Heat energy from the sun causes the liquid water to change into its gaseous form, water vapor, through evaporation happens constantly from lakes, rivers, oceans, etc. Water vapor enters the atmosphere in other ways.
(Water vapor; enters; the atmosphere) (Heat energy from the sun; causes; the liquid water to change into its gaseous form, water vapor)
Water vapor Heat energy from the sun
enters causes
the atmosphere
the liquid water to change into its gaseous form, water vapor