Answer:
Heat leaves the Earth primarily (as others have mentioned) as various forms of EM radiation, and also with a small amount by “evaporation”. The smallest atoms in the upper atmosphere can gain enough energy from a collision with a larger one that their speed exceeds the escape velocity.
Explanation:
1. radiation into outer space. This occurs on cloudless nights.
2. radiation into the atmosphere
3. conduction into the atmosphere, which eventually radiates into outer space
4. convection into the atmosphere, which is a form of conduction, eventually radiates into outer space
