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Polonium Halos: An Independent Evaluation
Professor Feather's interest in polonium halos was apparently traceable to some of my publications. He understood that the 210Po halos discovered in coalified wood were secondarily derived from uranium activity. At the [p. 70] same time, he also saw that the origin of the different types of polonium halos in granites raised some difficult questions. His theoretical investigation, entitled "The Unsolved Problem of the Po-Haloes in Precambrian Biotite and Other Old Minerals," was published in 1978 in the Communications of the Royal Society of Edinburgh (Feather 1978). His conclusions are aptly stated in the Synopsis of his article:
Ever since the discovery of Po-haloes in old mica (Henderson and Sparks 1939) the problem of their origin has remained essentially unsolved. Two suggestions have been made (Henderson 1939; Gentry et al. 1973), but neither carries immediate conviction. These suggestions are examined critically and in detail, and the difficulties attaching to the acceptance of either are identified. Because these two suggestions appear to exhaust the logical possibilities of explanation, it is tempting to admit that one of them must be basically correct, but whoever would make this admission must be fortified by credulity of a high order. (Feather 1978, 147)
Feather's doubts about polonium halos in granitic micas having originated from uranium daughter radioactivity, or from isomers, in essence confirm my earlier investigations. His conclusions were derived from a theoretical investigation of the nuclear properties of the relevant isotopes. My 1968 and 1976 Science reports (Gentry 1968; Gentry et al. 1976a; Appendix) and the 1973 Nature report (Gentry et al. 1973), to which Feather refers, show respectively that the secondary radioactivity and isomer hypotheses are not valid for polonium halos in granites. Feather did not propose a primordial origin of the Po halos as I have done, yet the results of his investigation greatly strengthened my contention that a conventional explanation of the Po halos in granites is scientifically untenable.
York did not mention this information in his review in EOS. I felt it necessary, then, to comment on Feather's work in my rebuttal, finally published on July 1, 1980, almost one year after York's article had appeared. It is quoted in part below:
York seems to regard even the existence of Po halos as only tentative. But notwithstanding the uncertainties, his article leans heavily toward the proposition that Po halos do exist, at least in micas. York's thesis is that Po halos are most probably explainable within the accepted framework because the interlocking nature of various radiometric dating techniques provides powerful evidence that conventional geochronology is correct. York faults me for ignoring this internal consistency. Contrary to his understanding, I do not ignore these data. But neither do I accept the idea that the presumed agreement between techniques is really coercive [p. 71] evidence for the correctness of the uniformitarian assumption which undergirds the present model. There was no discussion of the 238U/206Pb ratios [Gentry et al., 1976a], which raise significant questions about the accepted geochronological scheme.
While I can appreciate York's desire to emphasize internal consistency, it should be evident that irrespective of how much data has been or yet can be fitted into the present model, the question of its ultimate reliability hinges on whether there exist any observations which falsify the theory. . . .
York's surprise that I would accept Henderson's hypothesis for Po halos in coalified wood [Gentry et al., 1976a] but reject this explanation for mica because of the slowness of solid state diffusion suggests first that the same type of Po halos has been found in both substances and second that my only objection to accepting Henderson's hypothesis in mica was the slowness of solid state diffusion. Here some very important data have been glossed over.
Mica contains three types of Po halos, but coalified wood only one. Much evidence suggests the 210Po halos in coalified wood formed from selective accumulation of 210Po and 210Pb, which have half-lives sufficiently long (138 days and 22 years, respectively) to have migrated to the radiocenters before serious loss occurred from decay. Likewise, the relatively short half-lives of 214Pb and 218Po (27 minutes and 3 minutes, respectively) mean these nuclides generally decayed away before reaching the accumulation sites, which explains the absence of 214Po and 218Po halos. Thus the crucial question is: If Henderson's model results in only 210Po halos being formed under ideal conditions of rapid transport (plus an abundant supply) of U-derived Po atoms, then how can this model account for all three Po halo types in mica, where both the U content and the transport rate are considerably lower? Indeed, the close proximity in clear mica (i.e., without any conduits) of two or more types of Po halos presents what may be incontrovertible evidence against explaining these halos by Henderson's hypothesis [Feather, 1978].
Finally, York failed to mention that my hypothesis that Po halos in Precambrian granites are primordial [Gentry, 1974] could in theory be falsified (and Feather's objections negated) by the experimental synthesis of a biotite crystal that contained at least two dissimilar Po halos in close proximity [Gentry, 1979]. (Gentry 1980, 514)
The publication of this response showed that Dr. Spilhaus was determined to abide by the principles enunciated in The Affirmation of Freedom of Inquiry and Expression (see Overview). This was the second time that scientists had been challenged to produce the experimental results that would [p. 72] substantiate the evolutionary view of earth history, and at the same time, in theory, falsify my evidence for creation. I wondered whether there would now be a response, or whether the challenge would continue to be ignored.
Only time would tell.
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