
methane is still degassing at Mt. Etna.
> Oxygen first appeared on the surface of the Earth when microbes
> developed the capacity to split water molecules to produce O2 using the
> Sun's energy.
Origin of oxygen should not be limited to microbes. Photolytic
splitting of water can also produce the free oxygen needed for
the formation of SiO2 or SO4 on Earth or Mars.