[DB 1507 (24); OAB 70] Radiohalos are a well-known geological phenomenon. They are small disruptions of a mineral's crystal structure caused by the radioactive decay of an element in the crystal. The identity of the decaying element can often be determined because the energy released by the decay depends on what the element is. The claims of Dr. Robert Gentry, detailed in his book Creation's Tiny Mystery (Knoxville, TN, 37912-0067: Earth-Science Associates, 1986), concern certain isotopes of the element polonium, which are short-lived decay products of uranium-238. Gentry claims that certain rock samples contain polonium radiohalos but are missing any radiohalos from the "parent" element, uranium. Gentry's conclusion from his observation is that the rocks in question were created instantaneously, with the polonium already in place, thus explaining why no evidence of the "parent" uranium is present. Because of the short half-lives of the polonium isotopes (Po-218 has a half-life of 3 minutes), Gentry claims that this is the only way to bring the polonium into the crystal, while the crystal is solidified enough to preserve the radiohalo, before the polonium decays away. While it is true that these radiohalos are not fully understood by scientists, this does not mean that Gentry's hypothesis should automatically be accepted. Other scientists have contended that there are other possible explanations for the radiohalos, including a process called hole diffusion (see A.L. Odom and W.J. Rink, Science, v.246, pp.107-109 (Oct 1989)). A summary of evidence against Gentry's hypothesis was written by Kurt Wise, who doubts the validity of Gentry's methods even though Wise is himself a young-Earth advocate (K.P. Wise, Creation Research Society Quarterly, v.25, pp.171-176 (1989)). The death blow to Gentry's hypothesis is given by the geological setting in which his samples were found. A geologist named Jeffrey Wakefield, while investigating Gentry's claims, determined that some of his samples were not from primordial rocks at all, but from younger dikes (infusions of igneous rock into pre-existing rock) that crosscut older formations (see J.R. Wakefield, Journal of Geological Education, v.36, pp.161-175 (1988), orhttp://www.csun.edu/~vcgeo005/gentry/tiny.htm). A recent article defending Gentry (ICR Impact #326, http://www.icr.org/pubs/imp/imp-326.htm) conceded that some of the radiohalos are indeed found in younger rocks, feebly countering that not all of his samples are in that situation. However, that is beside the point, because if any of Gentry's radiohalos occur in samples that everyone agrees (even young-Earth advocates) were formed by natural chemical processes, then there must exist a natural chemical process by which the halos are formed. Polonium-218 halos are simply an Unexplained Mystery. It is true that we do not fully understand the chemical process that formed them, but we can safely adopt the working hypothesis that that process was natural rather than supernatural.