Hello all.
Before addressing your specific objections (which I will hopefully get to this weekend), I would like to provide an example of how geochronology is applied in practice. The radiometric study to be analyzed is related to Rb-Sr Isotopic Systematics of the Lherzolithic Shergottite Lew88516 by Borg et al. The study can be found
here.
The opening paragraph makes a forceful statement that is typical of geochronological studies, as well as uniformitarians/evolutionists:
quote:
Our analyses yield a crystallization age of 183 10 Ma and an initial 87Sr/86Sr ratio of 0.710518 60. This age agrees well with the ~170 Ma age previously determined for LEW by the U-Th-Pb method by [5] and with the Rb-Sr age of 187 12 Ma determined on ALH by [6], but is older than the 154 6 Ma Rb-Sr age determined on ALH by [7]. (p. 1)
Here we see that two different dating methods applied by 4 different studies yielded ages concordant with the expectations of geochronologists. On the surface, this appears to be an outright victory for radiometric dating. We shall soon see, however, that this apparent victory is no such thing, but is instead a superficial camouflage veiling a mountain of rationalizations invoked for the sole purpose of explaining away contradictory data as mere coincidence.
The two lines of contradictory evidence in this study are the following: (1) Isochron-yielding leachates producing an age of approximately 726 million years (discordant by about 400%); (2) Four separate mineral separate/leachate pairs yielding an age of approximately 90 million years (discordant by -50%).
Borg et al recognize the discordant isochron and plot it in Figure 1. They write:
quote:
Note that the leachates fall to the left of the mineral isochron and with the exception of Px (L) define a line with a slope corresponding to an age of about 726 287 Ma. (p. 1)
The geochronologists attempt an explanation for the discordant isochron:
quote:
The Rb-Sr isotopic systematics of the leachates are consistent with Rb removal and Rb/Sr fractionation from the host mineral fractions at ~90 Ma. This fractionation may be associated with secondary alteration or shock metamorphism. (p. 1)
They justify their explanation as follows:
quote:
Several petrographic features of the lherzolitic shergottites underscore potential problems with the isotopic analyses of these rocks and emphasize the need for very careful mineral separations. Shock features are ubiquitous throughout the lherzolitic shergottites and include the presence of maskelynite, mosaicism of olivine and pyroxene, and the presence of shock melts [2,7]. Shock melts are likely to have been re-equilibrated with the bulk rock at the time of the shock event [7] and therefore may have incorporated secondary alteration products that are not in isotopic equilibrium with LEW mineral separates. Thus, shock melts should be excluded from the mineral separates. An additional potential problem arises from the fact that the olivine compositions are too Fe-rich to be in equilibrium with the pyroxenes. The disequilibrium between olivine and pyroxene in the lherzolitic shergottites has been attributed to crystallization from different source liquids [7] and to nearsolidus re-equilibration of the olivine in a closed system [1,9]. Obviously, xenocrystic olivine is not expected to lie on the isochron defined by the other phases and would have to be excluded from the age calculation. (p. 1)
As is clearly seen, the geochronologist is sure to begin his experiment with rationalizations at hand, just in case. They proved to be of great value for this study in particular, because they were used to explain away samples Mask(L), Wr-2(L), Oliv(L), Mg-Px(L), and Fe-Px(L), which formed a very neat isochron that contradicted geochronological expectations. Such a distillation process is invoked frequently by geochronologists to easily discard non-preferable ages. If there is a scatter of unwelcome dates, the typical invocations of alteration, open system behavior, or re-heating events are deployed at a moment’s notice. If the unwelcome dates, however, form an isochron (a very common occurrence, as evidenced by the fact that it took me no more than 5 minutes on-line to find such an incident), then much more imaginative hypothetical geologic events are to be concocted. Hence, the references to secondary alteration and shock metamorphism (p. 1) by Borg et al, which can somehow magically produce analytically precise isochrons with no geologic significance whatsoever.
But the dubious nature of such explanations doesn’t end there, as is evidenced by the following statements:
quote:
Rb-Sr isotopic analysis of maskelynite, whole rock, olivine, and pyroxene fractions from LEW yield a crystallization age of 183 10 Ma. Despite the fact that there is some scatter in the data, all of the analyzed mineral fractions lie on the isochron. This is somewhat surprising, given the ubiquitous nature of shock melts in this meteorite, and indicates that the Rb-Sr isotopic systematics of the mineral fractions have not been significantly reset by shock metamorphism. The fact that olivine lies on the isochron indicates that this phase is probably not xenocrystic in origin and supports the suggestion by [1] and [9] that the disequilibrium between olivine and pyroxene is the result of subsolidus re-equilibrium in a closed system. (p. 1, 2)
So the very same alteration, open system behavior, re-heating, secondary alteration, shock metamorphism, etc. ad infinitum, that is used to disqualify the validity of discordant data somehow miraculously exempts concordant data from befalling the same fate. This state-of-affairs effectively destroys the concept of open system behavior as a reliability criterion, and instead establishes the concept as a convenient rationalization to be used by geochronologists.
Borg et al also recognize the four separate/leachate pairs and plot their slopes in Figure 3. They write:
quote:
Note that the leachates fall to the left and above the mineral isochron and that tie lines (dashed) between mineral separate/leachate pairs have slopes corresponding to ages between 87 and 92 Ma. (p. 2)
The geochronologists attempt an explanation for the separate/leachate pairs:
quote:
However, unlike QUE, the LEW mineral separate/leachate pairs appear to define ages of ~90 Ma (Fig. 3). The chronological relationship between mineral separate/leachate pairs may simply be fortuitous, and reflect ternary mixing between various primary igneous components in the meteorite and secondary alteration products with low Rb/Sr and high 87Sr/86Sr ratios. On the other hand, the fact that the same age is reproduced by four different mineral separate/leachate pairs is not required by ternary mixing, and suggests that Rb and Sr in the host silicates may have been fractionated and partitioned into leachable sites at ~90 Ma. This process may have resulted in Rb loss, but could not have added significant amounts of extraneous Sr. The fractionation of Rb from Sr may be the result of secondary alteration processes or shock metamorphism. (p. 2)
Again, we see how analytical precision of discordant ages requires the concoction of hypothetical geologic processes that allegedly occurred in the distant past. And again, the very reliability criterion — analytical precision — that is used to confirm the validity of concordant data is somehow magically transformed into a fortuitous event when applied to discordant data, for no other reason than the fact that it is discordant. This state-of-affairs effectively destroys the concept of analytical precision (consistency) as a reliability criterion, and instead establishes the concept as yet another convenient rationalization to be used by geochronologists.
Another point of notable interest is that Borg et al reference another study where U-Pb isotopic systematics yielded an isochron of 212+-62 (p. 2). This study increases the range of isochrons to over 58 million years (over 32% of the expected age), with the lowest isochron age at 154 and the highest at 212. If we take the wider range that results from taking the max (212+62) and min (154-6), we end up with a range of 126 million years (over 70% of the expected age). This is a generous gap to be claiming agreement between isochrons.
But have no fear, just as the geochronologist has a pool of excuses to assist him in narrowing the raw data to his liking, he has a pool of pretexts to justify the implementation of a large net for the designation of agreement between isochrons:
quote:
These differences are outside the combined analytical uncertainties calculated from the individual isochrons. It is therefore likely, that despite their textural, mineralogical, geochemical, and chronological similarities, LEW and ALH are derived from different magma sources as suggested by [12] on the basis of slightly different bulk trace element abundances. Differences in initial Sr isotopic ratios of this magnitude are commonly observed in comagmatic terrestrial rocks. Therefore, perhaps the best explanation is that LEW and ALH represent very similar batches of magma that were contemporaneously intruded into the same pluton. LEW may be derived from a slightly different mantle source, or may have had slightly more interaction with the Martian crust than ALH, and thus assimilated slightly more radiogenic Sr. (p. 2)
Amazing. When isochrons are developed that exceed analytical uncertainty — even ranging up to 70% of the alleged age to be confirmed — the geochronologist is free to designate contemporaneous intrusions, or simply claim that some isochrons were produced from a slightly different mantle source, which conveniently allows isochrons exhibiting significant age differences to be considered in agreement while safely bypassing the need for analytical precision.
In any case, I have seen many of these studies in the past few years, and they have greatly succeeded in not only convincing me of the invalid nature of radiometric dating, but of the fact that the long lists of concordant and consistent radiometric ages are simply the knavish product of completely invalid methodologies designed to confirm an outcome that was pre-determined at the outset.
This, that a man’s eye cannot see by the light by which the majority see could be because he is used to darkness; but it could also be because he is used to a still clearer light, and when this is so, it is no laughing matter.
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