Atmospheric CO₂ of an abiotic planet (left column), a biotic planet (centre column), and the difference between the two (right column). We tested different oxygen fugacities ${\text{f}}_{{\text{O}}_2}$ (a–f), initial mantle temperatures T₀ (g–l), and reference mantle viscosities η_ref (g–l) keeping the respective other parameters equal to the baseline model (${\text{f}}_{{\text{O}}_2}=\text{IW\hspace{0.17em}-}0.2$, T₀ = 1900 K, η_ref = 10²¹ Pa s).