Pressure as a function of temperature for our Earth analogue at three selected times. Before the dissipation of the protoplanetary disc, at t = 4.0 Myr and t = 5.0 Myr, the atmosphere connects to the envelope at a pressure and temperature that increases with time as the hydrostatic envelope becomes more massive. The removal of the gas envelope after disc dissipation at t = 5.0 Myr leads to a much lower pressure and temperature at the photosphere of the isolated planet. The partial pressure of water vapour (thin blue line) follows the shape of the atmospheric pressure for high temperatures (translated down in pressure to reflect the water vapour mixing ratio) and the saturated pressure (dotted blue line) for low temperatures.