Explain Why does cool air sink and warm air rise in the atmosphere?

Cold air or cool air is more dense than hot/warm air, because of this. Warm air 'rises' and cold air 'sinks'. The cold air molecules are closer packed together than the warm air molecules. And the result of this is that warm air is less dense meaning also more apart which is why it rises.

Explanation:

for example, no new evidence will demonstrate that the earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the earth is not divided into solid plates that have moved over geological timescales .