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Intelligent Design, Creationism and Evolution in Denmark and the rest of the world

Radiometric Dating

It is often argued by creationists that radiometric dating methods doesn't work.
To support this Answers in Genesis has used dating of rocks from Mt St Helens' eruption.
Look here.

In short the article report that material from the eruption was dated by a well known lab, and dated to be more than a million years old, while it was in fact just a few decades old.
The conclusion in the article is, that this shows that the dating method doesn't work.

I have contacted the laboratory that made the dating, mentioned in the report, and confronted them with the claims that their datings support the idea that radiometric dating methods doesn't work.

Here is the answer:

Dear Mr. Frello,

Let me preface my remarks by saying that: 1) I am unable to comment on any work we may have done for a client.  I will limit my remarks to the data presented in the website.  2)  Geochron Laboratories has no affiliation with, nor does it endorse the work of, the Institute for Creation Research or that of any other so-called creation science or intelligent design organization.

As with any empirical analytical method, the potassium argon method for age determination of rocks relies on certain assumptions.  It is also limited in its accuracy by measurement uncertainties.  In the case of the classic K-Ar dating technique, it is assumed that the rock initially contains no argon except maybe some with an air-like isotope composition (i.e. it contains no so-called radiogenic argon 40), that the radioactive potassium 40 in the sample decays by a known and constant half-life process to Ar 40, and that the Ar 40 produced from this decay is fully retained by the rock until the measurement is made.  From these and other assumptions and from measurements of the actual potassium and radiogenic Ar 40 content of the rock, an age may be calculated estimating how long ago the rock was formed.

The first assumption, that the rock contains no radiogenic Ar 40 at the time of its formation, is not always completely true.  Rocks deposited in contact with much older rocks can pick up some of the argon 40 contained by the latter through diffusion at the high temperatures associated with their formation.  This can lead to rocks of apparently older age than their true age.  This can be particularly a problem with very young rocks (a few million years old is young by geologic standards), where such “excess” argon 40 can form a very large proportion of the total argon 40 in the rock.

The subjects of argon retention, diffusion and the introduction of "excess" argon have been widely studied in the legitimate scientific literature.  The subject is complex, but suffice it to say, it is very well known under what circumstances problems with radiometric dating can arise.  Methodologies for the analysis of very young volcanic rocks (less than a few million years old) have also improved over the last 30 years or so.  Some rocks are nonetheless problematic; not all samples can be reliably dated. If you wish to pursue this subject in more detail, look into the work of G. B. Dalrymple, a leading researcher in the area.  Some of his work is mentioned in these web pages:

Further, in the case of very young rocks (less than a few million years old), the uncertainties associated with the classic K-Ar measurement of very small quantities of argon 40 begin to rise rapidly.  This is especially true if there is any significant quantity of normal air argon in the sample as well, as is often the case.

The case described in the website of K-Ar dates of Mount St. Helens dome rock, assuming that the samples are in fact accurately represented, is an extreme case where the limitations of the methodology would be expected to be tested.  It would take only a small quantity of extraneous Ar 40 diffusing in from older host rocks to produce a non-zero positive age.  If this is what happened, then the apparent age should vary with potassium content of the rock fractions; the higher the potassium content, the lower the calculated age.  The whole rock and feldspar dates probably represent higher potassium content materials, while the amphibole and pyroxene components are likely very low in potassium content.  As can be seen, the former produce younger ages and the latter older ones.

The K-Ar method for age determination of rocks, when used for the dating of suitable materials, and with a recognition of the limitations of the method, is a reliable approach for determination of the very old age of many rocks.  The use of an extreme case at the expected limits of the method as a critique of the method as a whole is not justified, and in this case is likely disingenuous.

In my opinion, it is not generally worth the effort to engage Biblical literalists on these subjects, as they are often immune to reason and evidence.  They are typically not scientists in their approach to knowledge, but rather apologists and propagandists for a predetermined “truth”.  Some use the language of science to sound respectable, but much of what they say, when examined closely, is deceptive and a distortion of the actual state of modern science.

I hope that this explanation is clear.  Please let me know if I can provide you with any additional information.


Opdateret 27/09/2016