Rate of water ice formation as a function of time at different radii beyond the snowline in the high-mass, high-viscosity CPD (7–10), to illustrate the two distinct stages of water ice formation. All values are normalized to the maximum formation rate at 10⁻⁵ yr, r = 0.08 R_H. The times where the decline in the abundance of free O and free H end are indicated by the gray vertical lines. The starting time t₀ is defined as when the infalling gas is shock-heated to an atomic and ionized state.