Mariner 10 OR and UV/OR ratio vs. approximate age of LRM deposits. Points and error bars are median deposit values and standard deviations reported in Table 3. Approximate ages for Degas and Akutagawa were set to the onsets of the Kuiperian and Mansurian periods as determined by M. E. Banks et al. (2017; 280 Ma and 1.7 Ga, respectively); Sholem Aleichem was set to 2.5 Ga (middle to early Calorian); Sobkou and Tolstoj basins were set to the ages determined by M. Le Feuvre & M. A. Wieczorek (2011; ∼3.8 Ga).