The mean speeds are greater than the escape velocity from the Earth. Most of the H and He escaped long ago. The energy received from sunlight Blackbody energy radiated by the warm Earth. The ground absorbs sunlight Absorbs UV, visible, and IR photons. Greenhouse Effect Atmosphere is transparent to visible light, but mostly opaque to infrared.
Sunlight heats the ground, warming it up.
Without the greenhouse effect, there would be no liquid water on the Earth, only ice, and consequently there would be no life. Radiative trapping does contribute, but only to a fraction of the heating experienced inside a greenhouse. Atmospheric Pressure Weight of air above makes the surface pressure higher. A key feature of an atmosphere is how its temperature changes with altitude. H 2 O condensed to form the oceans.