>>13245372Because it's hot. As I understand it, on Earth and Mars, silicate weathering causes absorption of CO2 from the atmosphere (or ocean) into mineral sinks as carbonates. At elevated temperatures, this process tends to reverse. This is why volcanic eruptions expel so much CO2, and also why the equilibrium between gaseous CO2 and carbonates in mineral sinks tends to favor the former on Venus. The result is a thicc atmosphere and high partial pressure of CO2.
Once the sun heats up enough to boil Earth's oceans, Earth will probably have the thiccest atmosphere in the hood.
>Please forgive and correct any errors in this post; I am just a popsci dweeb and not a planetary scientist 
