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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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In 1976 Robert Gentry published the results of a new round of research that drew unprecedented attention to the implications of his earlier work. He had long puzzled over the possibility of secondary polonium halos. If any existed, it seemed they would be found in a place where uranium was abundant, and in a substance whose internal structure would permit rapid infiltration and transport of a uranium-rich solution and which contained microscopic capture sites for polonium atoms to accumulate.

No material seemed more ideally suited to the special requirements of secondary halo formation than wood. Gentry was reminded of some specimens of radioactive wood he had heard of a few years earlier. A bit of sleuthing revealed that partially coalified pieces of wood, some as large as logs, had been found in several uranium mines in the western U.S. Gentry was finally able to obtain some samples of the wood and began studying them.

Microscopic examination of prepared specimens revealed an abundance of uranium halos in the wood. The evidence suggested that prior to coalification the wood had been in a water-softened condition, permitting the infiltration of water-borne uranium. Uranium atoms had accumulated in capture sites scattered through the wood and secondary halos had formed around the capture sites. Since enough uranium had been deposited in the wood to create halos, Gentry thought, perhaps there would be secondary polonium halos as well.

Gentry's hunch paid off. After painstaking examination, certain of the coalified wood samples revealed polonium halos in even greater numbers than uranium halos. Several unusual facts seemed to stand out, however. First, every polonium halo in the wood was from the isotope 210Po—not a single halo could be found from 214Po or 218Po. Suddenly it made sense. The 210Po isotope had a half-life of 138 days—long enough to be filtered out of the uranium solution and accumulate in the capture sites. The two other polonium isotopes, with half-lives of minutes or less, simply decayed away before they could accumulate in the capture sites.

This was a crucial discovery. Natural circumstances could hardly be more favorable for the formation of secondary halos than they were in the wood specimens. Uranium was abundant, and the porosity of wood afforded ideal opportunity for its infiltration. Even under such optimum conditions, however, only one halo type had been able to form. In contrast, all three halo types were profusely scattered through solid rock—where no significant amounts of uranium existed and where permeability was virtually nil. This was most compelling evidence that the halos in the rock could not be of secondary origin.

The second oddity was that most of the secondary polonium halos found in the wood were not perfectly round, but elliptical. This indicated that the halos were formed while the wood was still in a soft condition, before it was compressed by the weight of overlying sediment. After careful analysis it was found that the elliptical polonium halos in wood specimens taken from three different geological strata—Triassic, Jurassic and Eocene—were virtually identical. Evidence suggested that all the specimens had been infiltrated with the same uranium-bearing solution during a single event.

These findings had disturbing implications for conventional geochronology. The Triassic, Jurassic and Eocene formations are thought by most scientists to have been deposited tens of millions of years apart, but the elliptical halos showed that the wood specimens from each strata had been in a soft, porous condition, uncompressed by overlying sediment, and equally exposed to the elements at the time of infiltration. The simplest scenario to account for their infiltration would be a major flood which uprooted trees, soaking them in water which had absorbed large amounts of uranium from nearby ground deposits, and finally compressing them between layers of sediment. A flood like the one described in the biblical book of Genesis would have done just that.

During his investigation Gentry was puzzled to discover a small number of dual polonium halos in a few of the specimens. In these an elliptical halo was superimposed with a circular one, surrounding the same center. How did the dual halos form? The most likely cause, Gentry realized, was a second infiltration of a uranium-bearing solution occurring soon after the first, while the wood was still soft and porous. The centers of the polonium halos caused by the first infiltration would have an affinity for a uranium daughter, 210Pb, introduced in the second infiltration. This element decays with a half-life of 22 years to 210Po, which in turn would form a second halo.

If the wood remained intact for the duration, both halos would overlap perfectly and appear as one. If the wood were crushed or deformed after 22 years then the overlapping halos would be compressed into an elliptical shape together. But if deformation of the wood happened within just a few years of the second infiltration, then only the first halo, which had already formed, would be compressed. In 22 years the second halo would form a perfect circle around the flattened first halo.

Here was the answer to a question Gentry had not even asked yet: how much time had passed between the formation of the halos and compression of the wood? Geochronology based upon the uniformitarian principle, encompassing tens and even hundreds of millions of years, would be utterly confounded by the brevity of time suggested by the data at hand. The evidence was compelling that only a few years at most had elapsed between the first infiltration of the wood with uranium and the time when it was compressed by overlying sediment. Taken all together, the facts supported no other geological model as strongly as the Genesis flood account.

After amassing this large body of new data Gentry and several colleagues summarized their findings in a collaborative report published by Science.18 The published data showed a clear distinction between the secondary halo type found in coalified wood and the multiple, primordial halo types found in granite. In careful but unmistakable language the report questioned conventional geologic age dating as well as the uniformitarian interpretation of the entire geologic column. It was a challenge that seemed to demand a response from the scientific community.

18 Robert V. Gentry et al, 1976. "Radiohalos in Coalified Wood: New Evidence Relating to the Time of Uranium Introduction and Coalification." Science, vol. 194, p. 315.

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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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