C/O ratio over the disk in the gas phase and solid phase. The C/O ratio starts as a solar value in the gas phase, closer to the star. By condensation of Al₂O₃, at point 1, Mg₂SiO₄ at point 2, and KAlSi₃O₈ and NaAlSi₃ O₈ at point 3, the C/O ratio increases in the gas phase. Due to the lack of carbon in the solid phase for these steps, the C/O ratio is zero until point 4 where part of the carbon is condensed to form a meteorite-like composition. This results in a decrease in the C/O ratio in the gas phase. At point 5 the condensation of H₂O increases the C/O ratio in the gas phase. At point 6 CO₂ condenses into ice. This increases the C/O ratio in the gas phase up to 1. Finally at point 7, by condensing CO, the C/O ratio becomes solar in the solid phase. The gas phase at this point is oxygen and carbon free.