I would like to respond to Kirk Bertsche’s review of the RATE team’s 14C project posted above. His main conclusion is that the radiocarbon in fossil organisms which the RATE team documents from the peer-reviewed radiocarbon literature, together with the radiocarbon we measured in our own suites of coal and diamond samples, is, in his words, “nothing more than contamination.”
By way of introduction, let me point readers to a section entitled ‘Coping with Paradigm Conflict’ in my chapter on 14C in the 2005 RATE book edited by Vardiman et al. In this section I provide some examples of how the radiocarbon community has dealt with the dilemma discovered soon after the accelerator mass spectrometry (AMS) method began to be applied to 14C analysis in the early 1980’s. This dilemma is that samples they expect to be 14C-free because of their supposedly old age (>100,000 years according to the standard geological time scale), instead routinely display significant and reproducible 14C levels, typically two orders of magnitude or more above the threshold sensitivity of the AMS system.
This unexpected finding led immediately to a thorough evaluation of every aspect of sample processing in an attempt to identify what most investigators logically assumed to be the result of contamination in their procedures. This earnest search for the source or sources of contamination led to dozens of papers in the peer-reviewed radiocarbon literature on various aspects of AMS methods. For obvious reasons, most of these studies utilized samples that ought to have been 14C-free given their position in the geological record. Although some relatively minor sources of contamination were identified and fixed, the main part of the 14C signal remained, particularly in the case of samples such as coal, wood, bone, and shell from living organisms. This is the reason that 14C levels in biological samples from deep within the geological record are so thoroughly measured and documented in the open radiocarbon literature.
So how does the radiocarbon community deal with this state of affairs? Even to the casual observer, the presence of significant levels of 14C, which has a half-life of only 5730 years, in biological samples which are supposed to be tens or hundreds of millions of year old cries out for explanation. First of all, researchers within the community have avoided publicizing the problem to outsiders. For the most part, they keep this state of affairs to themselves. And even among one another, they mostly act as if the issue does not exist. In addition, they have adopted some special terminology that prevents most outsiders from realizing the problem exists. One of these terms is ‘in situ contamination’. This term was invoked more than twenty years ago by Vogel et al. [1987] to account for the high level of internal 14C (0.44 percent modern carbon, or pMC) they established to be present in the anthracite coal they utilized in their study. When researchers employ this term, they generally mean that the 14C they are detecting was already inherent to the sample when it reached their laboratory. Just how it got there, they generally refuse to speculate. Their job is to measure the 14C in the sample. Just what the sample history may have happened to be before the sample reached their lab, they say, is not their concern.
Nevertheless, to keep this dilemma under largely wraps, most commercial labs apply a high ‘standard background’ to the samples they process. For several labs, this standard background is about 0.8 pMC, corresponding to a radiocarbon age of 40,000 years. This standard background value is subtracted from the 14C value the lab actually measures in each sample. If the resulting 14C value is zero or less, the lab reports an ‘infinite’ radiocarbon age. Since vast majority of samples for materials that ought to be 14C-free, because of their location in the geological record, have values less than 0.8 pMC, this procedure saves the laboratory the awkward difficulty of explaining to a customer why a coal sample, for instance, has a non-zero level of 14C.
Although Bertsche styles himself as an “accelerator physicist, formerly at a leading radiocarbon AMS laboratory,” it is clear from his post that, as far as radiocarbon measurement procedures and issues are concerned, he is a novice. If he were truly an insider, he would be fully aware of the history I just outlined and that fossil material throughout the Phanerozoic record routinely displays 14C levels hundreds of times above the intrinsic AMS measurement threshold. This reality is what has generated the scores of papers over the past 25 years, mostly by researchers at the AMS facilities, seeking to understand this highly unexpected state of affairs. Samples truly more than 100,000 years old should have no detectable 14C. But in reality, biological specimens generally thought to be tens or hundreds of millions of years old consistently contain levels of 14C that at face value would indicate these organisms were alive only thousands of years ago, as I have just indicated.
If Bertsche could understand the very papers to which he refers, he would immediately realize his that his first claim that laboratory contamination is responsible of the high 14C levels routinely measured in ‘old’ biological samples is unsustainable. To highlight the issues he is failing to grasp, I point to the paper by Brown and Southon [1997] who state
Several “14C-free” background materials were used in obtaining these data: 1) Coal (supplied by Beta Analytic), 2) Calcite (TIRI sample F: Icelandic doublespar), 3) QL4766 wood (> 56.6 ka BP), 4) QL1428 wood (>55 ka BP), and 5) Yale Anthracite (YA-13; no measurable 14C activity). The latter three samples, and their 14C contents, were supplied by the Quaternary Isotope Laboratory, University of Washington (Stuiver, pers. comm., 1996). In our measurements there were no significant differences between the results obtained for these background materials, and the data from all these materials were used.
In Figure 2 these authors plot their own measurements for the 14C levels in what they describe as “14C-free” background materials for varying sample sizes. What a novice reader of the paper can easily miss is that the plot shows that these materials converge to a value of 0.25 pMC for larger sample sizes! The value should be zero for truly 14C-free material. The measured value is 14C some 450 times higher than the threshold for the AMS hardware. That is why the authors use quotation marks with the term “14C-free”. The AMS insiders understand the lingo. Bertsche apparently does not. (It is noteworthy that their value of 0.25 pMC, based on two coal samples, two wood samples, and a calcite, is almost identical to the mean value that the RATE team obtained for its suite of ten coal samples.)
Because of his shallow grasp of the issues, Bertsche throws out a number of ‘red-herrings’. He invokes the fact that over the years many AMS labs have established that their procedures routinely introduce tiny amounts of modern carbon (with today’s level of 14C), typically on the order of 1 g, into the samples they process. This level of contamination becomes serious for tiny sample sizes, say, 1 mg or less, especially if the sample is old. On the other hand, 1 g of contamination has negligible consequences when the sample size is on the order of 100 mg, as was the case for the samples we tested and reported. Bertsche fails to point out the very basic reality that AMS labs normally require a large enough sample such that this issue does not affect the precision of their measurement. For most of the 14C values reported in the peer-reviewed literature which I list in my chapter in the RATE book [Vardiman et al., 2005] the investigators had plenty of material available and so small sample size was just not an issue.
Bertsche also makes a ‘red-herring’ of the choice of samples I selected from the peer-reviewed literature to include in the category of non-biological Precambrian. He complains that I excluded two graphite samples that had been oxidized to CO2 and then reduced to graphite again. I did this deliberately, since it was clear from the references that these samples had been reprocessed and I was seeking to compare apples with apples to get as clear a picture as possible what the 14C level in non-biological Precambrian carbon might be. Surprisingly, he displays a serious lack of familiarity with the terms used to describe the geological time scale. Instead of Pre-Cambrian or perhaps Proterozoic, he substitutes the incorrect term Paleozoic.
Bertsche further reveals the shallowness of his understanding of AMS procedures and terminology by referring to the entire process of converting a sample to graphite as ‘graphitization’. Standard sample processing involves several steps, first an acid-base-acid sequence of washing to remove possible surface contamination, then conversion of the carbon in the sample to CO2, either by dissolving the sample in acid, if it is a carbonate, or by direct oxidation via combustion, and finally reduction of the resulting CO2 to graphite, usually as a graphite coating on iron or cobalt powder in the presence of hydrogen at about 600 C. Only the last step in this overall process is referred to by people in the radiocarbon community as ‘graphitization’. The paper by Kirner et al. [1995] to which Bertsche refers describes these sample processing steps in detail. Contamination can occur during any one of these steps, but the AMS labs have developed techniques for minimizing it and also for detecting when something has gone awry. None of the papers to which Bertsche refers identifies the final graphitization step as the main culprit as far as the overall sample processing contamination arising is concerned. Just why he uses the term ‘graphitization’ in the peculiar manner he does is a mystery.
Moreover, Bertsche is simply in fantasy land when he then claims “the graphitization process typically add[s] from 0.1 to 0.7 pMC (highly dependent on sample size and procedure).” This is absurd. He cannot support such claim from any peer-reviewed source. It is certainly not to be found in any of his references. In fact, the papers to which he refers all clearly refute such a notion except for atypical sample sizes. Hence, Bertsche’s statement that “the differences [Baumgardner] sees between geological and biological samples is simply the contamination introduced by the graphitization process” is flatly unsupportable. Dozens of papers in the peer-reviewed literature irrefutably demonstrate this, as I point out in my chapter in the RATE book. If Bertsche disagrees, let him clearly show why all these AMS specialists are wrong!
Bertsche produces still more ‘red-herrings’ to create confusion about the RATE 14C measurements on its ten coal samples. First, he quotes the scientist who actually performed the AMS measurements to the effect that the coal samples “were contaminated in situ.” Again, one needs to understand what this terminology means to an AMS insider. To an AMS insider, “contaminated in situ” means simply that the 14C measured by the AMS system was intrinsic to the sample before it arrived at the laboratory; in other words, such 14C is not a result of laboratory procedures.
Bertsche then tosses out several possible ways the coal might have acquired its inventory of 14C in its natural setting. He first mentions the presence of uranium and alludes to northern Australian coals. Northern Australian coals? Just where, pray tell, might they be found? In regard to 14C production due to the presence of uranium in crustal environments, I treat that topic in detail in section 7 of my chapter and show the maximum plausible 14C production rate, given measured neutron fluxes in deep mines and measured reaction cross sections, is more than four orders of magnitude too small to account even for the small measured 14C levels in diamonds. This same analysis also applies to coal. Uranium concentrations in coal are typically less than those measured for granite, which is the setting for most of the diamonds we studied. (See the USGS fact sheet on uranium concentrations in coal and granite in the References.)
Next, incredibly, Bertsche proposes microbial growth as a source of 14C! Just what does Bertsche imagine such microbes to be eating if it is not the coal itself? It they are eating the coal, then how can the 14C levels within them be any different from that of the coal itself? Talk about grasping for straws.
Next Bertsche resorts to speculating that our coal samples were contaminated while in storage “in a DOE geology lab refrigerator.” To me that smacks of a deliberate distortion of what I described in my chapter on pages 605-606 regarding the pedigree of the samples we acquired from the U. S. Department of Energy Coal Sample Bank at the Pennsylvania State University. I emphasized the careful procedures applied in the collection and preservation of these samples. They were sealed under argon to preclude contamination from just moments after they were collected. For most of their lives these samples were sealed in argon in multi-laminate foil bags and refrigerated at 3 C. Just why does Bertsche choose to engage in this sort of distortion? To me it suggests a significant level of desperation in the face of such obvious evidence for the presence of genuine intrinsic 14C in these samples.
Note that in attempting to explain the 14C in our coal samples as contamination outside the lab, Bertsche is undermining his earlier arguments that the nearly identical 14C levels reported for coal and wood by AMS research scientists in the peer-reviewed literature are readily attributable to contamination within the lab. So which is it? Bertsche cannot have it both ways. Indeed, the preponderance of papers, written by AMS specialists, show that the 14C levels routinely measured for coal and other fossilized organic remains are not the result of contamination within the lab. The RATE coal measurements merely serve to affirm this already well established fact.
Finally, Bertsche seeks to dismiss the 14C we measured in diamonds also as contamination. He cites a 2007 paper by Taylor and Southon. The paper describes the techniques the authors recently applied to measure 14C levels in natural diamond. As part of the background of their paper, Taylor and Southon list six potential sources of contamination for samples analyzed in AMS laboratories. At the very top of their list is “(1) Pseudo 14C-free sample: 14C is present in carboniferous material that should not contain 14C because of its geological age”. By placing this item first, they acknowledge what has long been known by AMS radiocarbon specialists, namely, that the vast majority of samples that ought to be completely 14C-free because of their geological context display 14C levels far beyond what can be accounted for by sources attributable to laboratory procedures or equipment design.
Indeed, they implicitly acknowledge this in the first paragraph of their introduction by mentioning 14C ages of 47.9 ka for a marble sample and 52.1 ka for a Pliocene wood sample, both far beyond the AMS 100,000-year detection limit they mention in their first sentence. It is astonishing that these authors never attribute this discrepancy to any one of the six possible explanations they list later in the article. In fact, they are completely silent as to just what the correct the explanation might be. This silence is all the more noteworthy since the 14C level in the marble sample is 546 times the detection limit of their AMS system.
The main point of their paper is that by using diamonds and mounting them directly in the sample holder, they are able to exclude items (2) through (5) in their list of six potential sources of contamination. These items are (2) Combustion/acidification background, (3) Graphitization background, (4) Transfer (to the sample holder) background, and (5) Storage background. The last item in their list is (6) Instrument background involves a “14C signal registering in the detector circuitry when 14C-ion [is] not present.” This item is routinely and reliably tested by running the system with no sample in the aluminum sample holder. This test is the basis for the value of the ultimate AMS detection limit, about 0.0005 pMC, corresponding to about 100,000 14C years. Therefore, by process of elimination, what these authors are measuring and reporting is their item (1), namely, 14C intrinsic to the diamonds! This is precisely what we claim for diamond samples we measured using the same technique.
Taylor and Southon report results from eight individual natural diamonds and from six separate fragments cut from a single diamond.
The 14C values ranged from 0.005 to 0.021 pMC for the eight individual diamonds and 0.015 to 0.018 pMC for the six fragments, with typical uncertainties of ±0.001-0.002 pMC. Note that a value of 0.015 exceeds the AMS system background value by a factor of 30.
I certainly grant that one needs almost to be an AMS insider to be aware how routine it is to measure the sixth item in Taylor and Southon’s list, instrument background, and hence to realize that the 14C values they report represent intrinsic 14C in the diamonds themselves and not instrument background. It is therefore understandable why Bertsche comes away with an incorrect conclusion after reading their paper. This illustrates again, however, that he is not the expert in 14C dating that he makes himself out to be.
What about the RATE diamond measurements? Bertsche alludes to the fact that the RATE team also tested diamond by placing diamonds directly into the AMS sample holder. Our tests were done in 2006 after the RATE book was published in 2005. We obtained results quite similar to those reported by Taylor and Southon in 2007. Our ten diamond samples displayed 14C values between 0.008 and 0.022 pMC, with a mean value of 0.014 pMC. Certainly these 14C levels are much smaller than what we obtained for our coal samples, so caution is obviously advisable in their interpretation. Nevertheless, unless one has a philosophical bias against such a possibility, the most plausible explanation, astonishing as it may be to some, is that natural diamond contains measurable and reproducible levels of intrinsic 14C.
In summary, Bertsche fails to make his case that the radiocarbon in fossil organisms described so frequently in the peer-reviewed radiocarbon literature, as well as the radiocarbon we document in our own coal and diamond samples, is “nothing more than contamination.” In light of this discussion, I urge him to take a fresh new look at the issues involved, especially the rationale and techniques we used to reach our conclusions.
References
Brown, T. A. and J. R. Southon, Corrections for contamination background in AMS 14C measurements, Nuclear Instruments and Methods in Physics Research B, 123, 208-213, 1997.
Kirner, D. L., R. E. Taylor, and J. R. Southon, Reduction in backgrounds of microsamples for AMS 14C dating, Radiocarbon, 37(2), 697-704, 1995.
Radioactive Elements in Coal and Fly Ash: Abundance, Forms, and Environmental Significance, USGS Fact Sheet, FS-163-97, 1997 (
http://greenwood.cr.usgs.gov/energy/...FS-163-97.html )
Taylor, R. E. and J. Southon, Use of natural diamonds to monitor 14C AMS instrument backgrounds, Nuclear Instruments and Methods in Physics Research B, 259, 282-287, 2007.
Vardiman, L., A. A. Snelling, and E. F. Chaffin (eds.), Radioisotopes and the Age of the Earth: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, CA and Creation Research Society, Chino Valley, AZ, 2005, Chapter 8, 587-631. [An earlier version of this chapter was presented at the 2003 International Conference on Creationism, and this paper in pdf format may be downloaded at
http://www.icr.org/pdf/research/RATE...aumgardner.pdf .]
Vogel, J. S., D. E. Nelson, and J. R. Southon, 14C background levels in an accelerator mass spectrometry system, Radiocarbon, 29(3), 323-333, 1987.
