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.

Paul