|Style over substance|
Radiohalos, pleochroic halos or, more specifically, polonium halos are minute, spherical areas of discolouration of minerals which are found in many igneous rocks. The discolouration is generally thought to be caused by alpha-particles released during the decay of radioactive elements held within the crystal structure, the size of the discoloured area being dependent on the initial isotope. However, as the size of some halos indicates that they have been caused by the decay of polonium (Po-218, which has a half-life of only 3 minutes) then the polonium could not have been trapped in the crystals as they formed by solidification from molten rock millions of years ago. Based on the work of young-Earth creationist Robert Gentry  this was claimed by creationists to be evidence for a recent creation. Gentry's theory was developed in the mid 1950s, prior to so-called "modern" computer science and modeling, and advanced technology.
"Robert Gentry's work showed that the Earth's granite was never in a molten condition, because polonium halos survive only in solid rock and the half-life of polonium is much too short to survive a multimillion-year cooling time. His results seem to indicate that the Earth was created instantaneously, in a cool condition. If true, it is clear evidence for creation and a young earth."
There are several arguments against this theory:
- Polonium is being created all the time as it is a decay product of the radioactive gas radon (which is itself a decay product of uranium). Radon is produced in large amounts in areas of granitic rock, sometimes in sufficent concentrations to present a serious health hazard. As radon is chemically inert, it can easily move through microscopic cracks in minerals and, at some point, it will decay into polonium. Thus there is no issue with pleochroic halos being found throughout a body of granitic rock.
- There is little evidence that the "halos" are, in fact, produced by polonium as opposed to other elements.
 External Links
- Robert Gentry's book, Creation's Tiny Mystery online
- See the Wikipedia article on Radiohalo.
- Polonium Halo FAQs at the Talk Origins Archive