Fig. 2. Simulated D/H evolution for different assumptions of crustal hydration and atmospheric escape rates.

(A to C) The evolution of the D/H of the exchangeable reservoir in our simulation. Most parameters, including X_ex,0, are fixed; R_ex,end is a free parameter to visualize the model sensitivity. The colored lines show results for different assumptions of the flux rates. The large range of D/H measurements from meteorite, rover, and telescope observations are indicated with gray rectangles (fig. S1). (A) Effects of increasing the Noachian escape flux (F_esc,N). (B) Effects of increasing the Hesperian escape flux (F_esc,H). (C) Effects of increasing the Noachian (F_crust,N) and Hesperian (F_crust,H) crustal hydration fluxes. When F_crust,N increases, the exchangeable reservoir becomes smaller, inducing larger fractionations during the Noachian. When F_crust,H increases, the allowed values of F_crust,N decrease, causing less fractionation during the Noachian.