Isochron rock dating is fatally flawed

[npetreley]

Or so says this interesting article.

http://tccsa.freeservers.com/articles/isochrons2.html

The whole-rock isochron is justified on the basis that migration of the isotopes in a metamorphic event may be confined to distances of perhaps 1 cm. This is much larger than the average crystal size. Thus the original constituents of each crystal will lie nearby. By taking samples of 100-cm dimensions, one could assure that the entire content of the original crystals are well represented by the sample, with very small error. However, this matrix is the original melt that was theorized to be homogeneous. The ability to find differences in the rubidium content among the samples violates the assumption of original homogeneity. Original inhomogeneity is the only possible explanation: in other words, mixing.

This method of justifying the whole-rock isochron on the basis of the mineral is logically unsound. Within the larger matrix the tiny crystals may incorporate discrete trace elements and return them over time. But they are powerless to alter the composition of the whole-rock matrix.

[...]

The ability to obtain a whole-rock diagram, straight-line or not, can be considered proof that the data represent a "mixing line" rather than an "isochron". If mixing has not occurred, and the system has remained closed, then the whole-rock data must all lie on a single point. In fact, even if the whole-rock data show scatter, either mixing is indicated -- but of a complex nature, with more than two components -- or there have been subsequent alterations described as the system being open, or both.

Has any legitimate isochron ever been formed? It is improbable. There is ample evidence for mixing. Any "isochron" could be mixing. There is no way to rule it out. All whole-rock "isochrons" are mixing, and they are approximately 90% of all published. Many of the remaining (mineral) "isochrons" have a whole-rock point located close enough to the straight line to discredit them. Why should we expect any of the others to be "true isochrons", since mixing has the strongest probability?

 

[Jerry Smith]

Incredibly interesting article, if wordy. I can accomplish a summary of the article that I doubt anyone on this board will disagree with:

Isochron dating methods can fail due to undetected mixing.

Having gotten that out of the way, we can continue to have very high confidence in isochron dating methods.

The details of why can already be found in http://www.talkorigins.org/faqs/isochron-dating.html

which has already been posted here by LiveFreeOrDie, and which recognizes and addresses the potential for this specific problem with isochron dating methods.

The fact that creationists will go to such extremes to produce arguments about how radiometric dating can produce spurious results, having full knowledge that the problems are minor and the solutions are known speaks to the honesty of the William Overn's of the world. Overn has obviously been trained well enough in the science to understand the problems - surely he has run across the solutions before.

It is also possible to obtain an isochron with colinear data, whose age has no significance whatsoever. The only reasonably common way is by mixing of materials.
[...]
Mixing would appear to be a pernicious problem. Since A and B can be completely unrelated to each other, their individual compositions could plot to a fairly wide range of locations on the graph. The line AB could have any slope at all.

That fact also allows us to make a rough estimate of the percentage of isochrons that give colinear plots due to mixing. "Meaningful" (or "valid") isochrons must have a zero or positive slope; "mixing" isochrons can have any slope. If isochrons of negative slope (which must be mixing lines) were reasonably common, then we might suspect mixing to be an explanation for a significant fraction of all apparently valid "old" isochrons as well. That is not the case, however.

In addition, there is a relatively simple test which can detect mixing in most cases. The test is a plot with the same Y-axis as the isochron plot, but an X-axis of the reciprocal of total daughter element (D + Di).

then

Finally, and most importantly... if it were the case that isochron ages were essentially random, fictitious numbers, then we would not expect any sort of agreement between different methods, results published by different researchers, etc. For example, see the tables of meteorite isotope ages in The talk.origins Age of the Earth FAQ. Several different investigators using several different dating methods consistently produce concordant results.
This is easily explained (indeed, required) if these methods yield accurate ages. How is it explained if the "ages" are essentially random numbers? Suppose that the first researcher publishes an age of X years. Do you think that the next person to study the same formation is going to keep repeating the isochron method until obtaining isochron data that both plot as a line and agree with the original researcher's work? It's not his problem if the originally published age is incorrect.

 

[Zadok]

There ARE other methods too. As I posted in my FOSSIL FAQ (Which got almost NO notice, thank you very much!)-

*Dating fossils can be done in multiple ways.

Superposition of sedimentary rocks indicates their releative ages. In undisturbed sections, younger rocks overlie older.
Stratigraphic Correlation of strata in one place with those of the same age, deposited at the same period of time in another place, is fundamental in the interpritation of geologic history.
Fossils themselves are important in correlation of sedimentary rocks. The absolute age of rocks is accurately determined by the use of radioisotope dating. It is true that the relative ages of strata were determined prior to the development of radiometric dating, but radiometric dating has confirmed these relative dates to be correct. (i.e. index fossils)
Rock Facies , the sum total of the characteristics of a rock's despositional envirionment, are independant of geological time. An awarness of them, however, is important in correlation.
(1)Lithological Correlation uses the similarity of minerology, sorting, structure, bedding, sequence, and other similar features as indications of similar ages of rocks. Limited use though...
Standard Geologic Column which has been built up by combining rock sequences from different areas, can be matched with a time scale based on measured absolute ages of rocks.
(1)Geophysical Correlation makes use of similarity of physical rock properties as an indication of similar age. limited use though...
Rock Systems in the geologic column are major divisions of rocks deposited during a particular period of geologic time.

(1)Lithographical Correlation is of limited value, since rocks of different lithology often are deposited at the same time in an adjacent area. Geophysical Correlation is limited by the same factors of Lithographical Correlation.

*The accuracy of the empirical basis of the "geologic column" is daily re-confirmed by its use in the petroleum industry to actually produce tangible results. Since the existence of a given layer in the geologic column depends on a location being submerged during the corresponding time period, and the layer not subsequently being eroded away, it is not surprising that any given location would have only a limited number of layers. Thus, the the column as a whole is constructed from data from many locations. Nevertheless, there are locations which contain layers representative of all major periods in the last 500 million years. Furthermore, radiodating confirms the validity of the column.

 

[Jerry Smith]

Zadock - thanks... Needless to say, Nick's Tunnel vision will allow him to focus only on the specific short-comings of one of these methods at a time. He will likely never notice that one method's short-comings are answered by another method's reliability in the same area, making independent cross-checks possible that provide great reason for confidence in the dating of fossil finds.

Cross checking only works in Nick's mind if every method used is guaranteed accurate to begin with. He probably wonders why we do cross-checking at all, since he appears to believe that we all think there is no room for error in our dating methods.

 

[seebs]

Indeed, the cross-checking is what makes this interesting; observing that you can consistently get agreement between three of four methods applicable to a given sample, and that the sample has characteristics suggesting that the fourth method wouldn't work well on it... that's pretty good data.

 

[Zadok]

Cross checking only works in Nick's mind if every method used is guaranteed accurate to begin with. He probably wonders why we do cross-checking at all, since he appears to believe that we all think there is no room for error in our dating methods.

Typical eh?

I just got home from one of the bookstores down town, and I purchased "Descent of Man, by charles Darwin, 2nd Edition September 1874". I thought this would be a classic edition to my collection of books on Geology, Paleontology, Fossils, and other assorted material, when my mother walks in, saw me with the book and said "This book is VILE!" where I relplied, "Rocks don't lie mother..." Then she promptly stated "Jesus will make you pay"...

I think I better move out while get my associates in science. I really don't think I can take much more fundamental extremism.... Sheesh...

 

[LiveFreeOrDie]

The fundamental problem with this article is that it is making an apples-to-oranges comparison. The homogeneity constraint on Rb/Sr dating refers to the two daughter isotopes 86Sr and 87Sr. There is NO requirement that the Rb/Sr ratios be homogeneous -- in fact some variation in Rb/Sr ratios is desired.

From:
http://www.geo.cornell.edu/geology/classes/Geo656/98notes/98Lecture06.pdf

A large range in Rb/Sr ratio is also not uncommon. It may occur in whole rock samples when the whole rocks represent various members of a comagmatic differentiation suite, or in mineral samples when both K- and Ca-bearing minerals are present.

The reason Rb/Sr ratios vary within a single rock sample is quite simple: Rb and Sr are different chemicals with different chemical properties. Slight variations in the chemical composition of the rocks can affect the Rb/Sr ratio. Differential rates of cooling can also affect the ratio. From the same document:

However, igneous differentiation tends to increase the Rb/Sr ratio because Sr is removed by fractional crystallization of plagioclase, while Rb remains in the melt.

Contrary to the creationist document, variations in Rb/Sr content within a rock are a good thing. Again, the reason is simple: if all whole rock samples yielded the same Rb/Sr ratio, the isochron plot would be a single point. Since no line can be plotted through a single point, no whole-rock age could be obtained (although one could still obtain a mineral isochron). The truth is that the larger the variance in the Rb/Sr ratios, the more accurate the isochron becomes because it increases the confidence of the line-fitting calculations.

So what about the 87Sr/86Sr ratio? How can we be confident that it is homogeneous?

Yet again, the answer is simple chemistry. Since the two isotopes are chemically identical, there are no chemical or thermal processes that are capable of altering the ratio in the initial sample. As long as the 87Sr/86Sr ratio was homogeneous in the original molten rock (and there is no known mechanism for this to not be the case), then the two isotopes of Sr will be taken up at the same homogeneous ratio as the minerals crystallize.

The creationists' rejection of isochron dating seems to rest on this single conclusion:

All whole-rock "isochrons" are mixing...

As I have hopefully explained, whole-rock isochrons are an expected and desirable phenomena. This creationist argument has no merit.

 

[Late_Cretaceous]

"As I have hopefully explained, whole-rock isochrons are an expected and desirable phenomena. This creationist argument has no merit."

The thing is these creationists who "research" radiometric methods, with a mindset to debunk them, MUST come across this tidbit at some point. To miss it is due to either incompetence or a pathetic attempt to deceive thier intended audience.

 

[LiveFreeOrDie]

Because I am not a radiometric dating expert, I asked Prof. Joe Meert of the University of Florida to review the article Nick cited. Below are Prof. Meert's comments (italics in the quoted article by him).

Radiometric rock dating, the methodology of determining the date of formation of a rock sample by the well-established rate of decay of the isotopes contained, depends on accurately determination of the starting points, the original concentrations of the isotopes. Many methods of estimating these beginning concentrations have been proposed, but all rest on tenuous assumptions which have limited their acceptance. This paper attempts
to show that the Isochron-Diagram method contains a logical flaw that invalidates it. This most accepted of all methods has two variations, the mineral isochron and the whole-rock isochron. The logically-sound authenticating mechanism of the mineral isochron is applied to the whole-rock isochron, where it is invalid. The long-term stability of the whole-rock is applied to the mineral, where it is inappropriate.

When the isochron data are the result of the rock being a blend of two original species, the diagram is called a mixing line, having no time significance. This paper shows that all whole-rock isochrons are necessarily mixing lines. It is noted that by analogy the mixing-line logic casts strong suspicion on the mineral isochron as well. Since only whole-rock isochrons play a significant role in the dating game anyway, isotopic geochronology can be rather generally discredited.

JM: This is completely false. Overn is basically saying that since Rb-Sr whole rock dating has some problems, then all dating methods are suspect; yet, the concordance between various dating methods is itself a powerful argument for the effectiveness of radiometric dating. Furthermore, Overn plays a ‘bait and switch’ game throughout this paper to make his case.

Thanks mainly to the fact that they appear to be so constant, the decay rates of radioactive materials have become the primary mechanism for attempting to discover the age of rocks.[5,16] In addition to a constant rate of variation, however, any timing mechanism must also have a calibrated beginning point. A number of methods have been tried to calibrate the "radiometric clock". But they have all required unprovable and apparently unwarranted assumptions. Faure, in his textbook [9] refers to all of them as "assumed values" except for those obtained by the "isochron", or similar linear method.

JM: What exactly is a constant rate of variation as applied to radioactivity? I believe a ‘constant rate of decay’ is a more apropos term. The word ‘unprovable’ is also used here in the emotive sense. Proof in science means beyond a reasonable doubt. Overn uses the word in an absolute sense meaning 100% true. It is important to note syntax in an argument, since it is being used here to discredit radiometric dating.

The linear methods are several, and have in common the reduction of the data to a set which can yield a straight-line plot. Many exceedingly detailed descriptions of these methods are available.[1,2,5,16] A summary description of the Rb-Sr isochron is included below.

Arndts and Overn alerted the creationist community to the fact that in spite of the mathematical rigor of the isochron, it also has unwarranted assumptions, and the data carefully gathered and processed to indicate immense ages can more appropriately be dismissed as indicating the recent mixing of two or more magmas.[1,2,3] Dalrymple[6] challenged our analysis with five points, all of which were promptly and thoroughly
refuted.[4]

JM: Arndts and Overn have not; however, published their criticism in the appropriate scientific literature. Why? Because they rely on a flawed argument and a bait-and-switch to support their argument.

In Dalrymple's latest book [7] he ignores the entire issue of the whole-rock isochron, only defending the mineral isochron. There is sound logic supporting the mineral isochron, but another fatal flaw. Individual mineral crystals are not closed systems. Even over the few thousands of years available in the young-earth paradigm, they are insufficiently stable to give acceptable data to the geochronologists.

JM: This is a statement of fact without evidentiary support. The behavior of different minerals with regard to their diffusion characteristics (e.g. closure) has been studied by a number of scientists (McDougall and Harrisson for a discussion of mineral diffusion in the Ar-Ar system; Dodson and McClelland Brown for Sm-Nd, Rb-Sr, U-Pb and fission track). Basically, the entire argument rests on Overn’s unsupported statement.

(some snipped by LFOD)

If all initial 87Sr-86Sr ratios in the system are assumed to be the same, the scheme can be made to work, as the unknowns are reduced to two, the common age, and the common strontium ratio. Any two samples may now introduce the required two equations, and any more beyond that will simply improve the accuracy and the confidence level. This assumption is outside the experience based on field data, however, where the general
case is that every sample has its own unique ratio. However, it can be rationally assumed that each sample we find has its own age and its particular rubidium concentration, which over time may have imparted a unique portion of daughter isotope. The assumed uniform strontium ratios should certainly be valid when applied to a rock system solidifying from a uniform homogenized melt. We must emphasize, however, that this enabling assumption must fail in the absence of an initial homogenized melt.

JM: Here is the beginning of the bait-and-switch. The distinction not made here is subtle, but important. Overn begins by talking about initial 87Sr-86Sr ratios and then concludes with the statement that the ‘rock system’ must solidify from a uniform homogenized melt. Geochronologists however refer to homogeneity of the melt with regard to Sr-initial ratio. The magma can be inhomogenous with respect to mineralogy and the rock types formed from the magma may be chemically distinct but share an initial common Sr-ratio. However, Overns discusses this a bit later and he could rightly accuse me at this point of nit-picking.

A "closed" system

If isotopes have migrated in or out of the sample during the aging period, the resulting data have no time significance.

JM: This is overstated. The issue is how much migration has occurred and whether or not this migration can be accounted for. In the case of the Rb-Sr system the migration will be evidenced by lack of straight-line relationship as noted by Overn below. In the case of U-Pb in zircon it will be shown by discordance and in the case of the K-Ar system, by the lack of a plateau age in the Ar-Ar variant or by discordance during stepwise release.

Isochrons are thought to be self checking in this regard, since with several samples an open system with random migration should scatter the points off of the straight line. Indeed, it often happens that there is a scatter of data, rendering the isochron worthless. But there are many occurrences of isochrons having acceptably straight-line form that are also rejected. Often "metamorphism" is cited as the probable cause, the system having opened, either partially or completely resetting the clock. [11,19] In order to assure an acceptably closed system, samples as large as 1 meter cubes have been suggested.[20] The assumption of a closed system for many of the isochrons, if they have not been questioned by the geochronologists, will not be challenged here. We note that these are generally obtained on the samples of larger dimensions, that is the whole-rock isochrons.

Independent equations

If the equations are not independent, the problem cannot be solved. This would be the case where all samples on the diagram plot on a single point. Although the single point on the diagram is valid, there is no way of finding a slope or intercept. If the melt were initially homogeneous and remained closed, it could be expected still to be homogeneous, and yield that single-point isochron. This should be the general case of the
whole-rock isochron.

JM: Definitions are important here. There is, by definition, no such thing as a single-point isochron. This also assumes something that the whole-rock method does not. The utility of the whole rock method requires a suite of co-genetic rocks that homogenized within a reservoir with respect to their original 87Sr/86Sr ratios. Fractional crystallization of the melt can lead to a suite of co-genetic rocks with varying amounts of Rb that will lead to a linear plot on an isochron diagram. We’ll see how Overn dismisses (without evidence) fractional crystallization later in the page.

The need is to find samples with a variety of initial rubidium content but still having initial strontium ratios that are known to be uniform. The assumed initial homogeneous melt cannot be expected to give whole-rock samples with variable rubidium, but the assumed uniform 87Sr-86Sr ratios demand such an initial homogeneous melt.

JM: Fractional crystallization is, indeed, one method capable of doing exactly what is called for above. I suspect this is why it is dismissed (out-of-hand) below.

The mineral isochron solves the dilemma. The mineral crystals have done the job in an elegant way. Crystals naturally form around a specific chemical composition, each atom occupying its naturally-assigned site. Foreign atoms just don't fit, either electrochemically or physically, and are strongly rejected. Depending on its concentration in the melt, a foreign element may have more or less acceptance in a crystal, based on its chemical and physical resemblance to one or another of the normal host elements. As the crystals form, each different mineral type accepts a different trace level of rubidium and of strontium. Because of their individual unique chemistry they each extract a different amount of rubidium and of strontium from the melt. The crystals of the individual minerals are used as the rock samples in the mineral isochrons.

JM: Syntax is important, minerals are used as mineral samples.

MIXING

Often an isochron yields an unacceptable slope, indicating an age much too young or much too old to be compatible with the accepted model. [19] Frequently the slope is negative.[18,14] A common explanation for these cases is "mixing". It has always been recognized that the same straight-line plot as the isochron can be achieved if the original melt were a mixture of two original homogenized pools.[12] Figure 1. may also be used
to illustrate this case. If points a and c are the compositions of the two original pools that partially merged to form the melt, any sample from the melt will occupy a place on a straight line between them, such as point b. No sample will be found above a or below c. Such a "mixing line" has no time significance, and the textbook warns to be wary of accepting such mixing as a true isochron.

JM: Yes, as noted by Overns mixing can produce a false isochron. This was, of course, discovered and discussed by conventional geologists at length and provides yet another excellent example of careful scholarship by geochronologists. In fact, were it not for the rigor of conventional science, it is likely that creationist’s would have no complaints! Geologists list the assumptions of a method and the drawbacks and pitfalls of the various radiometric dating methods. They also list the advantages, the utility and methods for double-checking the results for possible pitfalls. Creationists seize upon the pitfalls and fail to acknowledge the successes! This is not surprising for people who claim ABSOLUTE truth and have trouble accepting the tentative nature of science. But that is an aside, the real question is whether or not mixing invalidates all geochronologic results.

Faure's text also proposes a test for mixing. [13] If a plot of 87Sr-86Sr vs 1/Sr (the concentration of strontium) shows a linear relationship, then mixing is indicated. A brief study conducted in 1981 showed a high degree of correlation to this mixing test in the isochrons being published.[3] A subsequent public dialog between Dalrymple[6] and Arndts & Overn [4] concluded that although the mixing test is strongly indicative of
mixing, there are circumstances under which mixing would not be detected by such a test, and others wherein the test could give a false indication of mixing. The caution for the geochronologist would be to suspect any isochron, since there is no way to rule out mixing.

JM: Geologists SUSPECT everything! That is why the checks and balances are put in place. That is why care is taken in collecting the samples (noting field relationships that might offer independent evidence for mixing; thin section examination, studies of other isotopes within the rock sequence that may yield evidence of mixing etc).

It is now clear, however, that there is at least one positive test for mixing. It is the whole-rock isochron itself. If the whole rock yields samples that give a linear plot, whether the slope is positive or negative, or whether the slope signifies an age that fits a preconceived model or not, there is no other known mechanism outside of mixing to which the data may be rationally ascribed.

JM: This is wrong since fractional crystallization will yield exactly such a plot!

(Continued)

 

[LiveFreeOrDie]

(Continued from prior post)

Discussion

Mixing is an unfortunate misnomer that has become popular for describing rocks formed from two or more original melts, or from a melt becoming contaminated by isolated incorporation of local rock. Understand it to mean partial mixing, with resulting heterogeneity. Complete mixing would result in homogeneity, and would give only a single point to plot. No curve of any kind, nor even a scattering of points would occur.

JM: The bait and switch is extended. Note, that there is no more discussion here of Sr-initial ratios

This homogeneity is the assumed starting point in the history of the rock being dated. It then solidifies. But now, years later, we dig up 6 adjacent meter cubes of the rock, and discover that the normalized ratio of the parent (and incidentally of the daughter) is different in each cube, sufficient to plot as an "isochron". How can we rationally accept the assumed initial homogeneity? We can not.

JM: The bait and switch is further extended. They do not note that this is a hypothetical example for which they supply no data.

What is needed but missing in the whole rock isochron is a mechanism to establish initial homogeneity, and then to extract heterogeneous samples. The mineral crystals do the job in an elegant way. Each type accepts a different level of contamination of the parent isotope, chemically determined. One cannot rationally extend this process back to the whole rock. It has been tried, but there is a fallacy . [5,20]

JM: This is false, whole rock isochrons depend solely on initial homogeneity of 87Sr/86Sr ratios in the melt and thus can produce isochrons.

As we stated in 1986: [5]

The whole-rock isochron is justified on the basis that migration of the isotopes in a metamorphic event may be confined to distances of perhaps 1 cm. This is much larger than the average crystal size. Thus the original constituents of each crystal will lie nearby. By taking samples of 100-cm dimensions, one could assure that the entire content of the original crystals are well represented by the sample, with very small error. However,
this matrix is the original melt that was theorized to be homogeneous. The ability to find differences in the rubidium content among the samples violates the assumption of original homogeneity. Original inhomogeneity is the only possible explanation: in other words, mixing.

JM: Note that the author switches from magmatic systems to metamorphic systems? Metamorphic effects are much more difficult to accurately date with Rb-Sr (but it can be done). What’s important in dating metamorphic effects using Rb-Sr is to note the degree of metamorphism. All of this is, of course, a further bait-and-switch on the part of Overn. Rb-Sr dating of metamorphic events is an interesting topic, but irrelevant when talking about magmatic systems.

This method of justifying the whole-rock isochron on the basis of the mineral is logically unsound. Within the larger matrix the tiny crystals may incorporate discrete trace elements and return them over time. But they are powerless to alter the composition of the whole-rock matrix.

JM: This makes no sense. Whole rock isochrons are justified based on WR isochron methods.

It is claimed that fractional crystallization of magmas and separation of crystals from the remaining liquid result in suites of comagmatic rocks of differing composition. [10]. This may be true, but there is no experimental evidence that this can generally be applied to trace elements that are foreign to the crystals.

JM: It is true! In fact, as noted above this is the basis (among others) for the whole rock isochron method! Trace elements such as 87Sr 86Sr and 87Rb are incorporated into the minerals as Overn notes elsewhere. This is simply a convenient way to dismiss fractional crystallization without having to supply any data!

Add the fact that trace elements are not securely held by crystals until temperatures are well below the melting points, and this postulate falls far short of explaining the variation in rubidium in whole-rock isochrons. Mixing is much preferred, particularly when it is noted that many data sets have negative slope, where mixing is always the accepted explanation. Often the negative-slope data pertain to large formations that particularly fit the hypothesis of slow cooling from a melt. [15,18]

JM: You’ll have to show this. Presumably, the argument is made about closure temperatures of Rb-Sr in minerals. It is true that minerals close at different temps (as noted above), but if creationists want to use this argument, then they must admit to million-year cooling times for the rock bodies. If they will not concede this point, then the closure temperature argument is moot. The closure temperature differences contribute to the scatter around the isochron and are included in the age.

In the case of the mineral isochrons the scheme postulates an initial homogeneous melt, represented by a single point on the diagram.

JM: This is false as noted above. It is the 87Sr/86Sr ratio that is homogenized. In a suite of differentiated co-magmatic rocks, the whole rock isochron will produce a linear array.

As the crystals form, their differential solubility will move their individual points on the diagram horizontally , different distances. (Only horizontally, since the vertical is a ratio of two isotopes of the same element). The large volume of whole-rock isochrons, however, shows the general case to be an initial heterogeneous melt represented by the kind of diagram published as an isochron, and which we conclude is actually a mixing line. Any point in the melt can be represented as a point on the straight line. When mineral crystals form, each crystal will move its point off the straight line in one or the other horizontal directions. The result is a scattering of the points. The geochronologist discards it as one of the following:

A three or more part mixture,

Subsequent metamorphosis,

Not a closed system: In this case he recognizes that crystals really cannot be expected to be a closed system. They tend to continue to reject contaminants long after formation, the mobilities of foreign elements in crystals being a whole school of scientific study. The retention of trace elements in crystals is so inadequate that it has been possible to construct "Isochrons" from various parts of the same crystal.[17] It is common that when the mineral isochron fails, the geochronologist then produces a whole-rock isochron from the same formation.

The ability to obtain a whole-rock diagram, straight-line or not, can be considered proof that the data represent a "mixing line" rather than an "isochron". If mixing has not occurred, and the system has remained closed, then the whole-rock data must all lie on a single point. In fact, even if the whole-rock data show scatter, either mixing is indicated -- but of a complex nature, with more than two components -- or there have been
subsequent alterations described as the system being open, or both.

Has any legitimate isochron ever been formed? It is improbable. There is ample evidence for mixing. Any "isochron" could be mixing. There is no way to rule it out. All whole-rock "isochrons" are mixing, and they are approximately 90% of all published. Many of the remaining (mineral) "isochrons" have a whole-rock point located close enough to the straight line to discredit them. Why should we expect any of the others to be "true
isochrons", since mixing has the strongest probability?

JM: Statement of fact without evidence. Some false isochrons have been produced. As noted above, it was conventional science (not creationists) who brought this issue to the fore. Independent confirmation of WR-min Rb-Sr isochrons has shown the utility of the method.

If one possesses a strong faith in the antiquity of the rocks, one could rationally expect that an occasional mineral isochron is legitimate. But it would also require the whole-rock diagram to be concentrated in a single point. (Neither a straight line or scattered).

JM: This is false as noted above. It is the 87Sr/86Sr ratio that is homogenized. In a suite of differentiated co-magmatic rocks, the whole rock isochron will produce a linear array.

Often a whole rock point is put on a mineral diagram. That does not meet the criterion. Several whole-rock samples must be obtained, using the same techniques required for the whole-rock method. Their individual data points must be identical, i.e. superimposed on the diagram. At that point mixing would not have been ruled out, but all available tests requiring mixing would have been eliminated.

JM: Sure it does as it represents the single point within the sample.

In the dialog with Dalrymple [4] it was noted that he is unwilling to defend the whole-rock isochron.

JM: Dalrymple probably realizes (as do I) the futility of arguing a point with someone who is going to misrepresent the method anyway! Look, Rb-Sr whole rock isochrons are problematic in some cases, but in others they work quite well. Geologists have learned how to check and double check the methods to make sure they are not mixing lines and to demonstrate the comagmatic nature of the sequence. There are many examples of this in the literature (including this one http://gondwanaresearch.com/radiomet.htm)

 

[Jerry Smith]

Great post LFOD! Thanks!

 

[LiveFreeOrDie]

That's funny. This thread got awfully quiet all of a sudden.

 

[Jerry Smith]

I think it is a miracle. Isochron dating had a fatal flaw, but now it appears to be in remission.

"You will not have died in vain!"
"I'm not dead yet!"
"You will not have been mortally wounded in vain"
"Actually, I think I'm getting better.."

 

[DonaldW112]

Nick are you there? Any comments??

Also, Nick why don't you use "god did it" to explain bugs in your computer code?

 

[Sauron]

Sometimes there is justice, I guess. Live Free or Die has destroyed npetreley's arguments so badly that *nobody* is willing to try and defend them.

 

[randman]

Nah, LFOD is like talking to a brick wall most of the time so it gets boring.

 

[Sauron]

Originally posted by randman
Nah, LFOD is like talking to a brick wall most of the time so it gets boring.

But your complaint that LFOD is a "brick wall" doesn't apply here. LFOD only posted a response from an expert in the field, who shredded npetreley's claims.

LFOD wasn't even doing the arguing. So this isn't about LFOD at all; it's about the holes in npetreley's post.

Not surprised, you understand.

 

[DonaldW112]

Originally posted by Sauron
Sometimes there is justice, I guess. Live Free or Die has destroyed npetreley's arguments so badly that *nobody* is willing to try and defend them.

It sure seems that way!

 

[randman]

Do you mean LFOD's link to Talkorigins. Personally, I don't even bother with anyone that links to that site. If I wanted to hear spin from the likes of Carville, I'd watch Crossfire.

 

[Sauron]

Originally posted by randman
Do you mean LFOD's link to Talkorigins.

No, I meant the letter that he sent to Professor Joe Meert. You know - the one where the Prof. systematically addressed the specific errors in the article that Nick was so proud of?

Personally, I don't even bother with anyone that links to that site. If I wanted to hear spin from the likes of Carville, I'd watch Crossfire.

Yeah, so I've heard.

But as I said before: for all your noise and bluster, you have yet to refute the data at talk.origins.

One more time: *disliking* an argument is not the same as refuting it.