Ok, well assuming they had similar humidities,two similar air masses would just simply mix with no sensible effects caused by the mixing...
Explanation:
Cenozoic = 100 mil years (rounded) = 66 real
Mesozoic = 200 mil years (rounded) = 174 real
Paleozoic = 300 mil years (rounded) = 330 real
Cenozoic = 100mil/4.6bil = .0217 (x100 for percentage) = 2%
Mesozoic = 200mil/4.6bil = .0435 (x100 for percentage) = 4%
Paleozoic = 300mil/4.6bil = .0652 (x100 for percentage) = 7%
Gravity and rainfall are major causes