Robert Gentry has done a lot of research on some curious discolorations that appear in certain kinds of rocks (e.g. mica, in igneous granites). These discolorations are very small (a few micrometers) concentric circles. These kinds of "haloes" form around inclusions of radioactive material. As the radioactive elements decay, they give off alpha and beta particles, which fly into the surrounding rock. As they slow down by colliding with molecules of the rock, they do chemical damage to those chemicals. As they reach their slowest speed, they do the most damage. The chemical damage shows up as discolorations in the rocks.
Different radioactive elements give off different combinations of alpha or beta particles when they decay. Some elements decay by giving off an alpha or beta particle, converting the atom into a different atom that is still radioactive. This, then, decays by giving off another particle. Because different elements, or "nuclides" as they are called in this context, give off particles that have different energies, the "haloes" show up at different distances from the bit of radioactive material at the source.
Gentry's data are essentially these observations. (I mean no disrespect in summarizing the findings so briefly. I simply hope to keep this concise):
1. He finds haloes that have the several concentric rings (i.e. mulitple haloes) at distances from the center that would be expected for polonium decay.
2. He finds no evidence of uranium in these inclusions in the rock. This is important, because when U-238 decays, it produces polonium. Polonium isotopes have extremely short half-lives (seconds to minutes). The lack of uranium suggests that the polonium cannot be coming from this source.
3. He states, albeit with inadequate evidence, that the samples he has analyzed are from the "basement rocks" of Precambrian (or, he says, pre-Flood) age. The evidence is inadequate (my interpretation) because the samples were largely sent to him by others, without documentation of their site of origin.
Gentry interprets the data as follows.
The haloes are the decay signature of polonium. Therefore, these rocks contain polonium. However, there is no uranium to produce the polonium. Therefore, the polonium must have been trapped in the rock as it formed. Because polonium has such a short half-life, the rock must have formed very rapidly, otherwise the polonium would have decayed before the rock was sufficiently solid to trap it.
From this interpretation, Gentry concludes that the traditional geological explanation for the formation of granites must be in error. The traditional explanation is that molten rock cooled very slowly. If the rock did not cool slowly, but instead formed very rapidly, then one of the fundamental premises of the traditional geological theory is false. Since no geological theory accounts for such rapid rock formation, we must look for other explanations. Gentry concludes that the only logical explanation is sudden Creation.
Although Gentry's conclusion is at odds with current geological thought, it does follow the logical paradigm proposed by Sherlock Holmes: "when you have excluded the impossible, whatever remains, however improbable, must be the truth." Gentry suggests that the traditional geological explanation has been shown by his data to be impossible. Hence, what science would consider improbable--that a Creator exists--must be so.
There are those in the Creationist community who accept Gentry's logic, and believe that his findings are the death knell of evolution (cosmic evolution, earth evolution, and--if creation is the answer--biological evolution as well). Before we conclude that this is the case, we should look at the data more carefully. Has Gentry really ruled out natural mechanisms in the generation of these haloes, or are there plausible--even likely--explanations that he has overlooked?
We might address this by asking the following questions:
Gentry's model (hypothesis) is that polonium was trapped quickly during the formation of the rocks. What predictions does this model make?
1. Rocks of this type, and of this age, should be equally well sprinkled with polonium haloes, regardless of what other rocks are nearby.
2. Post-flood rocks should contain no such haloes, since they were not created at the instant of creation. (This includes granitic intrusions that have pushed sedimentary ("flood-deposited") rock up into mountain ranges.)
3. There should be no particular spatial relationship of polonium haloes to each other, or to other, more recent, features (such as cracks) of the rocks in which they are found.
4. There should be no particular "favoritism" for different polonium isotopes (Po-210, Po-211, Po-212, Po-214, Po-215, Po-216, Po-218). All should be found equally frequently, or in some logical relative-abundance series.
5. Of course, none of the above are predictions if we say that the Creator specifically chose the individual locations of each polonium halo, or of each set of discolored rings (with no polonium involved at all).
Alternative hypotheses, based on known scientific findings, must be ruled out. That is, to accept the improbable conclusion that Gentry suggests, we must show that plausible natural mechanisms are impossible. We should consider the following questions, some of which are based on the predictions of Gentry's hypothesis:
6. In what rocks besides those reported by Gentry have such haloes been found? In what rocks have such haloes not been found? (That is, if we look at the same kind of mica or fluorite, from various locations, do some deposits have haloes and some not?) Does the difference provide insights into natural factors that might be responsible for the haloes?
7. What radioactive isotopes produce the polonium isotopes that Gentry associates with these haloes? Uranium-238 is one; are there others? Can we rule these out as the origin of the polonium Gentry reports?
8. What, if any, polonium isotopes are not represented in the haloes?
9. What is the distribution of haloes in rocks in which they are found? Are they randomly distributed, or are they associated with particular physical features of the rocks?
10. A single polonium atom produces one decay, sending one particle into the rock in one direction. This does not produce a halo. It produces a dot. To produce a complete halo, it is necessary to have a very large number of atoms decaying, sending particles in all directions. Each halo is a collection of individual dots from many individual decays (thousands? millions? gazillions?). What natural source of polonium could exist in these rocks, in these locations, to produce a continuous supply of short-lived polonium atoms? (Gentry's model, apparently, proposes that the Creator put clusters of gazillions of polonium atoms into the rocks, not just single atoms. We cannot guess why He would do so. See point 5 above.)
11. Are such haloes found in rocks known to be of younger ages than the "primordial" rocks Gentry reports? That is, can they be found in rocks that are accepted as being younger than Precambrian (and therefore deposited during or after the Flood, according to Creationist geology)? Such rocks would include, as noted in 2 above, granitic intrusions that have pushed sedimentary rock up into mountain ranges.
12. On the basis of the answers to the above questions, what, if any, plausible natural explanation can we propose? If none, then we must consider Gentry's proposal seriously. If there is a plausible explanation that Gentry has not addressed, then we must set Gentry's explanation aside as "unlikely" until he or someone else has ruled out the plausible alternative explanations. (Of course, he should have done this before publishing his conclusions, but that's another matter.)
