Greenhouse gases (e.g CO2) are much heavier than air so how do they trap radiation in the upper atmosphere?

Question

Supposedly green house gases trap radiation and prevent it from leaving the earth into outer space. But these gases are heavier than air, they should be close to the earth's surface, how are they in the upper atmosphere and acting as a "blanket"?

Answer 1

Gases spread through diffusion. The fact that CO2 molecules are heavier than those of N2 and O2 only means that they become denser when you get closer to the surface.

Moreover, CO2 in the lower atmosphere is removed by plants and algae for photosynthesis and replaced by O2. This tends to lower the concentration of CO2 near the surface of the Earth.

Answer 2

Turbulence and diffusion are more relevant in atmospheric chemistry than stratification by density.