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Mystery in the Rocks

A physicist's discovery begins an extraordinary odyssey through
pride and prejudice in the scientific world.

By Dennis Crews

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Independent research is costly and difficult apart from the sophisticated laboratory facilities of a modern university, but Gentry was persevering. In a makeshift laboratory at home he began to study all the radiohalo specimens he could find, funding his research by working as a substitute high school math teacher. Patiently and meticulously he gathered data and catalogued the specimens according to type and quality.

Henderson had named the anomalous halo types he had observed A, B, C and D halos. Of all the halo types that had been documented, the ones that commanded Gentry's attention first were the ones most different from the others. The D halos were smaller than the others, with only a single fuzzy disc instead of a series of rings. Gentry split D specimens so that the halo centers were on the surface, then poured a special liquid photographic emulsion over the surface. When the emulsions were developed after a time and inspected microscopically, tiny alpha-emission trails were found radiating from the centers. This demonstrated that the centers were not extinct at all, but still radioactive.

Further research indicated that the D halos were simply uranium halos in early stages of development. It was a previously unknown but rather unsurprising bit of information, since the half-life of uranium-238 is calculated to be 4.5 billion years. Next Gentry turned his attention to the A, B and C halos. Henderson had believed these halos to be caused by alpha radioactivity from three isotopes of the element polonium, all members of the uranium decay chain. He theorized that some time in the past, water or some other solution containing uranium and its daughter elements must have flowed through tiny cracks in the rock and enough polonium had accumulated at certain points along the way to form halos. He had suggested that his hypothesis for this secondary mode of halo origins be tested, but World War II had intervened and the research was dropped.

Gentry's measurements confirmed that the rings were indeed produced by radioactivity from polonium isotopes. But the more he studied the specimens, the greater problems there seemed to be with Henderson's hypothesis for their origin. Close examination revealed many halos in solid areas that were free of any fissures or pathways by which radioactive atoms could have penetrated the rock. Further, there was no discoloration or any other typical evidence of uranium having flowed through the rock previously. Ultra-sensitive testing detected only minute traces of uranium in the surrounding rock—the same amount that existed throughout all mica specimens.

At last, all attempts to confirm Henderson's theory of a secondary origin for the polonium halos failed. Emulsion tests had shown the radioactivity of polonium halo centers to be extinct, which was expected from isotopes with such brief half-lives as polonium. For Henderson this had posed no great problem—but now that he had disproven Henderson's hypothesis, a profound new dilemma appeared. Polonium atoms decayed so rapidly there was no conventional way to account for their having existed in the rock at all.

The longest-lived polonium isotope, polonium-210, has a half-life of 138.4 days. Two beta-emitting elements precede polonium-210 in the decay chain, the longest lasting of which has a half-life of 22 years. If either of these parent elements were deposited in rock, the halo would begin to form as soon as the beta-emitting parents had decayed into polonium, an alpha-emitter. Polonium-214, which has a half-life of 164 microseconds, is preceded by two beta-emitters with respective half-lives of only 27 and 20 minutes. And polonium-218 has a half-life of just three minutes—with no beta progenitor at all. Thus polonium-218 would have to be deposited inside solid rock the same moment it came into existence, in order to form a halo. Now he clearly saw why Henderson had suggested a secondary mode of origin for polonium halos.

To find radiohalos in granite caused by such short-lived isotopes as polonium was an utter scientific paradox, he realized. Why? Radiohalos can form only in solid rock. Much of the granite encasing the polonium halos was Precambrian, which is believed by most scientists to have taken millions of years to cool from its molten state. Since so few of the rocks which encased the halos had clefts or passages by which polonium atoms could have entered, the polonium had to have existed from the very formation of the rock itself. Yet polonium isotopes have an extremely fleeting existence, and would decay away long before even a small chunk of molten granite could cool and solidify. Was this the kind of discovery the head of the physics department had feared he would make?

All the evidence indicated that the polonium had originated concurrently with the formation of the granite itself. Yet if it had, according to conventional science it quickly would have decayed away, and in the molten primordial mass its telltale halos never would have formed. Was it irresponsible to consider that the tiny radiohalos—a minor, overlooked mystery for so many decades—might be evidence of instantaneous creation locked into the earth's crust? And of crucial importance—was it possible that he had overlooked something that could provide a more conventional explanation for the halos?

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For readers interested in a more comprehensive treatment of this story, Robert Gentry's book, Creation's Tiny Mystery, is available for $18 (U.S.) + S/H.

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The above page was found at on April 21, 2014.

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