The original post: /r/askscience by /u/OctupleCompressedCAT on 2025-02-19 20:11:43.

Between hothouse and ice age periods the difference in overall temperature should change how much water vapor is in the atmosphere over all. Would that effect be significant on the total pressure?

What about over longer periods? Is the amount of nitrogen fixed since the earth formed? Since the oxygen level varies, was the pressure up 25% during the carboniferous? What about before oxygen was present? Would CO2 and methane take up a similar amount to what oxygen does today or was it mostly nitrogen?