Radiohalos provide a direct comparison of the results of identical physical processes that occurred over a period encompassing a large fraction of Earth's history. Accordingly they can demonstrate changes in natural process rates, i.e., in basic physical law, that occur too slowly to be demonstrated by observations made during the epoch of modem science, or that occurred episodically before the development of modern investigative capability. The identifiability of radiohalo rings with the alpha-particle sources that produced them together with the sharpness of these rings indicate that radioisotope half-lives over a range of 21 orders of magnitude have not varied by more than a factor of two during the time the geological formations of the Earth which contain radiohalos have been in existence, and probably over the entire time represented by geological formations. A plausible further deduction from this evidence is that there has been no significant variation in the nuclear long-range force, the nuclear short-range force, or the electrical interaction force during this time interval.