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All of Earths gasses in the atmos:

Nitrogen (N2): approximately 78%
Oxygen (O2): approximately 21%
Argon (Ar): trace amounts (about 0.93%)
Carbon Dioxide (CO2): variable amounts, currently around 0.04%
Water Vapor (H2O): variable amounts, typically up to 4% in the atmos
Other gases: trace amounts, including neon (Ne), helium (He), methane (CH4), nitrous oxide (N2O), and ozone (O3)

All of these are created at ground level and rise upwards into the atmos due to buoyant force and the 2nd law of thermodynamics. The denser the gas, the lower the altitude. Each gas settles into it's equilibrium at varying altitudes and this causes a vertical density gradient.

Earth is the largest and densest object in the universe, objects seek their density equilibrium which is downwards, gasses seek their buoyance equilibrium, which is upwards.

Gas pressure is the force exerted by gas molecules colliding with the surfaces of objects.

The theory of gravity is not a surface nor an object. It is a needless theory that exists to invoke the belief of living on a ball.

To demonstrate gas pressure in any scientific experiment it requires containment, a physical barrier.

Never engage a Hasbara troll. Just point at them and lol or make fun of them.