@PaulGiem reached out to me discuss a thread on the forum from a while ago (Paul Giem: Isochron or mixing line?) that references his work (https://scientifictheology.us/wp-content/uploads/2020/12/IsochronDating.pdf). The original conversation involved @Ignostic and @davidson.
To follow this conversation, you learn a bit isochron data, one advanced radiometric dating technique that geologist date rocks. This is a powerful method because requires fewer assumptions that other methods, and works by measuring a precise pattern (an upward sloping line) in several samples.
Basically the slope of the line corresponds to the age of the rocks. Several samples of rock are drawn, and that is what forms the line.
Mixing Can Produce Isochrons Independent of Age?
Giem’s idea is that mixing could produce a line in these plots, and it is notable that this is stated by Davis Young too.
Conceivably, straight lines on an isochron diagram could be generated simply by mixing two magmas in various proportions and allowing them to crystallize. If so, the resulting straight line would tell us nothing about the age of the rocks.
So his basic idea seems plausible. Davis goes on to point out the problems with this:
The vast majority of straight lines of an isochron plot, however, cannot be explained by simple
mixing for several reasons. We mention only two. For example, evidence of extensive magma mixing can generally be detected from variations in chemical composition of an igneous rock body as well as from field evidence. For most igneous rock bodies, however, field and chemical evidence of significant mixing of two or more magmas is lacking. In addition, the mixing hypothesis fails to account for the very wide range of values of Sr isotope ratios that have been observed on all isochron diagrams of igneous
That might be true, but it seems to be difficult to show that data to us in a way we can see it. I think an objection @Ignostic found was more directly visible:
From this discussion, I am still wondering how geologists constrain and quantify the uncertainty of dating from isochrons due to this mechanisms. Perhaps it doesn’t make space for a YEC earth, but it might mean that some of the confidences are overestimated. Perhaps.
Paul Giem’s Email
Today Paul sent me a very courteous email noting he had missed the discussion on this. I offered to create this protected thread for him to hash this out with informed and respectful scientists. Here are the key parts his email…
Perhaps what I consider the biggest misunderstanding of the paper in the comments was the implication that I was simply looking for a way out of accepting radiometric dates at face value, as in
“As far as the particular work of Giem goes, it represents one of myriad “just so” stories that essentially say “but what about THIS for undermining confidence in dating?””
That is a fair point, and I think we should hear him out.
As noted by Gunter Faure, mixing lines can (and 2-component mixing lines always do) precisely mimic isochrons, and as I mentioned in the paper, I don’t like the idea of people staring at each other across an unbridgeable chasm, with no testable way to resolve their differences. My model for flattening mixing lines simultaneously was not meant to simply say that there was a possible way to explain matching apparent isochrons, but rather to create a theoretical model for creating matching mixing lines so that we could test whether those apparent isochrons are really isochrons or are better explained as mixing lines. In other words, it was created to be tested.
I think that if we are to be good scientists, we cannot start with the assumption that short age, or long age, is correct for any given feature of nature. We may get there eventually, but as soon as we assume our conclusion, we have short-circuited the process. (That position makes me a heretic among some young life creationists.) I would appreciate criticism of the theory, or perhaps the testing of it on data, with confirmation or refutation of the theory that a particular suite of matching apparent isochrons can be explained by mixing lines.
That, it seems, is the goal of this thread. To be honest, I’m not even sure what Paul thinks about the age of the earth from this email. It is the sort of email I would expect from a secular scientist that was exploring the reliability of a particular method.
This thread is protected. @Moderators will watch it more closely.
Disrespectful and uninformed posts will be deleted. Please engage with Paul respectfully and on topic, noting as well that he works a full time job and may be delayed in some answers.