It varies. There is no single percentage value
3 to 4 percent
What happened to all the water vapour in the early atmosphere
I'm guessing water vapour
Yes, in the atmosphere water vapour falls as rain.
it becomes water vapour in the atmosphere.
ionosphere
Humidity is the amount of water vapour in the atmosphere
transpiration
Water vapour is a constituents in air because water vapour rises in the atmosphere & is always present in the atmospere in some or the other quantity.Also 0.0001% of air consist water vapour
0.082
As the earth cooled, water vapour in the atmosphere condensed to a liquid (water) and fell to the earth as rain the make the oceans.
The most variable abundance in the atmosphere is Water Vapour and Ozone