This interpretation of the previous results, as well as results presented below, relies on extensive literature on oxidation of various forms of carbon, particularly graphite, some of which is discussed in the SI. Briefly, etching is O2 dissociative adsorption, followed by CO/CO2 desorption, and the decrease at higher TNP has been attributed to competition from O-atom desorption. Surface chemistry studies have shown that perfect graphite basal planes have near-zero reactivity towards O2 in this temperature range, but etching is observed at sputter-induced basal plane defects and at prismatic surfaces, which expose basal plane edges. For example, Olander et al. observed etching at sputtered basal plane defects from 1400 -1500 K at O2 fluxes of ~100 O2 collision/sec/nm 2 , about 30% lower than our flux. Etching at defects tends to expand the defects laterally, leading to 2D etch pit formation. For example, Edel et al. studied pit formation during HOPG etching to peak at 1200 -1400 K, using O2 fluxes of ~0.1 O2 collisions/sec/nm 2 . It is interesting to note that the TNP range where we observe the maximum etching rates is similar to the range seen in the surface chemistry experiments, but also in experiments with bulk graphite at much higher pressures. For example, Wall et al. observed the steady state etching rates for bulk graphite to peak between 1700 -1900 K, and Rosner et al. observed peaks in the 1500 to 1750 K range, with O2 partial pressures in the Torr range, compared to the ~4 x 10 -5 Torr pressures typical of our experiments.