Hi Perry,
One of the most powerful quotes in the book Life How Did It Get Here? - By Evolution or Creation was this one from Robert Gentry:
Before concluding that Bible chronology is in error, consider that radioactive dating methods have come under sharp criticism by some scientists. A scientific journal reported on studies showing that "dates determined by radioactive decay may be off -- not only by a few years, but by orders of magnitude." It said: "Man, instead of having walked the earth for 3.6 million years, may have been around for only a few thousand.
You can see this on page 96. This one quote, for many years, made me suspicious of such so-called "radioactive dating methods." After I left the faith I actually went down the Phoenix Public Library main branch and found the November 1979 Popular Science article that contains this quote. I've copied the full quote (see below) from Jan Haugland's website where I found a copy. You'll notice of course PopSci calls Gentry's views "odd speculations" and offers this information mostly to show somethings are still unknown. Elsewhere I've read that Gentry is a Seventh Day Adventist and believes in a literal interpretation of Genesis that involves believing the Earth is not much older than 6000 years.
In terms of how the Witnesses used the quote, you don't have to get into the U238 / Pb206 ratios, to see dishonesty. PopSci could just as easily said "elephants" or "rivers" or "polar icecaps" where the word used is "man." But if it had, the quote wouldn't have worked for the Witnesses, because they hold the very odd position of old earth, but young age for the history of mankind.
Not having an explanation for some anomaly does not mean Dr. Gentry has built a case against every other line of evidence. Certainly layers of ice at the poles are also a measure of time and they go far beyond the time frame of the Genesis creation account as well as the global flood of Noah's day. Rates of change in MtDNA is yet another measure of time. A literal understanding of Genesis would compel us to believe all of us have MtDNA from Eve who was the first human female and she lived just over 6000 years ago. His comment about "rates of decay" not varying being an "untestable assumption" means what exactly? Basically it would mean fundemental physics of radiation is not understood. Actually the reliability of the laws of nature is an important reason why we know anything at all.
Cheers,
-Randy
ps: Quote from PopSci...
So, today, everything -- human artifacts, animal remains, ancient rocks -- can be dated fairly accurately. The dates may be off a little, but that's mainly a matter of impurities in the sample or need to refine techniques, say the scientists involved. Yet major mysteries and curious anomalies remain -- the odd speculations advanced by Columbia Union College's Robert Gentry, for instance. Physicist Gentry believes that all of the dates determined by radioactive decay may be off -- not only by a few years, but by orders of magnitude. His theory revolves around "halos," tiny, ringlike discolorations found within coalified wood (wood on its way to becoming coal) and mica, often in the proximity of radioactive uranium or thorium. Some halos can be explained in terms of conventional radioactive decay. Others, known as giant halos, cannot. They're simply too big to be caused by alpha particles thrown off by known isotopes, and they don't fit into any accepted theory. If the theory of radioactive decay is weak in one spot, says Gentry, doubt is cast on whatever answers isotopes give you. Further, when Gentry studies halos in coalified wood, he finds that the uranium/lead ratios are often not at all what they should be. "Since the coalified wood was obtained from deposits supposedly at least tens of millions of years old," he says, "the ratio between uranium-238 and lead-206 should be low." They're not. They're so high, in fact, that "presently accepted ages may be too high by a factor of thousands." And man, instead of having walked the earth for 3.6 million years, may have been around for only a few thousand. "The possibility of reducing the 4.5-billion-year history of earth by a factor of a thousand," he says with some ire, "has not yet been seriously considered." Most scientists simply dismiss the idea. As one physicist told me, "You can believe it or not; I don't." "I realize it's difficult to believe," counters Gentry. "It would invalidate the whole underlying principle of radioactive dating: that the rates of decay are forever unvarying -- an untestable assumption.