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YEC Best Evidence 6: helium in radioactive rocks and the importance of critical peer review

This post is more than 6 years old.

Posted at 10:00 on 20 November 2017

Posts in this series:

  1. Sediment on the ocean floor
  2. Bent rock layers
  3. Soft tissue in dinosaur fossils
  4. The faint young sun paradox
  5. The earth's magnetic field
  6. Helium in radioactive rocks
  7. Carbon-14 in fossils, coals and diamonds
  8. Short-lived comets
  9. Salt concentration in the oceans
  10. DNA in ancient bacteria

Back in August, I wrote about the RATE project and its extraordinary claim that nuclear decay rates had been accelerated by a factor of a billion during the Creation Week and Noah's Flood. We also saw that they had reported some extraordinary problems with this hypothesis — notably, that it would have released enough heat to boil the oceans and melt the earth's crust many times over. Yet despite this, they were confident that these problems could be resolved, and at the same time they claimed that they actually had evidence to support their hypothesis. One of the claims that they made is the sixth of Answers in Genesis's ten best evidences for a young earth — that radioactive rocks contain too much helium.

Before I get into the technical details of this claim, I'll start by making one very important point.

Complex claims are easy to get wrong, difficult to get right, easy to fudge, and difficult to fact-check.

Quality control and quality assurance are of the utmost importance in science. Before a scientific study can be considered to have any credibility whatsoever, we need to ensure, for example, that:

  • It is free from arithmetic error;
  • It has identified samples correctly;
  • It took appropriate measures to minimise contamination, leakage, or other sources of error;
  • The integrity of the measurements themselves can be verified;
  • All relevant effects (temperature, pressure, anisotropy etc) have been taken into account;
  • The equations used are meaningful;
  • Any simplifications involved are small enough not to affect the overall result;
  • Relevant best practices in the area of study have been followed or demonstrably improved on;
  • Error bars are correctly calculated and correctly quoted.

There are three things to note here. First of all, failure to adhere to these standards will completely invalidate the results. Secondly, these examples that I have given have nothing whatsoever to do with "methodological naturalism", or "religious presuppositions" or anything else like that. An arithmetic error is an arithmetic error whether it is made by Andrew Snelling, Richard Dawkins, the Pope, or the Dalai Lama.

Thirdly, the more complex the study, the more likely it is that it will (initially at least) contain errors of this nature. Anyone who has ever worked as a software developer will be all too aware of this problem: bugs can all too easily creep into your code, and can very often have wide-ranging effects despite being subtle and difficult to spot. It is for this reason that computing pioneer Edsger W Dijkstra came up with the maxim that "simplicity is prerequisite for reliability."

The problem is compounded even more if the area of study concerned is particularly immature, with only a small number of published papers in the subject. This was certainly the case for helium diffusion studies at the time of the RATE project, as Jonathan Baker, a Christian geologist and author of the Age of Rocks blog, pointed out:

I am willing to bet that if you presented Dr. Humphrey’s research in detail to the geology department at any university, you would find a handful of geologists at most that would be able to follow the arguments without spending several hours reading up on the methodology. The modeling of helium diffusivity in zircon grains is a very complicated, math-intensive process that requires a particular expertise to apply properly. This method was developed only recently (hence the lack of data before 1999), and has been studied by a relatively small number of researchers over the past 10 years. The results can be extremely useful to geologists, and so hundreds of published studies have made use of helium data from zircons, but very few people are familiar with the laboratory procedure.

The upshot of this is that a study such as this one will need to be peer reviewed to within an inch of its life by subject matter experts — aggressively, mercilessly and relentlessly, and all the more so given that it is being made in support of an extraordinary claim about accelerated nuclear decay that would easily qualify for a Nobel Prize if it had any merit. To an untrained observer, this can appear petty and nitpicking, but it is essential. Anything less would also give a free pass to anti-vaxxers, homeopathy, astrology, water divining, reading tea leaves, and tobacco companies trying to prove that smoking does not cause cancer.

Do zircon crystals contain too much helium?

As we've already seen, zircons are tiny crystals of ZrSiO4 whose properties make them particularly well suited to uranium-lead radiometric dating.

When uranium decays to lead, it releases helium in the form of alpha particles, which then get trapped in the crystalline structure. Over time, these are expected to diffuse out of the zircons and into the surrounding rocks. If you know how much lead is in the zircons, you can calculate how much helium was produced by the decay. This value is called Q0. You can then measure the amount of helium that is left, Q, and calculate a ratio, Q/Q0, which tells you how much must have diffused out.

The RATE team studied some zircons that had been retrieved from a borehole in Fenton Hill, New Mexico, and concluded that this value, Q/Q0, was higher than it should have been given the zircons' radiometrically determined ages of 1.5 billion years.

They then came up with a "Creation model" that attempted to better explain the data. This model started off with a burst of accelerated nuclear decay giving rise to modern levels of uranium, lead and thorium, and an initial helium concentration, Q/Q0, of one. They claimed that when all the different values were plugged into their model, the final value of Q/Q0 = 0.58 indicated an age of 6,000 ± 2,000 years. This is pretty attractive to YECs, because very, very few of their claims of evidence for a young earth attempt to pin down its age precisely in this way — most of their other arguments merely attempt to discredit conventional old-earth results.

Simplifying assumptions.

Noble gas diffusion rates in crystals depend on a large number of different factors, including temperature, pressure, anisotropy (different diffusion rates in different directions), edge effects, and defects and impurities in the crystal structure. The theoretical calculations are complex, and it is very difficult to study it experimentally as well.

The RATE team's study makes several simplifying assumptions. There's nothing unusual or untoward about this: many models in physics do the same, otherwise the maths would be nightmarishly complicated. However, when you do so, you need to demonstrate that the simplifications concerned would not significantly affect your results.

The RATE team claimed that their simplifications would only affect the results by "a factor of two or so," or "an order of magnitude or so." However, they did not provide any calculations or other evidence to back up their claims that the effects were as insignificant as they claimed. Furthermore, factors of two or so, or of an order of magnitude or so, are most certainly not trivial. It only takes a handful of them to mount up to the difference between thousands and billions.

One such simplification was to treat the zircons as if they were isotropic — that is, that the diffusion happens at the same rate in every direction. Now zircons are anisotropic (for crystals geeks among you, they have a tetragonal lattice with a point group symmetry of 4/mmm and a unit cell of dimensions a=6.607Å, c=5.982Å), but at the time of the RATE project, the effect of their anisotropy on helium diffusion was unknown. However, a 2007 study by Reich et al (abstract) (full version) has since shown that diffusion rates between the different directions vary by up to five orders of magnitude at room temperature, and only become anywhere near isotropic at temperatures above 580°C. The abstract to Reich et al concludes with this advice:

These results suggest that the anisotropic nature of He diffusion at temperatures near the closure temperature should be considered in future diffusivity experiments. Furthermore, care should be taken when making geologic interpretations (e.g., exhumation rates, timing of cooling, etc.) from this thermochronometer until the effects of anisotropic diffusion on bulk ages and closure temperature estimates are better quantified.

Does it stand up under pressure?

Another simplifying assumption made by the RATE team was that diffusion rates would not be significantly affected by pressure. Again, at the time of the RATE project, the exact effects of pressure on helium diffusion rates in zircons had not been studied. In defence of this assumption, they pointed to some studies of argon diffusion in glasses, such as rhyolite obsidian, and gives some plausible-sounding, but nonetheless hand-waving, reasons why helium diffusion in zircons should be affected to a much lesser extent.

However, Kevin Henke, a geology professor from the University of Kentucky, responded to this claim by pointing to a study by Dunai and Roselieb (1996) that showed that at high pressures of 250 bars, helium would take tens to hundreds of millions of years even at high temperatures (700°C) to partially diffuse out of garnets. He also pointed out that garnets have much more in common with zircons, being "hard" silicate minerals, and consequently that this would be much more representative of zircons than rhyolite obsidian.

Did the RATE team stick to the scientific method?

On page 29 of the RATE project's report, we see this seemingly innocuous comment:

After consulting with Dr. Gentry, we have corrected, in the fourth column, two apparent typographical errors in the corresponding column of his table. One is in the units of the column (which should have been 10-9 cc/μg instead of 10-8 cc/μg); the other is in sample 4 of that column. The crucial fractions in column five were correctly reported, as we have confirmed with our data.

Kevin Henke asks this question about these corrections:

How and when were the "typos" related to the helium measurements (Q values) in Gentry et al. (1982a) discovered? Were the original laboratory notes consulted to correct the typographical errors? If not, how were they reliably corrected? Were the values corrected independently of any of Dr. Humphreys' results or were the values "corrected" to comply with Dr. Humphreys' results? (R. V. Gentry never replied to my emails on this issue.)

This is a very important question. One does not simply "correct typographic errors" in scientific results. The original lab notes would have to be consulted, independent evidence would need to be provided that these corrections really were warranted, and if the integrity of the data could not be established, the whole data set would have to be thrown out and the experiment re-done. In the absence of such independent confirmation, "correcting typographic errors" in this manner is an unacceptably sloppy shortcut. To their credit, they acknowledged that this was what they had done; if they had not done so, it would quite possibly have constituted scientific fraud.

How not to respond to peer review.

There have been several different critiques of the RATE team's helium diffusion experiments by subject matter experts, many of them evangelical Christians. Here are some of the key ones:

  • Gary Loechelt proposes a more realistic multi-diffusion domain model which shows that the measured values of Q/Q0 are consistent with the 1.5 billion year age of the zircons. He has also written a reply to the RATE team's response to his critique.
  • Kevin Henke provides the most detailed and thorough critique of the RATE project's claims. His tone is scathing at times, and he does spoil it somewhat by attacking their religious presuppositions, but many of his points are valid ones that do need to be addressed.
  • Timothy Christman points to other studies of helium diffusion in zircons which give completely different results from the RATE team's findings.
  • Rodney Whitefield points out further ways in which the data reported by the RATE team does not support their conclusions of excess helium.

Russell Humphreys responded to the critiques of the RATE team's research in an article on trueorigin.org in April 2005, another article on trueorigin.org on January 5, 2006, and again in an article on creation.com in November 2008. Gary Loechelt replied to these responses in April 2009, and Henke's latest revision of his critique, which also addresses the RATE team's responses, is dated June 20, 2010. I am not aware of any later responses from the RATE team.

In his 2005 response, Dr Humphreys made the following observations:

The first thing to notice about Henke’s issues is how few of them there really are.  For example, of the fifteen items above, six of them (4, 5, 6, 8, 9, 12) boil down to only one issue, how much helium was deposited in the zircons.  Several other items repeated themselves similarly.

The second thing to notice is how peripheral they are.  Not one of them has any chance of solving Henke’s real problem:  how to keep helium in leaky minerals for over a billion years.

Third, notice how petty most of them are. One of my challenges in answering those charges was to find different words describing their basic character: “molehill, not a mountain ... distinction without a difference ... haggling ... ridiculous quibble ... inconsequential ... majoring on minors ... irrelevant”. Eight of the items (1, 2, 3, 6, 7, 10, 11, 12) fall into that class.

Three points are of note here. First of all, it isn't clear how the six issues he cites as boiling down to one really do refer to the same issue. They may have the same end result in common, but they all refer to different errors in determining that end result. Furthermore, there are numerous other errors that he does not even attempt to address. Dr Henke's list of unanswered questions includes no less than sixty-six that are of a purely technical nature.

Secondly, Humphreys provides no calculations to prove that the objections really are as petty and inconsequential as he claims that they are. As we have seen from Reich et al and Dunai and Roselieb, pressure and anisotropy alone are sufficient to bring us right back from thousands to billions. In any case, even if the other objections really are "only a factor of two or so" or "only an order of magnitude or so," he needs to demonstrate that their cumulative effect really would still be as inconsequential and petty as just considering them individually.

Thirdly, anyone who has had any significant experience in science or technology will tell you that even seemingly "petty and inconsequential" mistakes can completely undermine the validity of your results. As a software developer, I get confronted with such examples several times a day. To dismiss critiques as "petty and inconsequential" in such a cavalier manner encourages Christians to adopt a sloppy and casual attitude towards science and technology -- and in many other areas of science, such an attitude can — and does — kill people.

No matter how "petty" and "inconsequential" you think it is, there are only three appropriate responses in science to a peer reviewer's criticisms. Either fix the problem, prove that it is as inconsequential as you think it is, or retract your claim. The RATE team's responses do none of these.

In any case, an error of ±2,000 years in a final result of 6,000 years is an error of 33%. This is an enormous error. It is far, far larger than anything seen in conventional radiometric dating, in which error bars can be tighter than one part in a thousand. Furthermore, it clearly does not account for the multiple "factors of two or so" or "an order of magnitude or so" for the simple reason that just one "factor of two or so" means an error of ±50%, which is one and a half times as large. Bearing in mind that we are dealing with extrordinary claims about accelerated nuclear decay that would easily qualify for a Nobel Prize if they had any merit, results with errors this large are simply far too weak to be credible.

Even if the study did have some merit, it is not at all clear how it supports the idea of accelerated nuclear decay in the first place. In fact, given the RATE team's own admission that accelerated nuclear decay would have generated massive quantities of heat, this would have expelled most if not all of the helium from the zircons anyway, and so the fact that we find any helium in zircons at all is pretty strong evidence against the RATE team's own model.

Since the RATE project, there have been numerous other studies of helium diffusion in zircons. As far as I am aware, none of them have confirmed the RATE team's findings. The figure of 6,000±2,000 years for the age of the zircons appears to be based more on miscalculation, circular reasoning, and improper data handling practices than on the actual age of the earth.

Featured image credit: James St John