Escape parameter Φ_i as a function of time for our Mars analogue. We show results both for our standard assumption that molecules are dissociated into O, C, and N in the thermosphere (full lines) as well as for an alternative model where the molecules are assumed to remain intact (dash-dotted lines). We bundle CO and N₂ together in the plot, due to their similarity in both binary diffusion coefficient (Zahnle & Kasting 1986) and molecular weight; this gives a similar escape parameter. The escape flux of hydrogen is in all cases high enough to drag along all heavier species (Φ_i ≫ 1) until all the hydrogen has been depleted.