We investigate the effects of focused electron-beam irradiation on exfoliated graphene on SiO2 substrates at energies of 1.5, 10 and 30 keV and dosage of 28.8 C/cm(2). Our objective is to understand the mechanism by which wide-area low-energy electron irradiation thins such samples. We test a previously reported mechanism in which the incident electrons produce defects in the graphene, pass through the graphene, and dissociate oxygen from the SiO2 underneath. The dissociated oxygen then reacts with graphene, etching it from below. We conclude that although oxygen may play a role in the etching, incident electrons at 1.5, 10 and 30 keV that pass through the graphene do not etch it. We propose wide-area irradiation may dissociate oxygen from the uncovered SiO2 substrate surrounding the graphene and produce etching from above.