Disc evolution for different disc configurations. Top: viscous disc without internal photoevaporation. Middle: viscous disc with internal photoevaporation due to X-rays. Bottom: viscous disc without internal photoevaporation where a planet seed is put at 3 AU at 0.05 Myr. The planet has a final mass of about 2860 M_Earth, and reaches pebble isolation mass at 0.1 Myr. Left: gas surface density as a function of disc radius, time evolution is shown in colour – from black, which corresponds to 0 Myr, to dark red, which corresponds to 10 Myr. Right: gaseous C/O ratio as a function of disc radius and time (colour-coded). The evaporation lines for different molecules are given as grey dashed lines. Note that the C/O ratio is calculated from number densities scaled to the solar value and that we, by definition, have no specified C/O ratio in the gas phase beyond the CO evaporation front. We use our standard parameters for this simulation, as given in Table 4.