Radiometric Dating and the Geologic Column: A Critique

Wow.Several days of preparation, five posts, and no evidence or data. Just more unsupported assertions.

Yes.One possibility is a "mixing isochron", where your samples are composed of mixtures of sources with different isotopic compositions. The slope of the line thus produced has no age significance. This is illustrated and discussed at Mixing of two sources. I would have stressed diagnosis somewhat differently. A straight line on a mixing plot is a necessary but not sufficient condition for a binary-mixing "isochron"; straight lines may appear on a mixing plot even when the isochron has age significance, because (due to the physics of mineral solidification) the 87Sr/86Sr ratio commonly is inversely correlated with the Sr content. However, it is IMHO immensely significant that mixing "isochrons" have random slopes and should therefore have negative or ridiculously large positive slopes around half the time .... but such slopes are very rare, indicating that mixing isochrons are rare. (And the fact of finding a mixing isochron is often publishable; e.g http://www.the-conference.com/JConfAbs/5/116.pdf). Of course, many isochrons do not plot as straight lines on a mixing plot, proving that they are not binary mixtures. (It's theoretically possible to generate a false isochron, that does not plot as a straight line on a mixing plot, with three or more components in the mixture, with one component being a very unlikely composition such as zero parent and zero daughter, but let's not bother with such obviously rare scenarios). Finally, mixing often leaves physical indicators in the rock.Another, moderately common, scenario is a metamorphic event in which the minerals in the rock are isotopically homogenized relative to each other but the overall rock reamains closed. Then the "whole rock" isochron still reflects solidification, but the isochron based on sampling the individual minerals separately indicatess the age since metamorphosis. See Dating Using Sr Isotopes, and the PDF about the Martian meteorite to which Anti-Climacus linked appears to exhibit a similar structure. Yup. The principle is similar to the metamorphic scenario I mentioned above. It's done more by isotope geochemists than geochronologists. Aint specialization grand?

Your "analysis" of the Borg et al study, consisting as it did of no more than protestations of how little you believed it and unwarranted pejorative phrases, demonstrated nothing more than your abilities ... and painted a sad picture of those abilities.Try looking at the evidence, and analyzing it with statistics and mathematics rather than belittling it based only on your prejudices.

He's referring to Rb-Sr ISOTOPIC SYSTEMATICS OF THE LHERZOLITIC SHERGOTTITE LEW88516, to which he referred in message 60 on page 4 of this thread. That's the message that starts out "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.". Since then, of course, he's totally ignored our specific objections raised before and after that message, and just beat the Borg et al drum over and over again.The text to which he refers is:"Our age agrees well with the U-Pb analysis of LEW leachates and residues completed by [5] which intersect concordia at the lower intercept at ~170 Ma, as well as with the Rb-Sr age of 187 12 determined on ALH by [6]. Although the U-Pb isotopic systematics of Y79 are complex, [11] have argued that their best data intersect concordia at 212 62 Ma, and are therefore also in good agreement with the LEW Rb-Sr isochron. ...[5] Chen, J. H. & Wasserburg, G. J. (1993) LPSC XXIV, 275-276
[6] Shih, C. -Y. et al. (1982) GCA 46, 2323-2344
[11] Misawa, K. et al. (1997) Antarctic Meteorites XXII
NIPR, 115-117"So, he's demonstrated that he doesn't know the difference between concordia-discordia dating and isochron dating. Of course, he also doesn't have any idea about the significance of the upper intercept of a discordia line and the concordia curve, and he doesn't have any idea what they mean by the lower intercept, and why that value may or may not be significant, and why they feel it's significaant in this case. He probably doesn't even know what they mean by metamorphism, and what effects it might have on radioisotope analyses.All in all, he doesn't understand anything that's presented in that paper. All he knows is that he doesn't like the results.

You still have not responded to any of our points. Message 100, if you please.

One of these days ...I actually sat down last week and did the code to generate an animated GIF of a rock aging on a concordia-discordai diagram, in the same vein as my animeted isochron.

I was doing a little digging, and found that the Borg et al paper we have been discussing is actually a preliminary result; there's much more data and discussion in Constraints on the petrogenesis of Martian meteorites from the Rb-Sr and Sm-Nd isotopic systematics of the lherzolitic shergottites ALH77005 and LEW88516, and there's a nice (and very long ... 60 pages) review article at AGES AND GEOLOGIC HISTORIES OF MARTIAN METEORITES.I can't resist adding a little more response: You have demonstrated nothing. You've made a lot of claims, but you have provided no support for those claims other than your personal inability to conceive the results being correct. To demonstrate anything, you need to discuss the mainstream explanation and maybe some other alternate explanations, the evidence and reasoning that leads you to believe your interpretation is correct, and point out exactly how the mainstream explanation is not consistent with accepted principles or knowledge of science. You haven't even made an attempt.