Talk:Radiometric dating

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Archive 1 Archive 2


Radiometric dating a myth?[edit]

Odd wording[edit]

After an organism has been dead for 60,000 years, so little carbon-14 is left in it that accurate dating has not been established. I see someone changed this to say "...that accurate dating cannot be established," which was reverted. Is the intent of the sentence as it stands to say that an "accurate dating method has not been established" for materials of greater age? Otherwise, I'm not sure why "cannot be established" wouldn't be a clearer wording. Agathman (talk) 14:38, 28 April 2009 (UTC)

Reworded some time ago, I guess. Babakathy (talk) 08:40, 9 March 2010 (UTC)

dating rocks younger than a few million years[edit]

I made a table of the isotopes mentioned in this article. Would it be helpful to include it? It would be even nicer if we had authoritative sources for the useful range of dating by each isotope system. But what sticks out when I look at the table is that most of the half-lives are in the billion-year-plus range. Radiocarbon and U-Th are less, but apply to rather special systems and even there cannot be useful beyond perhaps 1 million years. Is there a standard way to date rocks that are only a few million years old, or even younger? --Art Carlson (talk) 09:00, 14 September 2010 (UTC)

Some isotopes used in dating
parent daughter half-life
147Sm 143Nd 106 billion years
87Rb 87Sr 50 billion years
238U 206Pb 4.47 billion years
40K 40Ar 1.3 billion years
235U 207Pb 704 million years
234U 230Th 80,000 years
235U 231Pa 34,300 years
14C 14N 5730 years
3H 3He 12.3 years

Duh! Any isotope with a shorter half-life will have decayed away to nothing since the Earth was formed. Still, what do geologists interested in formations of intermediate age do? And is there anything equivalent to the cosmic distance ladder by which the billion-year methods can ultimately be connected to historical time? (Not that the first principles of radioactive decay are unsound, or that the cross-checks using a variety of methods are not convincing support. I'd just like to know where the limits are.) --Art Carlson (talk) 09:55, 14 September 2010 (UTC)

Conflict with young-earth creationism?[edit]

I would like to suggest adding a section on the conflict between young Earth Creationism and radiometric dating. It would NOT be an argument of the scientific merits of the two positions, as there doesn't seem to be any for the former. However, I do think it would be interesting and valuable to at least acknowledge that radiometric dating is one of the great supports of scientific understanding of the universe, and that it is denied by a faith-based class of people.

Beyond that, I would like to know just how young Earth Creationists attempt to dismiss radiometric dating. I'm sure there are a number of plausible-sounding objections that would take some thinking to refute, just as I'm sure that someone's taken the time to refute each one.

(Apologies if this has already been discussed; the archives seem to have a lot of arguing about whether radiometric dating works, but never talks about what I suggest above.) -- Dan Griscom (talk) 12:36, 1 May 2011 (UTC)

Extreme fringe views are not notable on an article on a scientific subject. If the views of the religious are notable at all they should be discussed in the article about the young earthers. Vsmith (talk) 14:01, 1 May 2011 (UTC)
The scientific refutation of creationist views on the subject is discussed at Creation Science#Radiometric dating. I agree with Vsmith that it does not belong in this article. Dirac66 (talk) 14:33, 1 May 2011 (UTC)

They're a fringe pseudo-scientific belief. They don't need to be mentioned in the articles covering the real science. That gives them undue weight. We have other articles specifically dealing with them. --Harizotoh9 (talk) 13:04, 5 April 2012 (UTC)

Error in the first equation?[edit]

I believe the age equation is wrong. It shows D growing exponentially without bound as t goes to infinity. I believe the correct equation should be:

D = D0 + N0(1-e-λt)

Michael Schmitt (talk) 23:58, 5 June 2011 (UTC)

Actually both are correct. The equation in the article is obtained by replacing N0 = Ne+λt into your equation to obtain:
D = D0 + Ne+λt(1-e-λt) = D0 + N(e+λt-1)
This does not increase to ∞ because N is not a constant. It may seem more mathematically transparent to use the first form in terms of the constant N0, but geochemistry references (such as the one cited by White) tend to use the second form because N is the measured quantity.
However this is the second time I have had to correct this error (see edits 21 Feb 2011) so perhaps the point needs to be made more transparently. I will replace N by N(t) and add an extra explanatory sentence. Dirac66 (talk) 02:46, 6 June 2011 (UTC)

Picture of mass spectrometer[edit]

If I'm not mistaken, the mass spec currently shown, a Thermo DeltaPlus, is used for stable isotopes? Maybe an ICPMS, a TIMS or an argon noble gas mass spec would be more accurate? Cheers — Preceding unsigned comment added by 129.194.8.73 (talk) 14:59, 13 March 2012 (UTC)

No Discussion of Lava?[edit]

A core part of the logic behind radiometric dating is what is happening as the lava is cooling. I don't see any discussion of that in the article. Is the isotope floating about in the air and getting trapped in the lava? Are the parent/daughter concentrations different in the lava from the concentrations in the air? What are the relevant interactions between the lava, the cooled rock and the air? It seems this is yet another scientific Wikipedia article that assumes too much on the part of the reader, that sacrifices satisfying the general public to satisfying the experts. Br77rino (talk) 21:01, 2 April 2012 (UTC)

Lavas (and other igneous rocks) are dated from the minerals that are found inside them and date the cooling of the rock. Lavas are not dated by radiocarbon dating and so don't involve interaction with the air. This article could probably do with a section on the practicalities of dating different types of material - different methods are used for different things. Mikenorton (talk) 23:02, 2 April 2012 (UTC)
First of all, which isotopes are we discussing? Br77rino's question seems more pertinent to K-Ar dating, which does determine the date at which igneous rocks solidified from lava. Before we go any further, could Br77rino please confirm whether s/he was referring to K-Ar, C-14, or some other method? Dirac66 (talk) 00:21, 3 April 2012 (UTC)
I can't help thinking Br77rino might be a little confused - I don't see what air has to do with anything. Perhaps it needs explaining more clearly that both parent and daughter isotopes originate and remain within the rock which is to be dated? Pterre (talk) 08:29, 3 April 2012 (UTC)
For K-Ar dating, the simplest model is indeed that all parent (40K) and daughter (40Ar) isotopes originate in the rock and remain there once the rock has solidified. However this is not always strictly true and there can be a problem of contamination from atmospheric argon. See K-Ar dating#Assumptions for more details. Dirac66 (talk) 13:52, 3 April 2012 (UTC)
OK, but you are assuming that Br77rino is specifically refering to K-Ar, which s/he does not mention. I think a more general 'layman's terms' explanation could be added. Pterre (talk) 17:47, 5 April 2012 (UTC)

Assumptions[edit]

It would be helpful to qualify some of the assumptions required for different types of radiometric dating. While a few of the sections make mention, what about adding an 'Assumptions' heading? Major assumptions must be made, with the first being that we know the approximate levels of isotopes when the rock was created, and the second being that the levels of breakdown or radioactive decay have been consistent over time. As an ancillary assumption, we must also presume that no isotopes were lost or gained between the formation of the rock or material and the time of measurement. It presumes a constant level of energy and a relatively consistent environment to make these predictions. A variety of events may change the results, where something like even a major flood, changes in geologic and/or volcanic conditions, or a large solar flare on the sun might impact the calculation, let alone a super nova explosion, meteor, or other unknown cosmic event. For example, the frequency of supernova throughout the universe is estimated to be much higher than recently shown in our Milky Way, whereas such an event within about 100 Ma may impact isotopic values. — Preceding unsigned comment added by Sunny monday (talkcontribs) 01:06, 25 December 2013 (UTC)

Please read the section on preconditions which deals with the matter or parent/daughter isotope ratios and nuclide loss, and the age equation section on that matter and on initial compositions.Babakathy (talk) 08:23, 2 January 2014 (UTC)

Isochron diagram[edit]

The isochron figure has several errors and is long overdue for correction, so I'm just letting everyone know that I and my graduate students are going to fix this in the near future.Radiogenic (talk) 17:17, 23 September 2014 (UTC)