Meditations on the ubiquity and mutability of nano-sized materials in the environment.

A wide variety of nanomaterials can be found naturally occurring in the environment, although finding and characterizing these materials remains a challenge due to their size. Recent studies in the field have shown that natural nanomaterials are common in many geochemical systems. In this issue of ACS Nano, Hutchison and co-workers make us realize that manmade nanomaterials can often be practically identical to those that spontaneously form in the environment. This Perspective discusses the prevalence of nanomaterials in nature, including anthropogenic and naturally occurring nanomaterials, and the dynamic behavior of these materials in the environment.