Are the RATE Radiocarbon (¹⁴C) Results Caused by Contamination?

Update

Dr. Baumgardner responded to Dr. Kirk Bertsche’s prior allegation of contamination in the RATE ¹⁴C results for diamond samples on this site in 2007 (included below). Dr. Bertsche later posted a revision of his first critique at http://www.asa3.org/ASA/education/origins/carbon-kb.htm and also at http://www.talkorigins.org/faqs/rate-critique.html that included the following claims regarding the ¹⁴C measurements on natural diamonds reported by Taylor and Southon (2007):

Taylor and Southon have also measured unprocessed diamond, finding a similar range of 0.005 to 0.03 pMC [percent Modern Carbon] without background subtraction. They interpret this result as their instrument background, primarily due to ion source memory. Their ion source current varied, unintentionally, over about a factor of two, perhaps due to crystal face orientation or to conductivity differences between samples. “The oldest ¹⁴C age equivalents were measured on natural diamonds which exhibited the highest current yields” [R.E. Taylor and J.R. Southon (2007) “Use of Natural Diamonds to Monitor ¹⁴C AMS Instrument Backgrounds,” Nuclear Instruments and Methods in Physics Research B259, 282-287.] This important observation provides evidence about the source of the radiocarbon.

If the radiocarbon were intrinsic to the sample, there would be no change in the radiocarbon ratio with sample current. The ¹⁴C, ¹³C, and ¹²C would change in unison. However, if the radiocarbon were coming from ion source memory or elsewhere in the accelerator, it should give a count rate independent of ion source current. Normalizing the radiocarbon count rate to the ion source current, which is predominantly ¹²C, would result in higher radiocarbon content for lower source currents, as observed. This data provides clear evidence that at least a significant fraction of the radiocarbon detected by Taylor and Southon in diamond measurements did not come from the diamonds themselves and thus could not be “intrinsic radiocarbon.”

After various requests for a follow-up on this, Dr. Baumgardner has prepared this response to these further claims by Dr. Bertsche:

In his 2008 critique Bertsche references the Taylor and Southon (2007) paper describing their application of accelerator mass spectrometry (AMS) to natural diamonds. Bertsche calls attention to the authors’ statement, “The oldest ¹⁴C age equivalents were measured on natural diamonds which exhibited the highest current yields.” He claims that this means that the measured ¹⁴C cannot be intrinsic to the diamonds themselves. What Bertsche fails to mention is that the correlation of low ¹⁴C level with high ion current was restricted to only a subset of the authors’ data. Such a correlation did not exist across all the samples the authors tested and reported. That pattern occurred only among the eight diamonds listed in part B of Taylor and Southon’s Table 2. Five of these diamonds were mounted with silver powder beneath them in the 1.6 mm holes drilled in the aluminum cathode sample holder, while the other three did not have the silver powder. The purpose of the silver powder was to enhance the thermal conductivity between the diamond and the aluminum sample holder. This difference in mounting procedure resulted in the surprising and unexplained increase in ion current and decrease in the number of ¹⁴C atoms detected as shown in part B of Table 2 for the samples without the silver powder.

How do the authors interpret this pattern? They state, “Previous tests showed that ¹⁴C count rates from silver powder cathodes were comparable with those from diamonds. Because of this and because the silver packing was largely shielded from the cesium beam by the diamonds themselves, the excess ¹⁴C was therefore probably due to differences between diamonds or run-to-run changes in the spectrometer, not from carbon in the silver powder.” Note that the authors emphatically do not attribute the higher ¹⁴C counts, as Bertsche claims, to ion source memory contamination. One good reason for the authors’ caution was the absence of this trend of higher ¹⁴C count with lower ion current in the measurements reported in part A of Table 2. Part A results are from a single diamond that was cleaved into six separate pieces. Results for these six samples show little variation in ¹⁴C levels despite moderately large differences in ion current. For example, samples 12674 and 12675 yielded the same ¹⁴C value of 0.015 pMC, despite the fact that sample 12675 displayed a 50% higher beam current compared with sample 12674. The correlation Bertsche is relying upon for his interpretation is altogether missing for the six samples listed in part A of Table 2. The simplest explanation for the trend in the eight samples in part B is that it is associated with the presence or absence of the silver powder. Precisely how the silver powder might be producing the observed trend is not clear. Indeed, the authors acknowledge their inability to provide a confident explanation.

Regardless of the actual cause, the glaring fact remains that Taylor and Southon detected levels of ¹⁴C in the diamonds they analyzed that were all well above the intrinsic sensitivity of their AMS hardware. That intrinsic sensitivity, typically observed with a blank aluminum sample holder (with no sample or silver powder present) is on the order of 0.00056 pMC, corresponding to about 100,000 years under the standard assumption of a constant past atmospheric ¹⁴C level. Note that the level measured for samples 12674 and 12675 are more than 25 times greater than this normal instrument background.

It is important to emphasize that placing the diamonds directly in holes bored in the instrument's cathode sample holder eliminates all of the potential sources of ¹⁴C contamination listed in Table 1 of Taylor and Southon's paper except for items (1), ¹⁴C intrinsic to the sample itself, and (7) instrument background. The authors argue that most potential sources of instrument background can be excluded for their system. They show from their investigations that contamination from CO₂ and other carbon-containing species adhering to the diamond surface can now be effectively ruled out as well. This means that contamination from ion source memory is largely removed from the table. What then is left? It is item (1), namely, ¹⁴C intrinsic to the sample itself! The authors acknowledge this reality in the final sentence of section 1 of their paper when they state, “¹⁴C from the actual sample is probably the dominant component of the ‘routine’ background.” This statement directly contradicts Bertsche's assertion that these authors interpret their measured ¹⁴C values as “instrument background, primarily due to ion source memory.” The overall conclusion is that the ¹⁴C levels in natural diamond reported by Taylor and Southon are consistently far above the levels one would expect if these diamonds were truly more than a few hundred thousand years old. Despite the conflict it raises for Bertsche’s worldview, the Taylor and Southon paper tangibly strengthens the case that AMS instrument background can be eliminated, to a high degree of certainty, even as a remotely possible explanation for the substantial ¹⁴C levels measured so routinely in carbon-bearing samples from deep within the geological record.

Furthermore, despite Bertsche’s emphasis on the diamond measurements, to me whether or not there is ¹⁴C in diamonds is a relatively minor issue. The dramatically more important issue, as emphasized in our RATE report, is the consistent presence of even higher levels of ¹⁴C in all fossilized living things which still retain some carbon. That fact is powerful and indisputable support that the earth is young and that the Genesis Flood really did occur not so long ago.

John Baumgardner
November 2014

Baumgardner’s Original 2007 Article

Kirk Bertsche recently posted a review of the RATE project’s ¹⁴C investigations on the TheologyWeb site (http://www.theologyweb.com/campus/showthread.php?t=103916 [last accessible, according to archive.org in 2012]). 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.” Below the quoted article is a response by Dr. John Baumgardner.

There have been a number of mentions in various threads of the ICR RATE project and its conclusions about radiocarbon. I have finally looked into this in detail (read their reports, read most of their references, and spoken with the expert who measured the radiocarbon samples for them.) My conclusions are below. (This is slightly modified from a post I made on the ASA mailing list, http://www.calvin.edu/archive/asa/200710/0173.html [Ed. note (2015): no longer available])

Baumgardner¹ claims to present experimental data showing that all biological material contains intrinsic radiocarbon, no matter how old it is claimed to be. He makes additional weaker claims that even non-biological carbonaceous material contains intrinsic radiocarbon. He presents two classes of data. Firstly, he re-analyzes radiocarbon AMS dates published in peer-reviewed scientific literature. Secondly, he presents results of samples which RATE has collected and sent to a leading radiocarbon AMS lab to be dated. In both cases, I am convinced that his “intrinsic radiocarbon” is nothing more than contamination.

Modern radiocarbon dating by AMS is a complex process with numerous opportunities for contamination. Taylor and Southon break the contamination into 7 general types, each of which can have multiple specific sources². The largest contamination component is generally the conversion of the sample to graphite; this introduces a small amount of modern carbon (typically at least 1 microgram³). Thus a 1mg sample of infinitely old carbon would measure at least 0.1 pMC (percent modern carbon) before background subtraction. Earlier techniques and malfunctioning equipment contribute more contamination. (Baumgardner does not seem to understand this; he wants to treat the quoted background from one of the leading modern labs as a constant value applicable to all labs and to all historic measurements.)

Baumgardner’s first class of data is previously-published radiocarbon AMS dates which he has re-analyzed. He has divided the samples into two groups: Paleozoic geological samples, and Phanerozoic biological samples. He claims that the geological samples have a mean radiocarbon content of 0.06pMC and the biological have a content of 0.29 +/- 0.16 pMC¹. But he fails to note that all of their geological samples are actually of geological graphite, so did not undergo the graphitization process which was required for the biological samples. In fact, two geological samples (entries 21 and 40 in his Table 1) were omitted from Baumgardner’s geological data histogram; these were identical to other geological graphite samples (entries 62 and 79 respectively) but were re-graphitized in the lab as controlled measurements of contamination from the graphitization process. These tests yielded characterizations of 0.25 and 0.14 pMC contamination from the graphitization process. Entry 10 in Baumgardner’s Table 1 compares radiocarbon AMS with the older radiocarbon decay counting, giving a roughly 0.4 pMC contamination level for AMS, mostly from graphitization. In fact, many of Baumgardner’s references include systematic tests for contamination, with the graphitization process typically adding from 0.1 to 0.7 pMC (highly dependent on sample size and procedure). It is quite clear that the differences he sees between geological and biological samples is simply the contamination introduced by the graphitization process. Further, the radiocarbon content of his selectively plotted geological samples of <0.1 pMC is in excellent agreement with the instrument backgrounds characterized in many of his references. Thus, the geological samples give no evidence of intrinsic radiocarbon.

Baumgardner’s second class of data consists of samples which the RATE team has collected and sent to be analyzed. This includes a set of 10 coal samples (0.25 +/- 0.11 pMC) and a number of diamond samples¹. Both materials are problematic in general, and even more problematic in the specifics of the RATE samples.

The expert who prepared and measured the RATE samples is convinced that the RATE coal samples were contaminated in situ. Coal is “notorious” for contamination, due to uranium which is often in or near the coal (especially a problem for N. Australian coals), from humic acids which are almost always present, and from microbial growth. The best coal dates reportedly come from anthracites with glassy surfaces, which have given dates as old as 70k years, or about 0.02 pMC.

It is also possible that the coal samples were contaminated while in storage for an indeterminate time in a DOE geology lab refrigerator¹. Geology labs often have elevated levels of radiocarbon due to tracer studies, neutron activation studies, and dust from uranium-bearing rocks. Carbon is highly mobile and contamination can spread through an entire lab and persist for decades⁴. (I have seen a badly contaminated sample which was traced to storage in a geology lab refrigerator.)

The diamond samples were difficult to graphitize, and apparently required some modifications to the normal procedure¹. This likely increased the contamination. In addition, the samples themselves were reportedly pitted and appeared to have been subjected to previous analyses of some sort. Nevertheless, the 5 deep-mine diamond samples were only slightly above background levels (0.01 to 0.07 pMC after background subtraction), while the 7 alluvial samples ranged from 0.03 to 0.31 pMC after background subtraction. Subsequently, this lab has inserted diamond directly into an ion source, eliminating the graphitization process, and has measured much older dates (unpublished). Taylor and Southon have measured 0.005 to 0.03 pMC by the same technique, which they interpret as their instrument background². This gives strong evidence that the RATE diamond samples were contaminated, either by previous testing or by graphitization.

Thus it is clear that the previous peer-reviewed radiocarbon AMS measurements can be explained by contamination, mostly in the graphitization process. The recent RATE coal samples were probably contaminated in situ, and the diamond samples were either contaminated in the graphitization process or by previous analyses. In any case, other coal and diamond samples have been measured at essentially the instrument background levels, giving no evidence for intrinsic radiocarbon. RATE’s claim that all carbonaceous material contains intrinsic radiocarbon is not supported by the data.

Kirk Bertsche—accelerator physicist, formerly at a leading radiocarbon AMS laboratory

References

1. Baumgardner, Radioisotopes and the Age of the Earth, vol. II, ch. 8. Everything except the diamond data is contained in this earlier paper: http://www.globalflood.org/papers/2003ICCc14.html
2. Taylor & Southon, NIM-B 259(2007)282ff.
3. Kirner et al, Radiocarbon 37(1995)697ff; Brown & Southon, NIM-B 123(1997)208ff; Mueller & Muzikar, Radiocarbon 44(2002)591ff; Southon, NIM-B 259(2007)288ff.
4. Zermeno et al, NIM-B 223-224(2004)293ff.

Baumgardner's Original 2007 Response

By way of introduction to my response, 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. [Editor’s note: Readers might also be interested in Radioisotopes and the Age of the Earth, Volume 1 (PDF).] 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 1980s. 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 5,730 years, in biological samples that 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 largely under 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 had fully understood the very papers to which he refers, he would immediately realize that his first claim that laboratory contamination is responsible for 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 µg, 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 µg 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 timescale. 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 incorrect 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 a 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? There are none of any significance in northern Australia. 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? It seems he’s grasping for straws here.

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 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 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, 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 look at the issues involved, especially the rationale and techniques we used to reach our conclusions.