faded_Glory

Both LordValentine and myself have explained this several times to you already. But never mind, here we go again:

Both the parent material and the original daughter material (say, Rubidium and Strontium) will most likely vary in concentration from place to place in the original magma, and therefore in the resulting crystalline rock. That’s fine, and nothing to worry about in the isochrone method (all it means is that on a Sr87/Sr86 vs Rb87/Sr86 crossplot the points will be spread out along the Rb87/Sr86 axis). If we didn’t use the 3-isotope method, however, we would have reason to be worried about variable concentrations of original daughter material Sr87 because that would yield different dates for different samples from the same rock (unless there wasn’t any Sr87 originally present at all).

But, the ratio of Sr87/Sr86 tends to be the same throughout the magma and the initial rock. Again, this is because the isotopes are chemically identical (same number of protons and electrons). Apart from a relatively small change in atomic mass (caused by the different number of neutrons, therefore the subscripts 86 and 87) there is nothing to tell them apart. There is no reason why there would be differentiation in the magma between Sr87 and Sr86. Also, the reactions that take place during cooling will have no preference for either one of the isotopes (I have to qualify that there are examples of mixed magmas where there can be differences in isotope ratios because of different provenance).

In any case, if there was differentiation, it will show up in the radiometric analysis because the points as measured in the present would not line up. The isochrone method is therefore self-diagnostic for ‘bad’ magmas: the points don’t line up, so the assumptions are invalid and no conclusions are drawn regarding the age of the rock. Such cases exist, and are published – as are many examples where the points do line up, which is unlikely in the extreme if they hadn’t started off aligned because of constant Sr87/Sr86 in the first place.

BTW, did you read Wiens? Did you check out my Ar-Ar example (similar to Rb-Sr)?

fG

Douglas J. Bender

LordValentine,
Because I thought it had to do with algebra/mathematics. I admit I was a bit hasty, and that I didn't fully understand the reasoning involved (but as I've said, a great deal of that was due to ardipithecus' failure to adequately describe his reasoning).

I don't think that. As far as I knew, ardipithecus was offering his own, original reasoning, and it was primarily a "mathematical" line of reasoning, which seemed to hinge on some simple chemical and geological properties which did not seem beyond a layman's grasp (and perhaps actually isn't, really).

Applied Mathematics (though I took all the mathematics courses offered, except for maybe two or three). I graduated 10 years ago, and haven't really even looked at a college-level textbook, or used mathematics, since (other than various snippets of things I read over the Internet, and some books I might intermittently check out at the library).

Yes, it seemed somewhat odd to me that someone could make such an obvious blunder as I thought ardipithecus had made. Turns out I was the one who had made a blunder. But I am not arrogant in my opinion of my ability to understand and reason, LV.

Wise advice, which I will try to heed. I should have known better myself, but I guess I got somewhat caught up in the "spirit" of this place (you know, "My Gawd, what an idiot!", etcetera).

You don't know how difficult it was. Kind of like walking into a KKK meeting, and shouting, "Jesse Jackson rules!"


In Christ,

Douglas

Douglas J. Bender

fg,


Actually, I don't know if I read Wiens. But I think I understand why the isochron method would be "self-diagnostic". However, I can see I would need quite a bit more knowledge of chemistry and geology to adequately judge the method (its assumptions, basically).

In Christ,

Douglas

S2Focus

Hmmmmmm.......

Douglas J. Bender

S2Focus,


Yes, as long as the "science" does not require a high degree of training in a particular field in order to evaluate the validity of its reasoning. In the case of "isochron dating", in order to evaluate the validity of some of the assumptions, one would need a fair degree of knowledge regarding chemistry and geology. I was referring to general reasoning ability regarding scientific issues which could be evaluated by a layperson, such as whether similarity of "design" necessarily implies a common ancestor (it does not), etcetera. And once the unstated (or at best obliquely referred to) explanation regarding the reasoning behind testing various parts of the rock was described, I admitted that I had made an error - so, it's not really fair to blame someone for failing to understand all the implications and unstated assumptions of someone else's explanation, actually.


In Christ,

Douglas

Ragnarok

Make plans now people! We need to be setting aside leave time to go to the stoning (Deut 13:10) when this fails to happen and Bender is revealed as a false prophet.



And none of this "awww we can go to a stoning any day" nonsense. This is a stoning NONE of you can afford to miss.

sh0k0nes

Douglas,

Just in case u missed it:

"Douglas, does this now convince you of the validity of Rb/Sr dating? If not, why not?

fG"

Kev

Boro Nut

I'm right with you on that one. On my last Everest expedition we got as far as base 2 and found there was only 1 oxy bottle between the pair of us.

Boro Nut

Consequently I had to turn back, and missed out on fulfilling a lifetime's dream and achieving everlasting fame. Still, never mind eh! At least I didn't die at base 5 like him.

Douglas J. Bender

I thought I'd at least sort of answered that in one of my more recent posts in this thread - I'd said that I'd need to know more about chemistry and geology before I could make a sound judgment about some of the assumptions underlying that kind of dating. The reasoning is valid, but the assumptions upon which it rests might not be.


In Christ,

Douglas

Douglas J. Bender

What part of "I believe there is very strong reason to believe" (that something will happen soon) constitutes a PROPHECY, Rag? I suggest you set aside the stones you've been gathering in your zeal to be the one to kill a prophet.


In Christ,

Douglas

[ May 18, 2002: Message edited by: Douglas J. Bender ]</p>