Talk:Radiocarbon dating

PLEASE ADD NEW TOPICS TO THE BOTTOM

Constant cosmic ray flux assumption

Since it is assumed that the cosmic ray flux is constant over long periods of time, carbon-14 is assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to nonradioactive carbon throughout the Earth's atmosphere and oceans is constant.

I'm pretty sure the above is false since:

Beryllium 10 is useful for studying the geology from hundreds of thousands of years ago mainly because it has a half-life of about one and a half million years. In addition, there are two key factors that have affected beryllium 10 production over the last 200,000 years: the earth's magnetic field and the sun's magnetic activity. When there are high-intensity solar magnetic storms, more charged particles are interacting with cosmic rays, and less beryllium 10 is produced. Likewise, the earth's magnetic field changes the flux of cosmic rays into and out of the atmosphere. EurekAlert

-In response to the above: The solar storms only cause a cosmic ray influx in the short term, in the long term it's either negligable or included as part of the average rate of production.

-In response to the above: The current rate of C14 decay is not as large as the current rate of C14 production (differences of 15-30% are quoted).

-Because of calibration curves, this assumption doesn't have to be true for C14 to accurately measure the age of an object (I've added this statement to the article). Samboy 20:50, 11 Apr 2005 (UTC)

-The assumption that the relative isotopic abundance of C-14 is constant was successfull for the development of the method, but is only approximately true (this is the reason why one needs calibration curves). Variations of cosmic radiation and of reservoir exchange rates have influenced the atmospheric radiocarbon abundance. Deviations of about 10% during the last 10,000 years are visible in the calibration curve, 26,000 years ago the relative radiocarbon abundance was even 60% higher (column "Delta 14C" in http://www.rlaha.ox.ac.uk/O/intcal04.14c). --Peter.steier 18:41, 14 September 2005 (UTC)

Calibration curves as basis for dating

Is it your position that the calibration curves are the basis for radiocarbon dating accuracy? If so, then what is your position on the bristlecone pine measurements that I posted in the dendrochronology talk page? Wdanwatts 02:27, 12 Apr 2005 (UTC)

My position is that the assumption that C14 levels have been fairly constant is a reasonable starting base for dating items. However, this assumption is not necessary because of the existance of calibration curves. Basically, we get almost the same namers from calibration curves that we get from just assuming that C14 levels have been constant for the last 10,000 years. We have two independent ways of getting at the same data. The chances of both methods giving us mostly the same data by pure chance is really small. Samboy 02:36, 12 Apr 2005 (UTC)

Is not the fact that the calibration curves make "small" corrections sufficient to ensure consistency between the results with or without "calibration"? How does that bolster the results? Dan Watts 13:51, 16 Apr 2005 (UTC)

About the graph on Bristlecone data posted to the dendrochronology discussion, note that zero widths can't be measured. They mean missing rings as inferred from comparison of patterns in several cores. Thus, the graph is not relevant to the discussion. Jclerman 20:35, 3 October 2005 (UTC)

Standard deviation

Is is really the standard deviation that is indicated by +/- ? That should indice the e.g. 95% confidence limit. The difference is (at least) a factor of two!)

It is as is common with all publishing of measurement results. And it is not the error of the dating but only that of the ¹⁴C content of the purified carbon actually being measured. I have just written a paragraph about that in the German version of the article. - Axel Berger 14:57, 6 January 2006 (UTC)

Kudos

Great article! --Yak 16:50, Feb 22, 2004 (UTC)

Calibration Curves

Please educate me as how speleothems (which appear to mainly use U/Th means for dating) can be used to calibrate C14 dating. It looks like using a yardstick to calibrate a micrometer. Wdanwatts 18:35, 13 Apr 2005 (UTC)

Speleothems, at least some of them, have layering due to variations in seasonal precipitation, etc. The calcium carbonate of the speleothem uses CO2 from the air & water. The older end of the C-14 scale can be matched with the shorter end of the U-Th scale, presumably. The question I have here is the ancient carbon in the waters that was dissolved out of the limestone by the water on the way to the speleothem. Vsmith 20:35, 13 Apr 2005 (UTC)

As long as I am asking, how about some explanation of how the sources listed in the article --ice and deep ocean cores, lake sediment varves, and coral--, (all but dendrochronology) contribute to the C14 calibration. To me, the links look to have tenuous (at best) connections to C14 calibration. Wdanwatts 19:43, 13 Apr 2005 (UTC)

Ice cores have annual layers which are countable. The cores also contain inclusions of trapped air which contains CO2 and therfore C-14. Deep ocean seds and lake varves are layered sediments w/ presumably annual layering, these contain carbon within the seds that has C-14. Coral is built by organism in crude? layers and carbon is present from the corals. Correlate the layering - check with C-14 dates.

Hope this simple explanation helps, although there is a lot more in the details and I may have mixed things up a bit :-). Vsmith 20:35, 13 Apr 2005 (UTC)

Perhaps you could put that in the Ice cores article. It tells of needing 2000 to 6000 annual layers of snow to becom impermeable to air. I don't see how having an averaging factor that large can allow much calibration of the C-14 dates. Wdanwatts 12:51, 14 Apr 2005 (UTC)

Hmm.. just read that, and it does state that correlation problems exist. Looks like the ice core article is currently undergoing some revision by Tonderai with some references. More to explore there, cheers. Vsmith 13:57, 14 Apr 2005 (UTC)

There is a lot to explore there. When searching in the ice field of research, remember to also search for "firn" and "snow pit". (SEWilco 06:01, 16 May 2005 (UTC))

Question

Does this article address the fundamental fallacies of Radiocarbon dating? 1. Assuming that the rate of formation and decay of C14 have reached equilibrium? 2. Assuming that after two or three half lives the amount of C14 is still measurable?

This is nonsense. After one half-life, half the amount is left. After another half-life, half the amount of half the amount is left, that is 1/4 of the original amount. Whether this is measurable depends on what the original amount was. Why don't you just read the article? I guess you are a creationist? --Hob Gadling 11:15, August 1, 2005 (UTC)

Controversy

Carbon dating is often criticized in creationist circles as unreliable. I believe this is due to some cases in which the method yielded results that were later effectively disputed (possibly because the carbon dating made a constant cosmic ray flux assumption), but I don't know enough about this to be sure.

I think it would be a valuable addition to this article if some mention of these arguments were made, preferably with counterarguments. Anyone more knowledgable than I am willing to take this up? Great Cthulhu 16:29, 1 September 2005 (UTC)

The cases were not disputed because of cosmic rays, they were disputed because the creationists who cited them did not understand carbon dating. For example, they thought that dating the shells of living molluscs is relevant for evaluating the method. [1] --Hob Gadling 13:38, 29 September 2005 (UTC)

Further, I posit that if any of that ilk really wish to put up or shut up on their ideas, they can make a "What's wrong with anything that says the Earth is older than I say it is" entry, and failing that, they'll start shitting up this entry on their own accord. Part of the spooky-action-at-a-distance of NPOV is dialectical, isn't it? Opposing points of view will somehow find a stable equilibria or whatnot? Let's not violate that principle by trying to present the point of view of someone who wishes to destroy all understanding of radiocarbon dating with a false controversy. They'll be in here soon enough as it is. --Mayor Of France 18:49, 3 October 2005 (UTC)

Mayor Of France, I have yet to make up my mind on this (potential?) controversy. However, what is wrong for having people provide (valid) counter-arguments? Would it not be better for all parties involved to fight fair with sturdy facts, instead of engaging in "piranha attacks" as you have started to do? What benefit is there to raising the decibel level on this discussion? Surely, one would hope that the end result is that Wikipedia would come up with an article that can stand the test of time from rational people.

FWIW, no one has yet to posit the trollish "What's wrong with anything that says the Earth is older than I say it is?" argument. Surely, there are enough reasonable people here that will keep at bay those seeking to "...destroy all understanding of radiocarbon dating with a false controversy..." Are you saying that it is a false controversy simply because you have deemed it as such?? Perhaps you are of the opinion that Creationism/Intelligent Design advocates are predisposed to being disagreeable? If that is the case, it seems it has yet to present itself here. Please refrain from assuming the worst and give this debate a chance to be fair.

To date the only source of criticism of this technique has come from the young earth/creationism types. To elevate their unscientific attacks to the level of 'controversy' is to give them more status than they are due. As in most areas of science where their ideas cannot find traction, this group is now stooping to trying to inject the false impression that there is some internal debate in the field, thus providing a foothold for doubt. Doubt that they hope to exploit to foster their own interpretation of events. DV8 2XL 17:50, 10 December 2005 (UTC)

"what is wrong for having people provide (valid) counter-arguments?" Nothing. The problem is: there are no known valid counter-arguments, but a humongous heap of invalid ones. Every time a creationist (or ID person) presents a counter-argument (against evolution, natural selection, common descent, an old earth, or dating methods), it turns out to be based on ignorance or duplicity (hard to tell which). That's my experience. --Hob Gadling 19:36, 11 January 2006 (UTC)

Introduction

Is there some reference for the recent change to the extreme limit of radoicarbon dating from 50,000 to 60,000 years? Dan Watts 19:01, 22 September 2005 (UTC)

Yes, from a Google search:

COSMIC BACKGROUND REDUCTION IN THE RADIOCARBON MEASUREMENT BY SCINTILLATION SPECTROMETRY AT THE UNDERGROUND LABORATORY OF GRAN SASSO, by Plastino, W. et al. Radiocarbon, Volume 43, Number 2, 2001, pp. 157-161(5).

Excerpt: The cosmic noise reduction observed at the laboratory of Gran Sasso makes it possible to perform high precision 14C measurements and to extend for these idealized samples the present maximum dating limit from 58,000 BP to 62,000 BP (5 mL, 3 days counting). [2]

Impact on Archaeology

Is there any reference to substantiate this diatribe? Dan Watts 03:14, 25 September 2005 (UTC)

Removed here pending addition of references and cleanup:

== Impact on archaeology ==

Radiocarbon dating had a large impact on archaeology, particularly on many of archaeology's theoretical assumptions until this tool was introduced after World War II. In effect, radiocarbon dating established that many artifacts are now known to be far older than previously thought, and thus going back to earlier ages than otherwise could have been if they had been only the inspired and diffused products of the Near Eastern civilization. Therefore, the notion that the ancient Near East was the fount of global human civilization can no longer hold true. Clearly, various centers of civilization arose independently of one another even if the Near Eastern one remains the oldest on record.

Vsmith 15:35, 29 September 2005 (UTC)

Basics

An anon person said "There is also another way of finding the absolute date of something using radioactive dating. First, find the fraction of un decayed material and find out how many times you have to multiply it by itself to get the fraction (n). In Example: 1/8 of the parent material is left. you would need to do 1/2 * 1/2 * 1/2 to get 1/8. Therefore, the n would equal 3. Secondly, you multiply n * (one half life in years)= Age in years"

1. If this is another way, which one is the "other"?

2. The materials don'd decay. The radiocarbon atoms in the material decay.

Jclerman 03:19, 23 November 2005 (UTC)

Yes, I was going to remove that - you beat me to it :-) Seems to be quite simplistic and contains a couple of confusing errors. Doesn't really belong here and I assume the subject is better covered in radiometric dating, at least I hope it is :-) Vsmith 03:40, 23 November 2005 (UTC)

Nitrogen: Molecules or Atoms?

In the equation with a neutron bombarding a N-14 atom to produce a C-14 atom plus hydrogen, one would assume that it is indeed the atom and not the molecule involved in this reaction.

However, there is a statement about 80% of the atmosphere being nitrogen, but doesn't that refer to the molecular form and not the atom? What is the actual percentage of monatomic nitrogen in the atmosphere? Kenny56 07:39, 20 December 2005 (UTC)

The amount of monatomic nitrogen in the atmosphere is likely to be rather small. However, since the neutron energy necessary to bombard N-14 into C-14 is large, the electronic configuration would have a vanishingly small effect on collision cross-sections. Dan Watts 13:18, 20 December 2005 (UTC)

Whoa now Dan, where did you come up with large neutron energies being necessary for N-14 into C-14? Do you know this to be true in fact? You seem to have spoken in excess of your knowledge on this subject, which severely damages your credibility. Look up the isotope 14 of carbon and how it is created, then look up the energy of thermal neutrons. Kenny56 07:25, 27 December 2005 (UTC)

Well, I guess that knowing that the free neutrons came from cosmic ray interactions is not sufficient to determine their energy. Mea culpa. Dan Watts 02:43, 9 January 2006 (UTC)

Don't be too shy about that. Unless someone can pinpoint a source of thermal neutrons in thin upper atmosphere, I'd say there aren't any. Thermalizing neutrons in the short time they have before decay or absorption is not an easy thing to do. - Axel Berger 07:42, 9 January 2006 (UTC)

Nitrogen appears to have the highest covalent bond strength of all the diatomic molecules, so it has a high affinity to bond or stay bonded with itself, which explains why the concentration of monatomic N is so low. The article needs to reflect the correct nitrogen species and concentration in the atmosphere.

The next questions that comes to mind are how the C-14 bonds to oxygen to form the CO2, does it gather two oxygen atoms or glob onto an O2 molecule? And, would the free Hydrogen atoms created with C-14 seek to form H2 molecules and/or compete with the C-14 for the available oxygen atoms/molecules in forming water molecules? Kenny56 07:30, 27 December 2005 (UTC)

This thread appears not to be related to the techniques of radiocarbon dating. Experts on this topic are probably available in one of the cosmochemistry or nuclear chemistry discussions. Jclerman 18:33, 28 December 2005 (UTC)

What's up with the bold print? I would expect that the experts in the techniques of radiocarbon dating would also be experts in the simple chemistry upon which the techniques rely, or at least have the knowledge to explain the basics, would they not? If you can contribute to the discussion then please do so, but feel free not to chime in if you can't.Kenny56 08:23, 7 January 2006 (UTC)

I just happened to wonder about this same question and found a recent thread discussing it here. I'm not sure I understand the answer. Are you saying that the nuclear reaction takes place on an N atom in an N2 molecule, which then splits up into one N and one C? These parts then subsequantly recombine in the environment into new N2 and CO2? Adding this to the article would make the picture more complete. Woodstone 22:33, 29 December 2005 (UTC)

A neutron does not interact at all or only negligibly with the electrons. From the point of view of the neutron there is no difference between a bound or free atom or one in an ionized state. All that matters is the cross section (physics) of the nucleus for the reaction of interest. Axel-berger 17:29, 5 January 2006 (UTC)

Thanks for the above observation. Sounds clear. So then we get a molecule of CN. Is that chemically stable? Or does fall apart in N and C atoms right away? −Woodstone 21:26, 5 January 2006 (UTC)

No probably not. I do not know what energy the proton in the conversion is emitted at, but typically nuclear binding energies are so much higher than chemical ones that the recoil ought to break the molecule apart. You're left with two ions or radicals and the rest is simple atmospheric chemistry.Axel-berger 14:10, 6 January 2006 (UTC)

According to data found on other wiki pages, the free neutron absorbed by the nucleus of the nitrogen atom to produce the C-14 atom is known as a thermal neutron and has an energy of 0.025 eV. The diatomic nitrogen molecule has a triple covalent bond with a bond energy of 946 kJ/mol, or 9.79 eV. BTW, a CN molecule is also known as cyanide, which is toxic to mammals. i'm still searching for answers to the simple atmospheric chemistry questions, but not finding much to fill in the gaps.Kenny56 08:23, 7 January 2006 (UTC)

When I said "simple atmospheric chemistry" I did not mean it was simple as such, but extraneous everyday stuff that need not concern us here. Do not forget we're talking about a concentration of 10^-12 (one part per billion or in America even only one part per trillion) of atmospheric carbon, or 0.4x10^-15 of atmospheric gases. Chemically any of its compounds are totally irrelevant and in equilibrium they'll all end up as CO2 anyway. - Axel Berger 23:44, 7 January 2006 (UTC)

Actually I do not know a lot about that reaction - the ones I've been taught are those relevant to power plants. But I'm pretty certain there are few thermal neutrons up there, you need a lot of dense stuff like water or carbon with a very low absortion coefficient for them to bounce off often enough to thermalize (lose very high initial kinetic energy down to thermal equilibrium) without vanishing. But even if your numbers are right, they're irrelevant here. The interesting bit is not the purely kinetic energy of the incident neutron before the reaction but the energies set free by the nuclear reactions themselves. What you need to look up, if you have sources to hand, is the typical energy of the emitted proton.

The one thing I have found is that 15N itself is stable, so it must be an excited state generated by the binding energy set free on absorbing the additional neutron into 14N that leads to the decay.

14N + n --> 15N --> 14C + p (= 14C + H)

I seem to have lost my nuclid table, but if you find the data, add the masses of 14N and a free neutron and subtract that of 15N, you get the energy released in the capture. - Axel Berger

Formulae

I wonder if the formulae at the end cannot be expressed simpler (without detour through natural log) as follows:

$N=N_{0}\times 2^{-{\frac {t}{t_{1/2}}}}$, resulting in $t={t_{1/2}}\times {}^{2}\!\log {\frac {N}{N_{0}}}$

−Woodstone 22:33, 29 December 2005 (UTC)

1. Something is amiss in this new expression proposed for t, if I test it by plugging in a simple N/No ratio of 1/2, I don't obtain the expected 5568 yrs BP.
2. What is gained by using logs base 2 rather than logs base e?

Jclerman 00:08, 30 December 2005 (UTC)

Sorry, I forgot t_½ (now added above). The advantage is no need for the extra parameter λ: only t_½ is used. −Woodstone 10:23, 30 December 2005 (UTC)

Insider information

1. Why get rid of lambda? The inverse of the constante lambda is a useful and well known value for a physicist. It's the mean or average life of a radioisotope. For radiocarbon its value is close to 8000 yrs [lambda is close to 1.2x10(exp -3)]. These easy values allowed us, in the "prehistoric" times of the development of the radiocarbon dating technique, to mentally evaluate approximated results (dates and their uncertainties) while a dating was in progress during the several days required. For example, from lambda's value it can be derived that 1% decrease in radiocarbon activity corresponds to about 80 yrs.
2. Why not log base 2? Because lambda's usefulness. Moreover slide rules didn't have base 2 log scales. During Libby's lifetime we used long slide rules with LL scales to compute radiocarbon dates. In fact the first electronic portable digital calculator which I saw was the one Libby showed us, as a novelty, from the podium in a Radiocarbon Dating International Conference, in New Zealand, in 1972.

by Jclerman 16:59, 30 December 2005 (UTC)

These are mostly historical arguments: we do it that way because we've always done it that way. How long since you last used a slide rule? I have seen "half life" much more fequently than "average life", so it would make sense to eliminate λ. However, if experts do it overwhelmingly with natural log, I will not insist further. Thanks anyway. −Woodstone 17:52, 30 December 2005 (UTC)

The thing I do not understand is why historically the half-life was chosen in the first place. At the time exponential decay was an old hat and a commnplace formaula to all physicists - see current in a coil or charging a capacitor. All these processes are governed by their time constant Tau, i.e. the inverse of Lambda. Why the first researchers into radioactivity did not choose this but something entirely new, unusual, and impractical is a mystery to me. Could it be because they tended to be chemists and not physicists and not used to mathematical calculations?Axel-berger 14:14, 6 January 2006 (UTC)

Earth's Magnetic Field Decay

The earth's magnetic field was measured by Gauss in 1835 and has been repeatedly measured since then showing an exponential decay with a half-life of ~1400 years. So it is likely that the earth's magnetic field strength was 8x higher just 4200 years ago. Would not this stronger field provide greater cosmic ray protection to the earth and possibly reduce the C-14 production rate from its current rate? Do the calibration curves take the magnetic decay effect into account? Kenny56 08:10, 20 December 2005 (UTC)

Calibrations are performed by comparing the known dates of a series of samples, with the corresponding radiocarbon dates. This bypasses the origin and the value of all factors that affect the atmospheric radiocarbon level. Jclerman 18:30, 28 December 2005 (UTC)

Essentially, the calibration curves take some other (assumed) temporal marker(s) {tree-ring dating, varves, speleothems, ice cores, etc.} and compare how the dating results from those methods align with C-14 dating technique result. So, specifically these calibration techniques ignore the earth's magnetic field strength since it is (usually) not necessary for such measurements as dendochronology (and except for theoretical computations, it doesn't enter into the C-14 dating calculation). However, if the C-14 production rate were affected, that SHOULD show up in the C-14 calibration (with the exception of dendrochronology, I don't know what source(s) of C-14 would be used for the cross-correlation). Dan Watts 20:27, 20 December 2005 (UTC)

The magnetic field does tend to change a lot over time, but it is totally wrong to extrapolate a recent trend far into the past. Incidentally the field broke down to something like a tenth of the current value around 38 ka ago. You can find that in the calibration as highly elavated ¹⁴C values at the time. This is just about the time of the demise of the Neanderthals in Europe. I am currently trying to find out by how much ground level radiation might have risen then and if that might have been enough to disrupt the biosphere. Probably not, but I do not know yet. - Axel Berger 15:05, 6 January 2006 (UTC)

Please explain the time units for "38 ka ago", what is ka? And what is the reference or source of this statement that the field broke down to 1/10 of the current value? Thanks, Kenny56 03:58, 7 January 2006 (UTC)

Let me guess ka is short for kilo-annus, a thousand years. −82.171.189.187 05:29, 7 January 2006 (UTC)

Yes, "ka" is the common notation for kiloyear. As to sources I can only cite recent lectures given by our in-house specialist Dr. Bernhard Weninger and recently by Prof. Dr. Pieter Meiert Grootes from Kiel. As to radiation killing off Neanderthals my former teacher of radiation protection, Prof. Hans Bonka of RWTH Aachen, has just told me I was spouting nonsense, same as I used to do back then. Apparently the atmosphere itself shields us so good that changes in the field do not matter down at ground level - flying spacecraft and international air routes is another thing. (And of course he backed that up with data and numbers I ought to have known - all from his lectures at http://www.lrst.rwth-aachen.de/vorlesungen/index.php.) - Axel Berger 00:07, 8 January 2006 (UTC)

Cyoub said: Obvious mathematical error. Show your work.

ATTN: Cyoub

• Thanks for your one liner comment. I've now tried to clarify the nomenclature and expand on the physics and meanings that determine the directions of the time arrows. You could have gained insight into the existing deficiencies by plugging in the halflife value, a simple N/No ratio of 1/2, and see that you obtained a result of -5568 which means a date 5568 BP years. Please, check the current version and let me know of further deficiencies observed. Jclerman 18:44, 25 December 2005 (UTC)

Total rework

I have just seen that there is at least one other contributor to the sister article in German here too. That article has been voted one of the "good articles" there. While it would be a lot of work incorporating that material here, a straight translation and replacement might be doable. Doing that we might also clean up the duplications that have crept into the German one. While in no way offering to do it all, I would do my share. Comments? - Axel Berger 00:17, 8 January 2006 (UTC)

The role of Hessel de Vries

C-14 dating was first presented by the Dutch professor Hessel de Vries, who applied it for archeological purposes. De Vries also did substantial work on the counting tubes and later showed that some of the assumptions by Libby were wrong, eg, De Vries showed that the C-14 content wasn't constant over time, the so-called "De Vries effect". Libby received the Nobel prize for his work in 1960, but many seem to feel that had De Vries not died in 1959, the two would have shared the Nobel prize. I think this article could reflect this, or at the very least credit De Vries for his contributions. [3]

Corrections and amplifications:

Until somebody writes a paragraph about Hessel de Vries's contributions, the whole story is told by Willis in one of the references which I've included in the article. Willis calls de Vries "the unsung hero of radiocarbon dating."

H. de Vries :

• Proposed, tested, and used a better method than Libby's for radiocarbon dating, using CO2 gas in proportional counters.
• His chemical preparation lines, electronics, etc. were cloned in all European laboratories in the late 1950s.
• He studied the variations of atmospheric radiocarbon in the Northern Hemisphere and hypothesized that they correlated with solar activity and climate change (probably the first oblique reference to the now known as global warming). He cited work by a Dutch meteorologist, Barendsen (?) which probably was related to the later known El Niño and La Niña "oscillations" in ocean temperature.
• His was probably the first C14 geochemical model including the biosphere and hydrosphere.
• He also did extensive archaeological (and geological?) dating including the study of the Piltdown hoax.

Feel free to elaborate on some or all of the above and include it in the article.

Jclerman 19:40, 20 January 2006 (UTC)