In the past, Mars had a ❌, which allowed for volcanism to take place on the planet. When ❌, they ❌ in the atmosphere, and ❌ the amount of CO2, a well-known greenhouse gas, making the atmosphere ❌. The greenhouse effect, in addition to a ❌ atmospheric pressure allowed for the surface temperature to be ❌, and for ❌ to be present on the surface.
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