Correlation between surface heat flow and the radioactivity of surface rocks (RATE book, page 80) Robert Gentry claims to have found "squashed" polonium haloes as well as embryonic uranium radiohaloes in coal deposits from many geological layers claimed to be hundreds of millions of years old. (See the Oct. 15, 1976 issue of Science.)
Geologists have found a puzzling correlation between heat flow out of the ground, and the presence of radioative elements near the surface.  This should not be so if decay has proceeded slowly for millions of years.  A better explanation is that the pulse of heat from an interval of accelerated decay, has not entirely dissipated.