What with biochemical isotope effects and likely differences in the age of the carbon sources fed to the anthrax organism during growth, I find it extremely difficult to believe that radiocarbon dating alone could reliably give an age of less than two years. Unless the FBI knows the exact isotope ratios of the nutrients fed to the anthrax organism, they can’t have a reliable starting point for their calculations.
Without that, the ~0.012% decrease in C[sup]14[/sup] per year, from an unknown starting point, is an awfully small nail to hang a hat on.
Does anyone have information on how the age determination was actually carried out ? Maybe they calibrated with viability studies or amino acid racemization data ?
Are there no other isotopes one could look at? Can’t you use similiar technologies with thorium or potasium? The journalists would probably still cal it ‘radiocarbon’, as it sounds familiar.
Just a guess, ws I cannot remember the half-life of any of the common thorium isotopes.
[sub]OK, consider this post a bump[/sub]
I agree that you wouldn’t be able to do it with carbon dating because of the lack of precision and the fact that the raw materials could have been sitting around for a while. I don’t think AAR would work because it’s temperature-dependent and no one knows if the spores have been kept in a freezer or whatever. The same is probably true of viability studies.
According to the news stories I’ve seen, this was something that was leaked by unnamed “officials” and not officially announced by the FBI, so I would take it with a grain of salt. If they really dated the spores somehow, they probably didn’t do it with carbon dating.
I also don’t see how one could accurately measure a 2 year lifetime using carbon-14 (5730 year half-life). As for the other suggestions above, potassium has no isotopes with useful half lives (they’re < 1 day or about a billion years). Thorium-228 has a convenient half-life of 1.913 years, and other isotopes have ~20 day half-lives, so if actively growing organisms take in these isotopes, you could probably use Th-228 dating to measure how long spores have been inactive.
There haven’t been any denials of the story, so I’m inclined to think it contains at least a grain of truth. We’ll find out for sure if the FBI now narrows its list of supects by a factor of ten or so. The question remains though, how would you measure a date like that ?
Thermoluminescence seems unlikely, and I don’t think anyone actually counts the tracks of gamma-rays in biologically derived crystals. What does that leave ? Showing that the strain of Anthrax was identical to one first isolated in the last few years, or that the powder contained dateable byproducts of the purification process would suffice, but those methods would also give a lot more information about the possible identity of the evil-doer.
I suppose it’ll all eventually come out, if they catch the guy.
It seems likely to me that the method used was Accelerator Mass Spectrometry (AMS), which is generally used for very small samples. According to this site, error can be as small as 0.005%. I do not know how that translates to a specific time period, or whether such error is small enough to date a sample to within two years before present.
Real world application, however, seems to hover around 0.4%-0.5% accuracy (which seems to translate to something on the order of +/- a few decades).