Air on earth is densest at sea level, or the lowest portions, as the heavier contents sink, naturally, w/ very low pressure the higher up we go. If we observe, for instance, a canister of propane, we feel the liquid at the bottom, w/ the upper region’s gas pushing against the inner surface, w/ intensity depending on pressure, volume, & temperature (according to Newton’s Ideal gas law). If we puncture or create a release, the gas will escape, equalizing to its nearby space. If conditions are just right, the pressurized canister can explode or collapse, common enough phenomena. Extrapolating, our breathing air would quickly escape to space if the system were open, insinuating a firmament or barrier.
Note w/ canning, cooking times differ depending on altitude, as boiling temperatures decrease the higher up you go, & different pressures are needed to achieve the same result (food safety guides confirm this).
