JonF
Posts: 634
Joined: Feb. 2005
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| Quote (forastero @ Nov. 19 2011,19:43) | | Quote (JonF @ Nov. 19 2011,17:24) | | Quote (forastero @ Nov. 19 2011,17:24) | | Quote (JonF @ Nov. 19 2011,08:42) | | 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. |
Here is the 85 Sr in table 1 again <a href="" target="_blank">ftp://ftp.geo.uib.no/pub....f</a> |
Still broken. This board mungs URLs all the time. Try making it small at http://tinyurl.com/....url....url.com
| Quote | Hey now dont go shifting goal posts again
I was merely showing you how cosmogenic isotopes like 39K, 36 Ar, 39Ar, etc... etc... are used in isochron dating. |
Well, it certainly seemed to me that you were implying that cosmogenic isotopes cause errors in isochron dating. If you weren't, well, then it appears you don't have a point or any suggestion of a mechanism for errors in dating.
| Quote | | Oh and as far as 87mSr and 87Sr, thanks but thats about what I was saying |
IOW you were babbling about radioactive 87Sr for no reason whatsoever.
Do you have any evidence that 87mSr or 40K are formed in terrestrial conditions?
Do you understand the effect if 87mSr is formed in terrestrial conditions?
So do you have a point about radiometric dating? Do you accept the results? Or do you reject the results for any rational reason?
Have you figured out how sedimentary layers are dated?
Do you still think Rb-Sr isochron dating is the most widely used method? |
Are you actually saying that it wouldnt effect isochron dating if true |
I assume you're referring to 87mSr? Why, yes, I am saying it wouldn't affect isochron dating significantly if it were created in nature. I already pointed out above how Rb-Sr isochron dating would be affected if 87mSr were created in nature (it's the opposite of what you want it to be), and I have no reason to believe that 87mSr is created in nature. The use of cosmogenic isotopes as cosmogenic isotopes in isochron dating means that such dating would not be affected by cosmogenic isotopes.
{ABE} Of course, I do have some reason to believe that 40K and 87mSr are not created on Earth in any significant quantities; the consistency between K-Ar/Ar-Ar dates, Rb-Sr dates, and the various dates that cannot be affected by cosmogenic isotopes: U-Pb concordia-discordia, SM-Nd, ...{/abe}
What you seem to want to do is argue that errors are introduced in isochron dating by the fact that some cosmogenic isotopes might possibly be created on Earth and those cosmogenic isotopes are not accounted for. Or that errors are introduced in isochron dating by the fact that some methods of isochron dating explicitly take advantage of the existence of cosmogenic isotopes. If it's the latter, WTF? If it's the former, your first step (which you haven't taken yet) is to demonstrate that relevant cosmogenic isotopes exist on Earth.
(There's a lot of steps you haven't even thought of after that, but let's start simple).
| Quote | | I am telling you that things aint as stable as you think and are probably getting more unstable as are so many of the world's cycles. Besides, your and Tracy's insistence that cosmic rays have different powers in different places only strengthens that argument. |
Ah, the ol' vague "maybe someday somewhere something will be discovered that overturns everything, therefore we know nothing". What you attempt to tell us is only relevant when you include evidence. Nobody cares what your unsupported opinion is.
Physicists know a lot about nuclei and why they decay or don't decay. Things are exactly as stable as we think.
| Quote | | I didnt realize that the dating sedimentary rocks via igneous rocks were so extensive and these debates have left me even more suspicious of it . |
With, of course, no rational reason for that.
| Quote | | Sb-Sr is definitely the most popular for sedimentary rocks but I do agree with you now that its not the most popular for other rocks |
Well, you haven't supported your claim the Rb-Sr is the most popular for sedimentary rocks, but it hardly matters because such a small percentage of all dating is done on sedimentary rocks.
| Quote | | As for the link below, there is a full PDF on google |
Then post the link or post the search terms that bring it up. You can try posting the link in code tags: click the "Code" button in the compose window.
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