YEC Best Evidence 7: ancient carbon-14 — intrinsic or contamination?

Posted at 10:00 on 04 December 2017

One common thread that turns up time and time again in young-earth arguments is taking a scientific dating technique, pushing it to breaking point, and claiming that because it doesn't always give the correct results at the extremities, that automatically means that all conventional old-earth dating methods are hopelessly broken everywhere.

It's a bit like trying to bake a cake by using a weighbridge — the huge scales that are normally only used to weigh ten ton lorries — to measure out your butter, eggs, flour, sugar and fruit, then, when the results turn out all mushy and inedible, claiming that this proves that Jamie Oliver, Mary Berry, Nigella Lawson, Gordon Ramsay, and Ina Garten haven't the faintest idea about cooking.

Why do ancient coals and diamonds contain carbon-14?

The seventh of Answers in Genesis's ten best evidences for a young earth is one such example of this argument. It is the claim of the RATE project that they had found carbon-14 in ancient coals and diamonds. Carbon-14 has a half-life of 5,750 years, and samples more than a million years old should not contain any detectable radiocarbon at all. So what is going on?

The RATE project's complete technical report, written by John Baumgardner, starts off with a listing of samples in the scientific literature that should, in theory, have no measurable radiocarbon. It summarises the listing with two histograms:

The first point to note here is that the amount of radiocarbon found in each case was low. Radiocarbon results are often quoted as a percentage of modern carbon-14 levels (pMC or %MC) with modern levels being approximately one molecule of carbon-14 to every 10¹² (one trillion) molecules of carbon-12. The RATE team reported that Precambrian (non-biological) samples give results of 0-0.12 pMC, while Phanerozoic (biological) samples give 0.05-0.65 pMC. These figures are comparable to the levels obtained from studies of known contamination mechanisms.

Yet Answers in Genesis dismisses contamination as "rescuing devices" and "hackneyed defences."

"Rescuing devices" or sloppy science?

Contamination is no mere "rescuing device"; it is a systematic error. Systematic errors have to be accounted for and eliminated before any conclusions can be drawn: this is one of the first things that you learn in a first year undergraduate physics practical class. To dismiss contamination — or any other kind of systematic error — as a "rescuing device" or a "hackneyed defence" in this cavalier manner encourages Christians to adopt a sloppy and indisciplined approach to science that, in any other area of scientific inquiry, would kill people. (The pharmaceutical industry is just one example that comes to mind here.)

Andrew Snelling makes the following claim about contamination:

Yet for thirty years AMS radiocarbon laboratories have subjected all samples, before they carbon-14 date them, to repeated brutal treatments with strong acids and bleaches to rid them of all contamination. And when the instruments are tested with blank samples, they yield zero radiocarbon, so there can’t be any contamination or instrument problems.

This claim is not true. "Repeated brutal treatments with strong acids and bleaches" will in fact introduce modern carbon-14, not eliminate it. Preparing samples for carbon-14 dating is a complex process; the samples have to be combusted to convert them to CO₂ and then chemically reduced to graphite. Furthermore, many samples need to be chemically separated — for example, to extract cellulose from wood or collagen from bone. Every step in the process will introduce more contamination. This is why the Precambrian samples gave lower readings than the Phanerozoic samples — because they were already simple graphite, they typically only required a mechanical surface cleaning.

For what it's worth, this is not merely a "uniformitarian assumption of evolution and millions of years." The effects of processing on carbon-14 levels have been studied and characterised extensively, with whole journals such as Radiocarbon dedicated to the subject. One way of doing so is to measure the radiocarbon in a sample, then subject it to further processing, then take a second reading and measure the difference between the two. In fact, two of the entries in Baumgardner's list — numbers 21 and 40 — report precisely this. They were from the same samples as numbers 62 and 79, but were recycled in order to try to characterise how much modern carbon would be introduced by pre-processing using methods such as the "brutal treatments with strong acids and bleaches" of which Dr Snelling speaks. The differences were 0.25pMC and 0.14pMC respectively, demonstrating that it takes just two or three steps of sample chemistry to introduce enough contamination to account for the levels reported.

Many of the other items on Baumgardner's list also included reports of similar studies characterising identifiable contamination vectors. AMS results after sample processing can be compared with radiation counting (for example by scintillation or a Geiger counter) beforehand, as was the case in sample 10. The ratios of carbon-14 to carbon-12 and carbon-13 can be studied. Results from different laboratories can be cross-checked.

In addition to sample chemistry, contamination can also be introduced in situ, for example, when coal is permeated by groundwater, or when nitrogen is bombarded by electrons from decay products of nearby uranium. It can also be introduced when the samples are collected, or when they are being packaged ready for storage.

Then there is instrument background.

Snelling claims that blank samples yield zero radiocarbon. Again, this claim is untrue. Kirk Bertsche, a physicist with extensive experience in AMS spectroscopy design and also in preparation of samples for carbon-14 dating, has a detailed critique of the RATE project's radiocarbon claims, in which he outlines several different potential sources of instrument background:

1. ion source “memory” of previous samples, due to radiocarbon sticking to the walls of the ion source, thermally desorbing, and then sticking to another sample
2. mass spectrometer background, non-radiocarbon ions that are misidentified as radiocarbon, sometimes through unexpected mechanisms
3. detector background, including cosmic rays and electronics noise

For a full treatment of the subject, I would recommend that you read Dr Bertsche's essay. His explanations come from years of experience designing and building the accelerator mass spectrometers used in radiocarbon dating, so he has extensively studied the different possible contamination vectors. He goes into some detail about how radiocarbon laboratories identify and characterise contamination — and he makes it clear that they do so with considerably more rigour and painstaking attention to detail than the RATE team would have you believe. Dr Bertsche is also an evangelical Christian, and as such, his interest in the subject is more out of concern for factual accuracy in our apologetics than in conforming to a particular ideology.

It is also important to note that potential sources of contamination have not been fully quantified, and that additional, as yet unknown contamination vectors could be at work. The current scientific consensus is that contamination in radiocarbon dating can reach levels of up to about 0.5 pMC. In any case, experimental error or sloppy laboratory procedure could also increase contamination, and consequently solid peer review and replication of the results are essential.

The study of solar neutrinos demands radiocarbon-free fossil fuels

It turns out that carbon-14 contamination is an important question in the physics community for reasons other than radiometric dating. Physicists studying solar neutrinos need to find sources of carbon that contain a ¹⁴C content of less than one part in 10²⁰. Kathleen Hunt has this to say about it:

It turns out that the origin and concentration of ¹⁴C in fossil fuels is important to the physics community because of its relevance for detection of solar neutrinos. Apparently one of the new neutrino detectors, the Borexino detector in Italy, works by detecting tiny flashes of visible light produced by neutrinos passing through a huge subterranean vat of "scintillation fluid". Scintillation fluid is made from fossil fuels such as methane or oil (plus some other ingredients), and it sparkles when struck by beta particles or certain other events such as neutrinos. The Borexino detector has 800 tons of scintillant. However, if there are any native beta emitters in the fluid itself, that natural radioactive decay will also produce scintillant flashes. (In fact that's the more common use of scintillant. I use scintillant every day in my own work to detect ¹⁴C and ³H-tagged hormones. But I only use a milliliter at a time - the concept of 800 tons really boggles the mind!). So, the physics community has gotten interested in finding out whether and why fossil fuels have native radioactivity. The aim is to find fossil fuels that have a ¹⁴C/C ratio of 10^-20 or less; below that, neutrino activity can be reliably detected. The Borexino detector, and other planned detectors of this type, must keep native beta emissions to below 1 count per ton of fluid per week to reliably detect solar neutrinos. (In comparison, my little hormone vials, here in my above-ground lab, have a background count of about 25 counts per minute for 3.5 milliliters.)

The upshot of this is that there is a strong motivation to determine not only where radiocarbon in fossil fuels comes from, but how to predict where to find deposits that don't have any. In the course of their research, the scientists concerned have discovered that carbon-14 levels in ancient coals vary widely, and strongly correlate with the presence of uranium deposits nearby:

So, the physicists want to find fossil fuels that have very little ¹⁴C. In the course of this work, they've discovered that fossil fuels vary widely in ¹⁴C content. Some have no detectable ¹⁴C; some have quite a lot of ¹⁴C. Apparently it correlates best with the content of the natural radioactivity of the rocks surrounding the fossil fuels, particularly the neutron- and alpha-particle-emitting isotopes of the uranium-thorium series. Dr. Gove and his colleagues told me they think the evidence so far demonstrates that ¹⁴C in coal and other fossil fuels is derived entirely from new production of ¹⁴C by local radioactive decay of the uranium-thorium series. Many studies verify that coals vary widely in uranium-thorium content, and that this can result in inflated content of certain isotopes relevant to radiometric dating (see abstracts below). I now understand why fossil fuels are not routinely used in radiometric dating!

The fact that there is a direct, measurable correlation between carbon-14 levels in fossil fuels and the presence of nearby uranium means that this can not be any kind of "rescuing device," but that it is indeed a real, measurable effect. And the fact that they need to get their hands on eight hundred tons of radiocarbon-free deposits puts this one into the same category as oil exploration in general: they are under strong incentives to come up with explanations that are correct rather than ones that are ideologically convenient.

"Radiocarbon of the gaps"

Now Dr Bertsche does admit that radiocarbon in ancient coals and diamonds can not always be fully accounted for by known sources of contamination. However, appealing to "intrinsic radiocarbon" is premature until and unless you have ruled out the possibility of unknown sources.

If "intrinsic radiocarbon" were indeed a viable explanation, we would expect to see it consistently across all kinds of samples, at levels well in excess of those that could be explained by contamination. We would not expect to see it in some materials but not in others, and we would certainly not expect different tests on the same samples to give significantly different results. Nor would we expect to see any kind of correlation with the presence of nearby radioactive rocks.

But that is not what is observed. As Dr Bertsche says, radiocarbon levels show many significant patterns that are simply not consistent with the "intrinsic" hypothesis:

While some materials, e.g., coals and carbonates, often do show radiocarbon contamination that cannot be fully accounted for, resorting to “intrinsic radiocarbon” raises more questions than it answers. Why do only some materials show evidence of this intrinsic radiocarbon? Why does some anthracite and diamond exist with no measurable intrinsic radiocarbon? Why is its presence in carbonates so much more variable than in other materials, e.g., wood and graphite? Why is it often found in bone carbonates but not in collagen from the same bone? Since intrinsic radiocarbon would be mistakenly interpreted as AMS process background, why do multi-laboratory intercomparisons not show a much larger variation than is observed? Why does unprocessed diamond seem to have less intrinsic radiocarbon than processed diamond?

The fact remains that not only are the levels of carbon-14 found in ancient coals and diamonds too low to rule out contamination, but they also follow trends and patterns that strongly indicate that this is the case. Given that contamination vectors have been extensively studied and quantified, it simply isn't realistic to dismiss them as "rescuing devices" or a "hackneyed defence." Young-earth advocates need to demonstrate that hundreds of thousands of other measurements are all consistently in error by factors of up to a million, and the reported levels of radiocarbon in ancient coals and diamonds fall far, far short of doing so.

Featured image credit: Wikimedia Commons