Understanding how measurement works (with reference to radiometric dating)

Continuing the discussion from Some kind of waterfall that quickly fossilized teddy bears:

Yes Craig, I will help you. You need to understand the basic principles of how measurement works before you try to discuss the reliability or otherwise of radiometric dating. Allow me to explain a couple of important facts to you.

1. Unreliability is always quantified.

You said:

That is a straw man. Nobody is claiming that the assumptions behind radiometric dating are always correct. No form of measurement of any kind works like that. Every form of measurement has potential sources of error, even the tape measure that I used today to measure my desk. But – and it is a big but – there is a massive difference between “occasionally out by a few percent” and “consistently out by a factor of a million.”

In every area of science, researchers are required to identify, catalogue, quantify, and account for all possible sources of error. This means that, among other things, they have to determine the maximum extent to which their assumptions could have been violated. Geochronologists are fully aware that there could be contamination or leakage. But they take steps to figure out exactly how much contamination or leakage there could have been, and what effect it could have had on the overall result. So when they tell us that the Earth is 4.54±0.05 billion years old, we can be confident that they have taken these uncertainties into account.

Scientists generally divide sources of error into two categories: random errors and systematic errors. Random errors represent the “spread” of a number of measurements of the same thing around an average value, and that is what is represented by the error bars. Systematic errors represent an offset from zero that applies to all measurements across the board in this particular case.

Your Novarupta example, assuming that it was collected and processed correctly, is an example of a systematic error. It indicates that that particular method might overestimate ages by up to 5.5 million years. This means that Precambrian rocks dated by the same method to 550 million years could be as young as 544.5 million years or possibly at a stretch 540 million years. It does not justify claims that they could be as young as six thousand. You CANNOT claim that a measurement technique is significantly more unreliable than what is indicated by the random and systematic errors.

2. Unreliability is specific.

Another thing you need to understand is that radiometric dating is not just one single technique, but a whole range of related techniques. There are about forty different isotopes used in radiometric dating, from carbon-14 through to uranium/thorium/lead via potassium-argon and rubidium-strontium. Each of these will have different considerations, different preconditions, different chemical and physical properties, and different subtleties. There are also dozens of different minerals that may or may not be able to be dated radiometrically. Some of them will be more reliable than others. Some of them may overestimate ages if their assumptions are not met, but others may underestimate them.

This means that you have to consider each different case individually. You cannot make any blanket claims that radiometric dating as a whole is “unreliable” just because some methods give flaky results on some minerals. K-Ar dating may give flaky results due to the fact that argon is a gas and more likely to leak out or be trapped in lava as it solidifies, but that tells us nothing whatsoever about the reliability of U-Pb dating of zircon crystals.

This is a point that I keep having to make over and over again in response to young Earth claims, Craig. It is one thing to show that some methods give errors of up to a few million years on some minerals under some circumstances. It is a completely different matter to show that all methods are consistently overestimating ages by up to a few billion years – a thousand times as much – in every circumstance. Such a leap is simply not justified. There is nothing “evolutionist” or “biased” about me saying so – that is simply how measurement works in every area of science.


Keep in mind also that there are several different assumptions involved in radiometric dating. Any claim involves assumptions; it is ridiculous and hypocritical but sadly not unknown to pretend that “it’s based on assumptions” is a valid critique of something. Radiometric dating, like any science, involves basic philosophical and ethical assumptions like “you should be honest in your reporting of results”; “it is possible to meaningfully observe the world around us”; “the world behaves in reasonably consistent ways”, etc. Those assumptions can be justified by biblical considerations, as well as in various other worldviews.

Radiometric dating also assumes that the laws of physics governing radioactive decay have not changed. This is not a blind assumption. First, these laws are very fundamental parts of physics; any significant changes to them would prevent atoms from existing. Second, we can look at evidence of patterns in radioactive decay from the past and see that they match modern observations. For example, the half-lives of elements observed in a distant supernova match what is measured in the lab today. Although various scenarios of speeding up radiometric decay have some popularity in young-earth circles, they all imply the production of enough radiation to kill all life, producing enough heat to vaporize the earth, causing all atoms to fall apart, and other side effects that cannot be reconciled with the biblical account nor with other evidences of history. It is possible to speed up certain nuclear reactions, but nuclear reactors and nuclear bombs tend to leave noticeable traces. (Electron capture radioactive decay is affected by the chemical bonds of the atom in question, but this is neither a huge effect nor a type of radioactive decay used for age dating.)

What does require some effort to confirm is the available evidence relating to the original and current amounts of the parent and daughter isotopes. Each system has particular factors to measure and conditions where it may or may not work so well. But these issues are well-documented. Proper use of the techniques will raise red flags where there are potential problems. Carbon-14 is by far the easiest one to have problems with. Although it is extremely useful, it is far easier to contaminate than any radiometric dating method that applies to igneous rocks.


It is also biblically supported.

This is what the LORD says: If I have not established my covenant with the day and the night and the fixed laws of heaven and earth…
Jeremiah 33:25

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This point can’t be emphasised strongly enough. YECs view assumptions as a get-out-of-jail-free card that lets them hand-wave away anything and everything about science that they don’t like. It’s important to hammer home to them that they aren’t.

In order to challenge a scientific method by attacking its assumptions, there are three things that one must do:

  1. State precisely what the assumptions are.
  2. Make sure that the method really does make the assumptions that you’re claiming, and that it hasn’t been superseded by a more modern method that does not. (Example: isochron dating.)
  3. Provide evidence that the assumptions that it does make are not just wrong, but sufficiently wrong to accommodate your alternative hypothesis.

Most young Earth arguments don’t get any further than point 2, if that. I’m yet to see a single young Earth claim that comes anywhere close to adequately addressing point 3.


A fourth consideration for assumptions is checking to see if the person shouting “assumptions” is making the same assumption.

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James, I really hope I get the chance to buy you a drink someday.

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@jammycakes, @paleomalacologist , thanks for your detailed, clear explanations. These topics are out of my areas of study, but I hear dating methods harranged by people who have memorized some YEC script, but who can’t possibly know what they are talking about. And the Assumptions Card. It wins every time, when the debate opponent doesn’t have the education or the right script. Thanks!

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Hopefully this will pre-empt a vulnerable reader going down the rabbit hole, but of course it can’t reason anyone out of the warren as they didn’t get there by reason.

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