Using atomic force microscopy and Raman spectroscopy, we characterize the highly disordered morphology of single-layer and multilayer graphene sheets that results from long exposures to ozone molecules and oxygen radicals in an ozone generator. We identify a crossover from a nanocrystalline phase to an amorphous carbon phase in single-layer graphene as the exposure time is increased. We then consider the nanocrystalline phase and compare the morphology of single-layer sheets, multilayer sheets, and graphite flakes. Finally, we find that salient structures, such as steps and folds, act as sinks for disorder. © 2011 American Chemical Society.