forastero
Posts: 458
Joined: Oct. 2011
|
| Quote (JonF @ Dec. 08 2011,15:52) | | Quote (forastero @ Dec. 08 2011,16:37) | | Quote (JonF @ Dec. 08 2011,15:27) | | Quote (forastero @ Dec. 08 2011,15:36) | | Quote (JonF @ Dec. 08 2011,08:49) | | Quote (JonF @ Dec. 08 2011,09:24) | | Quote (forastero @ Dec. 08 2011,05:26) | | Quote (JonF @ Dec. 05 2011,16:13) | | Quote (forastero @ Dec. 05 2011,16:28) | | Quote (JonF @ Dec. 04 2011,18:33) | | Quote (forastero @ Dec. 04 2011,13:42) |
Likewise, your isochrons are based on psuedocalibrations that dont exists and probably why JonF refuses to answer my long question about There are countless cases of discordance. |
I haven't seen any such question. You did ask how isochrons work and I pointed out that this is a terrible medium for teaching such things, and gave links (several times) to excellent explanations.
How ya doin' on telling me which of those quotes is your "cited ... proof that contamination is a major problem"? |
Arnt you the same fella that insisted that isochrons are calibrated with Milankovitch cycles? I dismissed it twice but you never respondeds |
No, I'm not that fellow. I don't know how isochrons correlate with Milankovitch cycles, but that correlation has nothing to do with contamination. And isochrons certainly aren't calibrated with Milankovitch cycles.
| Quote | As for contamination here is a good but I will look for some more
Mineral isochrons and isotopic fingerprinting: Pitfalls and promises Geology; January 2005; v. 33; no. 1; p. 29-32; 2005 Geological Society of America http://geology.geoscienceworld.org/cgi........i....29
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. . |
Still not contamination. Note that "Nevertheless, it is possible for initial isotope ratio variation to be obscured in a statistically acceptable isochron." Note also that almost all isochron dating is consilient with other methods such as U-Pb concordia-discordia, by far the most widely used method, and with Ar-Ar, probably the second most widely used method.
If you had any idea of how isochron dating works, you would know that errors due to initial isotope ratio mismatches are rare and why that is so.
You are wasting your time with isochrons. They have their uses, but if you want to discredit radiometric dating you need to be talking U-Pb and Ar-Ar.
I don't have a subscription to Geology, and they don't offer the option of purchasing a single article. Will you send me the PDF of the whole thing? I assume you're not just blindly copying what some creo website has to say ... hee hee hee. |
Of course they calibrate isochrones with Milankovich cycles and vice verse. From your very own Glen Davidson
http://www.schweizerbart.de/resourc....690.pdf |
Goodness me, there is an actual mention of calibration of Ar-Ar from Milankovitch cycles! I suspect that they really meant correlation. But how about the vice-versa? |
And on further investigation I was right, they did really mean correlation. From the full paper at Cyclostratigraphy – concepts, definitions, and applications:
"Despite these caveats, the cyclostratigraphic method has great potential. Major advantages and applications are: ... {long snip} ...
Intercalibration with radiometric dating methods. Comparison and intercalibration with independent radio-isotopic dating methods is fundamentally important. For example, new radiometric age dating recently challenged the up to then widely accepted cyclostratigraphical interpretation of the Middle Triassic Latemar platform in Italy (e. g., Goldhammer et al. 1987, Hinnov & Goldhammer 1991, Brack et al. 1996, Egenhoff et al. 1999, Zühlke 2004). At the Tortonian GSSP at Monte dei Corvi (Italy), however, new 40Ar/39Ar ages essentially confirm the cyclostratigraphic dating (Kuiper et al. 2005). Nevertheless, a detailed comparison of the astronomical and 40Ar/39Ar ages reveals a rather consistent offset of ~ 0.8%, the astronomical ages being older (Kuiper 2003). This study provides an astronomical age for mineral dating standards and opens the possibility for the introduction of an astronomically dated standard in 40Ar/39Ar dating. An accurate and precise intercalibration is especially important by providing tight constraints for the astronomical tuning when it is extended into the Mesozoic."
(bold added). So it's obvious that they cleared up a discrepancy and think that cyclostratigraphy could possible be used to calibrate Ar-Ar dates someday. We're back to no evidence of calibration of one by the other. |
Oh so now intercalibration doesnt mean calibration?
Plus its as clear as day that they are calibrating isochrones with Milankovich cycles and Milankovich cycles with isochrons. Typical circular fervor evocreo |
My my, you're right! Intercalibration does not mean calibration, at least not in that paper! If A is calibrated by B, then if for some reason B changes than A also changes. That's not the case with cyclostratigraphy and Ar-Ar dating. It's clear that in that paper "intercalibration" means agreement between independent results. If the underlying calibration of cyclostratigraphy changed, we wouldn't change the results of Ar-Ar analysis and vice versa. If the results of cyclostratigraphy and Ar-Ar analysis don't agree, that's a problem that needs investigating.
No, it's not "clear as day that they are calibrating isochrons with Milankovich cycles and Milankovich cycles with isochrons." It's clear as day that the are comparing the results of the two different and independent methods and they are glad that they agree closely, but they're a little bothered by a "rather consistent offset of ~ 0.8%". 0.8% when you are looking for 10,000,000%! Hee hee hee ...
In fact, they explicitly say that Ar-Ar is not calibrated by cyclostratigraphy and do not hint anywhere that cyclostratigraphy is calibrated by Ar.Ar. Comparison is not calibration. End of story.
Bottom line: cyclostratigraphy and Ar-Ar analysis agree closely but are not used to calibrate each other.
How 'bout dem references for "contamination is also a problem"? How ya comin' on that search? |
yeah, when they wrote: "new 40Ar/39Ar ages essentially confirm the cyclostratigraphic dating". |
So what? Confirm does not mean calibrate.
con·firm (kn-fûrm)
tr.v. con·firmed, con·firm·ing, con·firms
1. To support or establish the certainty or validity of; verify.
2. To make firmer; strengthen: Working on the campaign confirmed her intention to go into politics.
3. To make valid or binding by a formal or legal act; ratify.
4. To administer the religious rite of confirmation to.
cal·i·brate (kl-brt)
tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates
1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument): calibrate a thermometer.
2. To determine the caliber of (a tube).
3. To make corrections in; adjust: calibrated the polling procedures to ensure objectivity.
See both definitions numbered 1. The agreement between the two independent methods confirms the accuracy of the newer one. No calibration going on here, nothing to see here, move along...
Well, the validity of the methods themselves are "calibrated" by the well-known and well-established laws of physics and chemistry. (Even if the variations you are so fond of posting do actually exist, they do not affect the accuracy of radiometric methods significantly.) There are various tests and physical standards that laboratories interchange to ensure that they are implementing the methods consistently. |
That is also incorrect.
http://books.google.com/books?i....f=false
http://geology.gsapubs.org/content....bstract
All kinds of 14C correction attempts are made to agree with independent calibrations, yet you confidently claim that radioisotopes with huge half-lives are accurately calibrated by their own so called laws of decay. Actually isochrones depend upon all kinds of assumptions. Assumption that are very unlikely when one considers things like quantum tunneling .
The favorite isochron dating method is Uranium-lead (238U /206Pb) where alpha particles tunnel from 238U nuclei through Coulomb barriers of the Thorium nucleus and eventually into 206Pb by a process of eight alpha-decay steps and six beta-decay steps. Quantum tunneling can be suppressed or accelerated by using perturbation pulses and vibrations. A rigorous theoretical analysis based on perturbation theory to first order in the control pulse fields showed that sufficiently frequent perturbation pulses suppress quantum tunneling whereas trains of pulses separated by finite time intervals accelerate tunneling relative to spontaneous decay. Another problem is mechanical oscillation due to vibrations.
http://www.chem.yale.edu/~batist....SB5.pdf
http://online.physics.uiuc.edu/courses....ing.pdf
http://books.google.com/books?i....f=false
http://books.google.com/books?i....f=false
|
