ahem...
Then I could quip that any idiot who doesn't even know the difference between C14 and 14C (it's hard, but I'm resisting the temptation) has no business posting anything on any subject.
Without that, it is no more reliably truthful than The Onion.
So9
First, a quick recap of what the "too much Carbon-14" measurements may mean (bear with me please):
1. Systematic error in the testing equipment or methods.
2. External contamination.
3. Internal contamination (i.e., new Carbon-14 being produced within the sample in some manner).
4. All organic samples really *are* no older than 40,000 years.
5. Decay rates have varied in the past.
6. Bad data, dishonest reporting, sloppy technique, fabricated results, etc.
7. Some combination thereof, including the original authors' overburdened combo of "they indicate a max of 40,000 years because a) nothing died earlier than that *and* b) they're even much younger than those careful 40,000-year measurements indicate by an order of magnitude because *also* c) decay rates have changed drastically from time to time *and* d) so have production rates". Uh huh...
From the original article in this thread:
#1 seems ruled out by the repeatability of the results for different samples, and the fact that some samples measure just fine at "damned little C-14" as expected. Although it would still be possible that something about the testing methods may produce spurious results only when applied to samples with certain compositions, but that's unlikely.
#2 seems ruled out by the many methods which were used to try to "wash away" external contaminants.
#3 seems possible, and that's the direction I was leaning, but some quick back-of-the-envelope calculations led me to think that they might not be able to account for as much C-14 as was measured (although I'm hardly a nuclear physicist, and may have overlooked some possibilities).
#4 is incredibly implausible on its face, for reasons I've given earlier -- there are just *too* many other lines of evidence that firmly indicate that the Earth really is quite old.
#5 is highly unlikely, *no* evidence has been found that decay rates have ever fluctuated while we've been monitoring them, nor that they ever have in the past (since that would have left tell-tale signs).
#6 is tempting, but... Other than the fact that I think it's pretty sloppy to try to compare readings from multiple researchers across multiple labs across multiple years (since their techniques and precisions and equipment are all likely to vary), I'm willing to give the authors and the researchers they cite the benefit of the doubt.
#7 is... Imaginative, but unlikely cubed. Not only does it postulate *multiple* outlandish deviations from established principles of science just to "reconcile" one anomalous finding, but it flies in the face of innumerable other findings which are much better supported *and* its proposed solution would have caused countless other noticeable effects (like, say, a million-fold increase in natural radiation which would have flash-fried Noah) which simply are not the case.
So since we seem to have eliminated -- or at least cast strong doubt on -- all possibilities, what the heck *is* the explanation for the results?
I can't resist a good puzzle, so I've been researching this question off and on all day. I've learned a lot of interesting things in the process (and expanded my IE bookmarks even further), but I think I hit paydirt when I came across the following:
Oh look, someone's broken the "radiocarbon barrier". And the fact that they did it with a new method for removing external contaminants seems pretty convincing evidence that the "radiocarbon barrier" was due to, well, external contaminants. Looks like those prior researchers weren't off-base after all (the ones that the authors of the PDF sneered at for attributing the results to contaminants).Abstract
New dating confirms that people occupied the Australian continent before the earliest time inferred from conventional radiocarbon analysis. Many of the new ages were obtained by accelerator mass spectrometry 14C dating after an acid–base–acid pretreatment with bulk combustion (ABA-BC) or after a newly developed acid–base–wet oxidation pretreatment with stepped combustion (ABOX-SC). The samples (charcoal) came from the earliest occupation levels of the Devil's Lair site in southwestern Western Australia. Initial occupation of this site was previously dated 35,000 14C yr B.P. Whereas the ABA-BC ages are indistinguishable from background beyond 42,000 14C yr B.P., the ABOX-SC ages are in stratigraphic order to ~55,000 14C yr B.P. The ABOX-SC chronology suggests that people were in the area by 48,000 cal yr B.P. Optically stimulated luminescence (OSL), electron spin resonance (ESR) ages, U-series dating of flowstones, and 14C dating of emu eggshell carbonate are in agreement with the ABOX-SC 14C chronology. These results, based on four independent techniques, reinforce arguments for early colonization of the Australian continent.
-- From Early Human Occupation at Devil's Lair, Southwestern Australia 50,000 Years Ago (published online 11 March 2002)
Note the interesting parts of the abstract, which I've highlighted in color.
The green portion notes that this is a new technique for removing contaminants.
The red portion is key -- it notes that although older pretreatments for eliminating contaminants still showed the 40,000-year-old "radiocarbon barrier", the new technique allowed readings way beyond 40kya -- up to 55,000 years. Furthermore, in a NERC grant, one of the authors was granted 19,627 British pounds to develop a facility to apply the technique in greater volume, with claimed ability to read dates up to 60,000 years.
Furthermore, the technique is shown to not just produce higher numbers by some means, but to do them accurately, as matched against the results of four other independent dating methods (blue text).
So to summarize:
1. The PDF authors concluded that the "radiocarbon barrier" was due to some real feature of the specimens (i.e., they all really did die "recently") and pooh-poohed the notion that it was due to contaminants. However, the fact that a particular technique can make specimens read older than the proposed "barrier" *and* match the results of other independent dating methods pretty much blows that one out of the water.
2. The fact that a contaminant-removing method has succeeded in overcoming the "barrier" indicates that the barrier was indeed caused by contaminants.
3. The fact that the dates "uncovered" by the method make sense (i.e. are consistent with the origin of the specimens and their relationship to each other and to younger specimens) and match four independent dating methods very strongly indicates that the findings are "real" and not artifacts of the processing method.
4. The new higher results can't be the result of "washing out" too much of the original Carbon-14 -- C-14 dating is done by measuring the ratio of C-14 to C-12 within the sample, and this will remain constant despite vigorous "washing" because any cleaning method is going to remove proportionately equal amounts of C-14 and C-12 because they are chemically identical.
5. At its upper limits, contamination will always be a problem for techniques like C-14 dating which rely on measuring the amount of very trace amounts of material. Even at the best of times (i.e., before an organism's death) Carbon-14 only makes up 0.0000000002% (not a typo) of the Carbon in the organism. *Very* small amounts of additional C-14 will contribute a significant amount of "noise" to the measurements of the smaller amounts of C-14 present in an old sample. This is not an indictment of C-14 dating in general, though, since such contamination has a far smaller effect on the relatively larger amounts of original C-14 being measured in younger samples. It's only when stretching the technique to its upper end that contamination "noise" becomes almost as large (or larger) than the true amount you're attempting to measure. Previously, the best techniques would still leave enough contamination to swamp a 40,000+ year reading. With the new more effective ABOX-SC technique, the noise level has been pushed back to 60,000 years -- but it's still there. The authors of the PDF would have you believe that this is because there's always measurable amounts of "original" C-14 in all samples. But this does not follow. The much more mundane (and likely) explanation is that there will always be an unavoidable amount of modern C-14 creeping into everything, like the way that sand on a beach always gets into your socks and shorts no matter how you try to avoid it.
6. This is the sort of thing which would have been caught by peer-review publishing. That's one of the many reasons why it's valuable.
7. In reference [12] the PDF authors cite an earlier work by some of the same authors as the article I abstracted above, and their overview of it sounds rather like ABOX-SC, or an earlier version of it -- and yet they did not point out the breaking of the 40,000kya radiocarbon barrier. Call me suspicious, but I'm going to track down a copy of that earlier work and see whether the PDF authors glossed over its implications or presented it misleadingly (although it's possible that the earlier work had not yet achieved the above success). I'll report back after I do that.
The samples they are examining are either devoid or essentially devoid of carbon-14. They therefore can't measure the C14 decay spectrum, or apply x-ray fluorescence, as they might with a more modern sample, so they use an accelerator for mass spectrometry. That's fair, but it requires an exquisitely detailed understanding of the backgrounds, all the way down to the limits of their sensitivity.
They go on at length about how they expect to find no C14 in their sample, and how careful they were to avoid C14 contamination from more modern sources. That's a red herring, however, because that's not the only potential background to this technique. The technique essentially measures the charge-to-mass ratio of the nuclei in the sample. C14 has essentially the same charge-to-mass ratio as Zn70, Mo98 and Cd112, along with the potential atmospheric contaminants Kr84 and Xe126. Some of these are quite abundant, and in any of these samples they are bound to dominate the C14 by a large factor.
To be sure, the charge-to-mass ratios of these isotopes are not exactly identical, thanks to the curve of binding energy. But while they may be able to get good separation of the peaks, they will have a devil of a time understanding the tails, which will necessarily overlap at some level. This discussion should have made up the bulk of the paper, but I don't see it even mentioned anywhere.
And I haven't even brought up the possibility of contamination from incompletely ionized atoms within the accelerator. Couldn't they at least quote their estimates for these backgrounds? What is the shape of the C14 peak in their detector, and what data cuts did they use to bracket it? It's nowhere here. Did the shape of the measured C14 peak match their expectations? Blank out. It's as if they treated the accelerator as a black box that spits out abundances (of which they quote one).