Arguments against radioactive dating
Was Rb-87 or Sr-87 added to the rock by some unknown process?
Was one of them removed from the rock by some unknown process?
Sr-86 diffuses more quickly than Sr-87, and that has never been taken into account when isochrons are analyzed. Perhaps, but it’s rather tricky, because the rate of diffusion depends on the specific chemical and physical environment of each individual rock.
If the effects of diffusion can be taken into account, it will require an elaborate model that will most certainly require elaborate assumptions. Hayes suggests a couple of other approaches that might work, but its not clear how well. If you believe the earth is very old, then most likely, all of the radioactive dates based on isochrons are probably overestimates. I have no idea, and I don’t think anyone else does, either. I would think that the older the sample, the larger the overestimate.
As someone who has studied radioactivity in detail, I have always been a bit amused by the assertion that radioactive dating is a precise way to determine the age of an object.
This false notion is often promoted when radioactive dates are listed with utterly unrealistic error bars.
If those rocks really have been sitting around on the moon for billions of years, I suspect that the the wide range of physical and chemical processes which occurred over that time period had a much more profound effect on the uncertainty of the age determination.
Generally, we are told that scientists have ways to analyze the object they are dating so as to eliminate the uncertainties due to unknown processes that occurred in the past. Hayes has pointed out a problem with isochrons that has, until now, not been considered.
If some process brought Sr-87 into the rock, it probably brought different amounts of the atom into different parts of the rock, so the ratio of Sr-87 to Sr-86 won’t stay consistent from one part of the rock to another. He says that there is one process that has been overlooked in all these isochron analyses: diffusion.
If a consistent isochron is generated, however, we can be “certain” that no process interfered with the relative amounts of Rb-87 and Sr-87, so the radioactive date is a good one. Atoms and molecules naturally move around, and they do so in such as way as to even out their concentrations.
It would be hard to imagine that geologic processes could explain all these.
But Drs Humphreys and Baumgardner realized that there were too many independent lines of evidence (the variety of elements used in 'standard' radioisotope dating, mature uranium radiohalos, fission track dating and more) that indicated that huge amounts of radioactive decay had actually taken place.