Evolution of Terrestrial Atmospheres
All the terrestrial planets start off with
a substantial atmosphere. Mars lost most of it because of low escape speed.
Earth converted most of the carbon dioxide into rocks. Life may have kept Earth
warm
enough for liquid water during the “faint Sun” era through methane from
bacteria. Later, life produced free oxygen. Venus lost its water
because it stayed vapor due to the extra sunlight. Solar UV released
hydrogen, which escaped to space.