JonF
Posts: 634
Joined: Feb. 2005
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| Quote (forastero @ Nov. 19 2011,01:14) | | Quote (JonF @ Nov. 18 2011,06:54) | | Quote (forastero @ Nov. 17 2011,23:34) | | Quote (JonF @ Nov. 17 2011,06:56) | 87Sr is stable. It does not change back int 87Rb or or into any other isotope of Sr.
85Sr is not used in Rb-Sr isochron dating.
Irrelevant. Not terrestrial. |
You said the following was an excellent table http://en.wikipedia.org/wiki.......rontium
Well look at the daughter isotopes of 87Sr
85Sr is used in isochron dating |
Nope. No mention of isochron dating at your reference. Who says 85Sr is used in isochron dating?
| Quote |
Cosmic rays do effect terrestrial isotopes |
Some terrestrial isotopes, yeah. But cosmic rays do not affect any terrestrial isotopes relevant to isochron dating |
Yeah see table 1. 85Sr
<a href="" target="_blank">ftp://ftp.geo.uib.no/pub....f</a> |
Broken link.
Simple. You don't have a clue and you can't read for comprehension.
Here, I'll make it simple for you:
Notice the label above the second column? 87mSr is an excited state which requires significant energy input to achieve. Once it is created, it decays with a half-life of 2.815 hours. It almost always decays back to 87Sr but occasionally decays to 87Rb.
Does this happen in nature? I don't know. But:
- Any excited 87mSr that decays back to 87Sr has no effect on the isochron age.
- Any excited 87mSr that decays back to 87Rb would increase the numerator of the X coordinate and decrease the numerator of the Y coordinate in the isochron diagram, which would decrease the indicated age, which is derived from the slope. IOW, if you want to argue that this excitation happens in nature, you're arguing that Rb-Sr isochrons underestimate the real age.
- Finally, if you are going to argue that this happens in terrestrial nature, you need to provide evidence for it and an explanation for why Rb-Sr isochrons agree with so many other methods. And "They're all lying" isn't an explanation.
| Quote | Here are a few cosmogenic isotopes used in isochron dating 39K, 39Ar, 10Be, 26Al, 3 He, 40K, 33Ar, 36Ar, 37Ar, 38Ar, and 41Ar
Here are just a few quick searches
http://www.ajsonline.org/content....bstract |
Interesting. I didn't know about that one. But in that case it's known that the isotopes are cosmogenic and the method takes advantage of the fact. If you are trying to argue that isochron dating dating is in error, you need to show how cosmogenesis causes error. Huge error.
Gee, another interesting one. But again, they are taking advantage of the cosmogenic nuclide to determine an age. If you are trying to argue that isochron dating dating is in error, you need to show how cosmogenesis causes error. Huge error.
So I have to modify my statement. Cosmic rays do not affect any terrestrial isotopes in a manner that cause errrors in isochron dating.
No mention of cosmogenesis or any cosmogenic nuclides.
No mention of cosmogenesis or cosmogenic nuclides. Yeah, as it says an Ar-Ar isochron can be constructed. It seldom is; an age spectrum diagram is far more common:
| Quote | | The series of ages from an incremental heating experiment are most often plotted as a function of the percent of the 39Ar released. This type of diagram is called an age spectrum or an Ar-release diagram. For an ideal, undisturbed sample, the calculated ages for the successive gas increments are all the same, and the age spectrum is a horizontal line at the value corresponding to the age of the rock (Fig. 3.11a). These same data can also be plotted on an 40Ar/39Ar isochron or correlation diagram (Fig. 3.11b) and will fall on a straight line whose slope is equal to the ratio 39Ar/40Ar in Equation 3.20 and whose intercept is the 39Ar/40Ar ratio of nonradiogenic, or air, Ar. The only difference between the age spectrum and isochron diagrams is that the isochron treatment does not require any assumption about the composition of nonradiogenic Ar; otherwise, the two diagrams are just two methods of visually displaying the same data. |
Dalrymple, G. Brent. "The Age of the Earth". Stanford University Press, 1991, p112.
| Quote | | Oh and please do tell me how 40K is only cosmogenic off earth |
No, you tell me how 40K is cosmogenic on Earth. In space there's a tremendously different intensity and energy distribution of radiation. Buried rocks are shielded to some extent, even more than solar wind/magnetosphere/atmospheric shielding. You made the claim, let's see your support.
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