Comments?
I’d love to hear!
Robert Gentry is a young-earth creationist. He thinks the world came into being, more or less just as it says in Genesis, a few thousand years ago. Among young-earth creationists he has the distinction of having published research on the subject in a mainstream, peer-reviewed, scientific journal. What he argued is that the polonium radiohalos found in basal granites are not consistent with standard geo-physical accounts of the formation of those granites over millions of years. Instead, for the radiohalos to be formed, the basal granites must have been formed very quickly. If they had been formed by slow cooling of molten rock, the polonium halos would be entirely dissipated. To Gentry, at least, this suggests that the basal granites might have been formed in an instant at God’s command.
There’s a basic problem with his arguments. To be clear about it, we need to keep several issues separate. First, what is the relevance of the arguments if they are correct? Do they support the conclusion that the earth is young? The answer to that is: Not much. His argument is that the radiohalos show that basal granites were formed quickly. That is not, by itself, any argument at all that they were also formed recently and so does not support the contention that the earth is young.
It may, however, be indirectly relevant in the following way: It removes one of the props for the position that the world is very old – namely, that it must be at least old enough for the granites to have been formed slowly. Suppose that were combined with evidence that all basal granites were formed quickly (I’m not sure if he thinks he has this or not) and also with evidence that all other presumed-to-require-long-periods-for-formation features of the earth could be or must have been formed quickly. If he had all that, it could begin to add up to a case for a young earth. I’m pretty sure he hasn’t provided anything much like that additional body of evidence.
Before passing on to other matters, let’s take a bit closer look at what kind of further evidence Gentry would need to begin to make an impressive case for a young earth. Note that an argument that A and B each could have occurred quickly is not necessarily an argument that both could have occurred quickly. The conditions under which A could occur quickly might be conditions under which B could not. A further complication is that saying that A could have occurred quickly does not directly support saying that it is plausible, in realistic natural environments, that A did occur quickly. In the video I saw (The Young Earth, based largely on Gentry’s work), I noticed careless transitions of this sort: from ‘coal can be formed quickly (under specially designed laboratory conditions)’ to ‘coal can be formed quickly (in natural history)’ to ‘all coal could have been formed quickly’ to ‘all coal was formed quickly.’ Plainly, the core laboratory evidence only partially supports the second claim, provides less support to the third, and still less to the fourth.
Anyhow, Gentry’s work on radiohalos does not do much to support a young earth. At the very least, it would need substantial supplementation from other kinds of evidence.
But there is a second point that has apparently and amazingly gone unnoticed, at least by young-earth creationists. Gentry’s entire argument that basal granites must have been formed quickly depends on the reliability of radiometric dating. (More precisely, it depends on the constancy of radioactive decay rates. But if decay rates are constant, then radiometric dating is reliable.) If radiometric dating is not reliable, he has no argument at all, no case whatsoever, for the rapid formation of basal granites. Running that in reverse, if Gentry can show (by means of the arguments he has presented) that basal granites were rapidly formed, that implies that radiometric dating is reliable. But if radiometric dating is, in general, reliable, then, because of the results of other applications of radiometric dating procedures, we know the earth is very old.
To avoid the latter conclusion – that radiometric dating shows the earth is very old – Gentry elaborates his position to the point of pretty obvious self-contradiction. He claims radioactive decay rates have changed and that we therefore cannot trust any radiometric dates extending back before the supposed Great Flood. Now, the supposition of changing decay rates is physically preposterous; there are deep reasons in quantum physics for holding that substantial changes are virtually impossible. But let’s waive that: if it were true that there had been substantial and coordinated change in decay rates for all samples much beyond the fairly recent past, it would cut all the ground from under Gentry’s arguments that basal granites were formed quickly. His position can’t possibly be correct.
There’s still a third point to be raised with respect to Gentry’s case. What are those (like me) who take radiometric dating to be reliable to make of Gentry’s evidence? This, it seems to me, is a real difficulty, though it only arises for people who reject the forlorn notion that the earth is only a few thousand years old. I’m not sure what to say here. Taken at face value, the radiohalos seem to show that at least some basal granites were formed quickly. As far as I know, there is no widely accepted or well-supported theory about how that might have happened. Trying to come up with such a theory might be a fruitful avenue of research. Alternatively, so might trying to come up with an explanation for the radiohalos that does not involve rapid formation of basal granites. But, for those not involved in either of those research projects, the appropriate attitude would seem to be simply to treat the radiohalos as anomalies, as yet unexplained, while recognizing that, whatever the outcome of those research programs, the evidence that the earth very old is, by any reasonable standards, quite decisive.
As an aside, I’ll mention a couple of earlier scientific dating "scares" that, at the time, appeared to pose problems for evolutionary theory. Both were noticed in the latter part of the 19th century and both, if correct, would have shown that there were fundamental problems for evolutionary theory.
1) Fleeming Jenkin pointed out that, on the prevailing "blending" theory of heredity, there wouldn’t be time for a new, advantageous trait to spread through a population before it was diluted to insignificance. If the prevailing theory had turned out to be right, evolution by Darwinian mechanisms would be impossible. In fact, however, it was the prevailing theory that went – on the basis of Mendel’s independent evidence – in favor of an account of particulate inheritance.
2) William Thomson (Lord Kelvin) calculated that known physical processes could only have kept the sun burning for seventy to a hundred thousand years. There was nothing wrong with his calculations, relying, as they did, on what was then known about chemical combustion. He inferred that since the calculated time span wasn’t long enough for evolutionary processes to work, there must be something wrong with the evolutionary theory. What we know now is that the argument would have been better run in the opposite direction: Since evolutionary processes had worked and had taken longer (because they must have taken longer) than 70-100,000 years, there must be other, then unknown, processes that could keep the sun going for longer. Of course, in the early years of the 20th century, the nuclear processes that were up to the task were discovered.
In both cases, it was evolutionary theory that survived and the apparently inconsistent evidence or theorizing that turned out to be itself incomplete or in need of reinterpretation. Gentry’s evidence, though hardly as serious a challenge to evolutionary theory as Jenkin’s or Thomson’s, can be expected to go the same way.
