I have a question if the world is supposed to be 4.6 billion years old then why or how would Rubidium-strontium dating where rubidium-87 to strontium-87 has a half-life of 50 billion years. And have we ever had one of these specimens reach a full half-life?
Rubidium-strontium dating
No but what is the point?
Scientists have caldulated it pretty accurate, they could be slightly of, however slightly on 50 billion yea....
he wait the...
half life of Sr 87 is: 2.7 hours (EDIT this is wrong)
but yes of Rb it is 47 billion years, but scientists have an accurate way of calculating it. If they are of it is not by much.
Last edited by Klaw 2 on Sun Jun 29, 2008 6:24 pm; edited 1 time in total
Scientists have caldulated it pretty accurate, they could be slightly of, however slightly on 50 billion yea....
he wait the...
half life of Sr 87 is: 2.7 hours (EDIT this is wrong)
but yes of Rb it is 47 billion years, but scientists have an accurate way of calculating it. If they are of it is not by much.
Last edited by Klaw 2 on Sun Jun 29, 2008 6:24 pm; edited 1 time in total
If you take the trouble to read the article ON THIS MATTER which YOU ASKED FOR in the religion/philosophy forum you will find the answer. The article I referenced gives a complete explanation of isochronic radiodating techniques, including Rubidium-Strontium dating.
No matter how much you try, you won't make radiometric dating say that the world is 6000 years old. Live with it.
No matter how much you try, you won't make radiometric dating say that the world is 6000 years old. Live with it.
| DavidkChase wrote: |
| I have a question if the world is supposed to be 4.6 billion years old then why or how would Rubidium-strontium dating where rubidium-87 to strontium-87 has a half-life of 50 billion years. And have we ever had one of these specimens reach a full half-life? |
i think your question is incomplete, because it makes no sense logically or grammatically.
But if you are asking how we can determine the 4.6 Gya age of the Earth using the Rb-Sr radiometric dating when the half life of ⁸⁷Rb is 48.8 Gya, the answer is that you have to understand how radioactive decay and dating works.
i can try to give you a short answer, though.
At its core, all that's going on in radiometric dating is counting particles, and of course the number of particles changes by virtue of radioactive decay. So, in our case, we're counting the number of ⁸⁷Rb particles. At any given time, the number of ⁸⁷Rb particles in a sample is:
| Code: |
| N = N₀ × 2^(-t/h) |
| Code: |
| N = N₀ × 2^(-1)
N = ½N₀ |
So, to determine the date all you do is count the number of ⁸⁷Rb particles, and use the first equation. All you need is the half-life of ⁸⁷Rb (which we know) and the number of ⁸⁷Rb originally in the sample (which you get using the isochron technique - it's a clever trick, but really complicated to explain), and you can solve for t. Voilà, radiometric dating - simple.
Now, the reason why we use ⁸⁷Rb with its 4.88 Gya half-life has to do with the counting. We could theoretically use ¹⁴C with its 5730 half-life or ⁸²Se with its half-life of 0.13 Zya - hell, we could use any isotope, theoretically - but it is very hard to count very small numbers of particles. Look what happens when we use t = 4.6 Gya (and N₀ = 100%) for each case:
| Code: |
| C : N = 0.000...% (too small to display)
Rb : N = 93.7% Se : N = 99.999999998% |
If we had an isotope with a half-life of around 4.6 Gya, that would be cool, but the tricky part then would be determining the starting count. We can do that with rubidium-strontium dating using the isochron technique, but we can't do it with just any isotope. Since we can use the isochron technique for rubidium-strontium dating, and the half-life is in the right range to give us a decent count, it is a useful dating tool. (Incidentally, if we use the 1.248 Gya half-life of ⁴⁰K which is used in potassium-argon dating, we get 7.8% - which, again, is a solid number, easy to count.)
| Klaw 2 wrote: |
| half life of Sr 87 is: 2.7 hours |
You might want to double check that figure. ^_^;
| Indi wrote: | ||
You might want to double check that figure. ^_^; |
I did...
He lol there is a misprint in my textbook they mixed something up
(before it crosses your mind, I'm noy being lame and trying to deny I was wrong).
Sorry for the wrong info,
Maye I misread or misunderstood something but.
my book says:
number_symbol_massnumber __ Weight____% in nature__ half life_____decay-particle thingy (know the dutch word not the english)38_____Sr_____87___________86,90889___7.02%_____2,7 Hours___y
flaw in book or am i doing something wrong?
Last edited by Klaw 2 on Sun Jun 29, 2008 7:01 pm; edited 2 times in total
Strange - either the textbook is wrong or the translation is wrong.
Strontium 87 is stable (it doesn't decay at all and therefore has no half-life).
Are you sure you are not looking at another isotope?
PS - looking at my periodic table...perhaps you might mean Krypton 88 (halflife 2.77 hours) ? or Kryton 87 (halflife 78 mins) ?
Strontium 87 is stable (it doesn't decay at all and therefore has no half-life).
Are you sure you are not looking at another isotope?
PS - looking at my periodic table...perhaps you might mean Krypton 88 (halflife 2.77 hours) ? or Kryton 87 (halflife 78 mins) ?
Oh, i see what happened - the clue is the "decay particle thingy", it's γ (gamma) radiation. That's not a regular isotope, that's a metastable isotope usually formed during a nuclear reaction. Those are normally very, very short-lived, then they decay back down to the regular isotope, usually emitting γ rays. ~3 hours is actually pretty long for a metastable isotope, although there are a few that are much longer.
In other words, what you're looking at is not regular ⁸⁷Sr, it is ⁸⁷(m)Sr.
In other words, what you're looking at is not regular ⁸⁷Sr, it is ⁸⁷(m)Sr.
| Indi wrote: |
| Oh, i see what happened - the clue is the "decay particle thingy", it's γ (gamma) radiation. That's not a regular isotope, that's a metastable isotope usually formed during a nuclear reaction. Those are normally very, very short-lived, then they decay back down to the regular isotope, usually emitting γ rays. ~3 hours is actually pretty long for a metastable isotope, although there are a few that are much longer.
In other words, what you're looking at is not regular ⁸⁷Sr, it is ⁸⁷(m)Sr. |
?
afraid not, i think it is just a flaw, but look for yourself:
whole page: (though scaled down...)
http://www.putfile.com/pic/8360993
the important bit:
http://www.putfile.com/pic/8361005
(click on full size on the bottem under the pic)
its in dutch but the translations:
Atomic number_symbol_massnumber __ Atomic mass____% in nature__ half life_____decay-particle (radiation type) and amount of energy.
| Klaw 2 wrote: | ||
? afraid not, i think it is just a flaw, but look for yourself: whole page: (though scaled down...) http://www.putfile.com/pic/8360993 the important bit: http://www.putfile.com/pic/8361005 (click on full size on the bottem under the pic) its in dutch but the translations: Atomic number_symbol_massnumber __ Atomic mass____% in nature__ half life_____decay-particle (radiation type) and amount of energy. |
Oh my, you're right - your book is misprinted. It gives all the data right for ⁸⁷Sr, but then adds the half-life and radiation type for ⁸⁷(m)Sr! And it can't be data for ⁸⁷(m)Sr because the mass and natural abundance would be wrong.
Here's how you know there's something fishy: if ⁸⁷Sr had a half-life of 3 hours... how could it 7% abundant in nature? (Unless it was being created all the time, at such a high rate that the amount of strontium in nature is doubling every 3 hours... which is a little hard to believe for an element as heavy as strontium.) Either the half-life is way too short, or the % in nature is way too high.
another of the great misteries of life solved!
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