JonF
Posts: 634
Joined: Feb. 2005
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| Quote (forastero @ Nov. 17 2011,01:39) | | Quote (JonF @ Nov. 16 2011,12:09) | | Quote (forastero @ Nov. 16 2011,12:21) | | Quote (JonF @ Nov. 16 2011,10:13) | | Quote | Plus you are still ignoring the following:
Mineral isochrons and isotopic fingerprinting: Pitfalls and promises Geology; January 2005; v. 33; no. 1; p. 29-32
Abstract: "The determination of accurate and precise isochron ages for igneous rocks requires that the initial isotope ratios of the analyzed minerals are identical at the time of eruption or emplacement. Studies of young volcanic rocks at the mineral scale have shown this assumption to be invalid in many instances. Variations in initial isotope ratios can result in erroneous or imprecise ages. Nevertheless, it is possible for initial isotope ratio variation to be obscured in a statistically acceptable isochron. Independent age determinations and critical appraisal of petrography are needed to evaluate isotope data. If initial isotope ratio variability can be demonstrated, however, it can be used to constrain petrogenetic pathways." |
And those independent age determinations almost always result in confirming the isochron age. E.g. Radiometric Ages of Some Early Archean and Related Rocks of the North Atlantic Craton and Radiometeric Dating Does Work!.
| Quote | | Now consider the fact that sedimentary layers, which contain 99% of all fossils, are even more mixed and contaminated than the igneous contamination described above |
You still haven't figured out how sedimentary layers are dated. Repeating myself from page 27:
| Quote | | Well its not usually your so called stable alpha decaying isotopes. Anyway though please do finally teach us why you think the radiometric dating of sedimentary rocks is so accurate. |
Sure. After you read my references and figure out what's going on.
Here's a hint. If sedimentary layer B is above igneous layer A which is 100 million years old and layer B is also below igneous layer C which is 90 million years old, and there's no signs of disturbance after deposition or solidification, how old is layer B?
And if igneous layer D cuts through all layers A and B, obviously by seeping into cracks and then solidifying, but doesn't cut through layer C and dates to 95 million years old, how old is layer B? |
All you are doing is "saying" the sedimentary rocks are uncontaminated and dated accurately, which doesnt make it so. Do you at least agree that sedimentary rocks would have a lot more mixing and isotope contamination than igneous rocks?
What references did you ever give on Sedimentary isochrons? |
Wotta maroon. Can't even read a simple paragraph and extract the meaning. No, I'm not just saying the sedimentary rocks are uncontaminated and dated accurately. I'm not saying that they are uncontaminated, contamination of sedimentary rocks doesn't matter. I'm saying they are dated accurately for the reasons I explained twice.
"Mixing and isotope contamination" in sedimentary rocks is irrelevant although mixing is likely to be less in sedimentary rocks and isotopic contamination is probably about the same as in igneous rocks.
Few if any isochrons are available for sedimentary rocks, because most sedimentary rocks are dated by stratigraphic position relative to igneous rocks, as I already explained twice. Once immediately above.
I dug up one example of directly dating sedimentary rock by an isochron method: Sm-Nd isotopic dating of Proterozoic clay material: An example from the Francevillian sedimentary series, Gabon.
I'm saying the igneous rocks are dated accurately, for reasons explained in detail in the references I've given you so many times. Contamination and initial daughter are accounted for in modern methods. We conclude from theory and experiment that decay rates are sufficiently constant as to not cause any significant errors. |
Those concordant dates were done mostly by the same people and the national center of pseudoscience TAX makes my skin crawl. |
Didn't look at the links, did ya? Those concordant dates were mostly done by different people, and not by a national center of anything.
| Quote | | Again there is no way to know for sure the origin of the daughter isotopes |
Um, yes there is, as detailed in the various references I've given already.
| Quote | | The whole reason that sedimenatary rocks are not usually radiometrically dated is because they are mixed with a vast array of sedimentary stuff. Yes they are dated by index fossils but then the index fossils are in turn dated by the sedimentary rocks? |
No, as I've pointed out several times. They are dated by their relationship to igneous layers.
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