Rejecting Radiometric Dating: Isochrons

While making an exam, I needed to put a graph of an isochron plot for one of the questions. An isochron looks like this:

Note: the five data points for this measurement are all taken from different parts of the same sample. Originally, rocks will start out as a flat-line and as they age, the slope of the line increases. Here is a handy reference that walks you through how this process works:

This is a very powerful method that helps bypass one of the limitations of radiometric dating which is that if you have some of the daughter radioisotope present initially, you need to figure out how to subtract that out. Sometimes the background concentration will be relatively minor and will quickly be overwhelmed by the decay process. Some materials, like Zircon crystals, might night incorporate certain isotopes very well so you can have more confidence that any radionuclides present came from radiometric decay. But the clever part of the isochron method is that any extra of the daughter radionuclide simply shifts the y-intercept of the graph up or down, but cannot actually affect the slope from which the age is determined. So how does this fit into the Young Earth Creationist framework?

There are two approaches taken:

  • You can get isochrons by chance
  • Sometimes isochrons from different parent/daughter combos give discordant dates

Let’s focus on the 2nd one for now which when I searched for ‘Potassium-Argon Isochron’ 20 of the first 21 results were from YEC sites. That’s probably due to my internet search history. Thanks Google. So what graph did I see over and over… something like this:

The reason why this is supposed to be significant is this is from the Cardenas Lava Flow in the Grand Canyon which is dated to be closer to 1100 million years old using the more robust and less volatile Rubidium Strontium isochron method. However, whenever we try to use the Potassium Argon isochron method we find that the dates we get tend to be young… how can this be?? A simple explanation of course is that Argon is a noble gas and if the rocks were slightly heated, Argon would escape and the slope of the graph would decrease. However, Strontium is much less susceptible to slight heating and therefore more reliable.

An interesting, but not surprising observation

Note: it is an interesting question as to how specifically Argon was lost (see the section in this paper for a discussion on how we know the strata can be reliably dated to 1100 million years old and why Potassium Argon dates are lower titled ‘Cardenas Basalt Geochronology,’ but this helps demonstrate the absurdity of YEC science writing. It is to be expected and was known before Austin and Snelling measured the K-Ar isochrons that Argon is particularly volatile AND that this particular basalt gave dischordant results. But this was not surprising to non-YEC geologists because of the nature of Argon! So they did nothing new in their experiment other than try to cast doubt on the isochron method by assuming their isochrons were reliable measures of a rocks history.

A Good Opportunity to Correct Lies (note: see below for a discussion on the word lies) from Modern YEC Founder Henry Morris

Pevaquark note: the word ‘lies’ can imply deceit and I do not mean that he was intentionally deceptive. It is entirely possible that he didn’t realize that he was wrong in which case it was not intentional deception. However, Snelling & Austin should know better and stop reapeating such falsehoods

They had a perfectly good opportunity to help correct other lies that are told by YEC writers. Specifically, Henry Morris argued that three assumptions which cannot be known (except by someone who was there with the ability to measure beta particles or something):

  1. Constant process rate (or known functional variation of process rate).

  2. Closed process system (or known external effects on the open system).

  3. Initial process components known.

Specifically, the isochron method alone can help bypass the challenges of 2 or 3. Unfortunately, Snelling & Austin ignored the telltale signs of Argon leaking out in their data which are outlined by others like the blogger from Age of Rocks or the various papers discussing the formation like the one I cited above. And then, repeatedly throughout the paper they say things like:

There is a significantly non-zero 40Ar value for zero 40K, which would appear to refute the zero 40Ar* assumption of the model age technique.

That statement alone is shocking and very misleading and plays right into Morris’ 3rd lie. One of the entire points of the isochron or other methods is that by using a reference non-radiometric isotope, you don’t need to know the initial concentration of the daughter radionuclide!! It will only shift the graph up or down but won’t actually change the slope. There is Argon in the atmosphere… so no geologist would ever just ‘assume’ there’s none present at the start. That’s ridiculous and it would be wonderful if I never heard that statement again from YEC. Let me just say it in bold: you don’t need to know the original concentration of the daughter radionuclide to obtain accurate radiometric dates. There are methods, like the isochron method which they could have taught some good science or even corrected some lies of YECism, but they failed to do that despite knowing better as geologists.

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Dear Pevaquark

  1. You are a moderator on this forum. Nevertheless you use the word ‘lie’ several times in your post, to attack people that do not share your opinion. This is in contradiction with the guidelines of this forum for ‘gracious dialogue’. You should be debarred from your position as moderator.
  2. You tell us that five data points of the presented K/Ca isochron are the result of the measurement of the ratio of two isotopes in five different parts of the same sample. Why don’t these measurements all produce the same datapoint? Or were the samples taken from rocks that were miles away from each other, but are assumed to be produced under the same initial conditions and circumstances?

@WilliamDJ you need to work on your reading comprehension.

They do. The age of the sample is determined by the slope of the line generated. Not the individual data points which all lie on the same line.

I’m the gracelessest of them all, but @WilliamDJ has a point guys. The ell word w.r.t. Morris is not appropriate. Lying for the truth is OK :slight_smile: and convincing oneself that one isn’t is second nature. To us all. We have widely varying epistemologies, in our righteous, minds after all.

We do need to be gracious, and to be truthful, I struggle with whether to call out some statements as lies at times. If someone is presenting a point as a fact with full knowledge that it is not true, there is really no other word to describe that action, regardless of motivation. On the other hand, if you think something true that is not, it is not a lie, just ignorance. I think trained professionals with understanding of a discipline have a higher standard to meet when they present such information than a lay person following the conversation. However, it gets complicated on a forum like this. Basically, the bottom line is we have to show each other some grace, without compromising truth. That is hard.


IMO, “misrepresentation” is better than “the ell word.” It neither implies malicious motive nor excludes it.



I will leave the decision of editing the words up to a private discussion between the moderators. I hear and respect everyone’s sensitivity to the “L word” claim.

However, I do not support any character gutting of @pevaquark’s contributions to the Forum, especially when he is not participating as a moderator in this instance.

Can’t we just appreciate that this is the most scientific post we’ve had here in awhile? :rofl:


That is true, and I love it when I read a post and learn something new or gain a richer understanding, as I did in this case. I have a basic working knowledge of radiometric dating, but how knowledge of isochron methods can make results clearer was new to me.


Thanks William. I’m not attacking any people but statements they make. The statements are not true, false, lies, etc. I meant it in the colloquial sense that one can say statements that are lies without intentionally lying.

Ultimately, I’m not sure what’s worse- the founder of modern YECism not bothering to learn what he’s talking about which has been repeatedly ad naeusem by well meaning Christians and even YEC geologists who should know better… Or him just intentionally crafting misleading statements.

This reminds me of some blog posts from a decade plus ago by @sfmatheson:

It’s a good question and the answer is simply because there are many different minerals in various types of rock that incorporate the parent and daughter radionuclides differently. The first HyperPhysics link walks through how it works.


Omphaloi. To test our faith. It’s all belly buttons.

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The conversation in this thread about the ell word shows wisdom and generosity, unsurprising given the people involved. @pevaquark shared some of my thoughts on this dilemma, from years ago, and I hope we can all agree that the questions are not simple.

There is just one thing I would add: it is inaccurate, and misleading IMO, to refer to the discussion as a disagreement about “opinion.” The whole reason we have to discuss words and concepts like the ell word is the fact that falsehoods were spoken/written, and repeated after they were shown to be false. If there is an “opinion” under consideration here, it is the “opinion” that public figures (or any other humans for that matter) should endeavor to speak accurately and that they should admit error and correct it when appropriate.


You need to realise a couple of important things here, William. First, @pevaquark is not talking about people who don’t share his opinions. He is talking about people who aren’t getting their facts straight. Facts are not opinions. They are exactly the same for everyone, whether you are Ken Ham or Richard Dawkins, Donald Trump or Jeremy Corbyn, the Dalai Lama or the Pope. What geochronologists do, the measurement techniques that they use, the results that they get from those techniques, the assumptions that they do or do not make, and the tests that they have for any assumptions that they do make, are not opinions; they are facts.

Second, Henry Morris set himself up as a teacher in subjects such as geology and geochronology. James 3:1 tells us that teachers will be judged more strictly and as such they need to be held to higher standards. This is because anyone who teaches within the Church in any capacity is in a position of trust, and as such they must take extra care to make sure that the information that they are presenting is honest, factually accurate, and up to date, because to fail to do so is a breach of trust. A layman who gave up on compulsory science education at age sixteen and hasn’t set foot in a laboratory since can plead ignorance when they are told that they are not getting their facts straight. Teachers, pastors, and trained scientists do not have the luxury of that excuse.

The bottom line: if you don’t want to be accused of lying, don’t tell lies.


Very brave James. As Arthur Scargill said when the BBC tried to confront him with facts over the '83 UK miners strike which he led, ‘My facts are…’.

So… I’m kinda late to the party on this, as I’ve only recently come across BioLogos and I’m pumped to dive in!

@pevaquark, where could I find a ELI5 breakdown of what you posted above?


Welcome to the forum! It can be quite addictive, so watch out. :wink:

If you want to date a rock you are trying to measure the ratios of different isotopes in the rock. It turns out that rocks are often made up of many different minerals that incorporate different elements differently. Here is for example an isochron labeling different minerals within the rock as a whole:

The HyperPhysics link I posted above walks through the process, but basically when a rock first cools it is made up of many different minerals which incorporate different elements differently. So if you were to ask, what’s the concentration of Rubidium-87 it would be different in different portions of the same sample due to how elements with a +1 overall charge incorporate into the sample. However, one thing that will be constant is the amount of Strontium-87 vs. Strontium-86 in the rock originally. That is because there is very little difference chemically between the two radioisotopes besides a non-interacting neutron. And this is why isochrons all start out as straight lines. Over time, the Rubidium-87 will decay into Strontium-87 and each mineral within the rock will accumulate more Strontium-87. This effectively takes the original data points and shifts them left (meaning a loss of Rb-87) and up (since the Rb-87 becomes Sr-87). Something like this:

This is a powerful technique because it does not depend on the original concentration of the parent or daughter radioisotope and is one of the various ways that scientists can account for the “impossible problem” of Henry Morris which was (and is oft repeated) of how you need to know the amount of the radionuclides when the rock was formed… and since you weren’t there, but God was, all of radiometric dating is wrong!

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I THINK I’m following the science here, but want to be sure.

So what you’re saying is there’s a fixed amount of W Strontium-86 in rock, with X Rubidium-87 and Y Strontium-87. X decays into Y. The amount of Y can be measured against W, which exists independently of any other Parent-Daughter elements? And that ratio gives us an accurate age of the rock in question?

Is that close?

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Specifically, it’s usually a ratio of Rubidium-87 to Strontium-86 on the X-axis and a ratio of Strontium-87 to Strontium-86 on the Y-axis.

W is not produced by any radiometric decay processes.

Specifically, an isochron gives us the ratio for many minerals contained within the same rock. When you plot them out they lie on a straight line (assuming no contamination, loss of sample, etc.). The greater the age, the greater the slope and thus the slope of the line gives you the age.

Yes :grinning:

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WELL HOT DOG!!! That’s awesome, man. What’s even more awesome is I actually understood it (kinda)!!

THANK YOU!! Just knowing that Sr-86 exists as a constant in samples is big news, and this whole isochron business readily explains AiG’s bone they pick against K-Ar.

I appreciate it, Matthew. Thanks again, sir!


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