Wikipedia:Peer review/Radiocarbon dating/archive1

Radiocarbon dating

This peer review discussion has been closed.
I've listed this article for peer review because I would like to get it to featured article level. I've done a fair amount of work on it, and have created two sub-articles, in addition: radiocarbon dating samples, and calculation of radiocarbon dates. These are linked, per summary style, from the appropriate sections of the article. I'd like feedback on anything that would be required for FA -- this means not the subarticles, but if there's anything in those articles that should be brought up to this article, I'd like to know. Conversely, if there are other sections where the article could be shortened by making another subarticle, I'd like to know that too.

Thanks for any feedback. Mike Christie (talk - contribs - library) 01:55, 2 July 2014 (UTC)

Comments from Aa77zz

I've looked at this article in past and I'm impressed with the recent improvements.

Physical and chemical background

• You show the decay of carbon-14 in a figure but do not explain what the symbols represent. Consider including the breakdown inline as in the Carbon-14 article:

$\mathrm {~_{6}^{14}C} \rightarrow \mathrm {~_{7}^{14}N} +e^{-}+{\bar {\nu }}_{e}$

with an explanation of the symbols. Perhaps mention that beta particles are electrons.

I've added the equation, and an explanation; the symbols don't perfectly match the svg image, which predates my involvement with the article. Is the image useful now? I see a couple of problems that would need to be fixed if I were to keep it: the symbols are slightly different, e.g. for the electron and anti-neutrino; and the explanation of decay includes a reference to the ratio, 10¹², and the fact that the decay reduces that ratio. This is not addressed in the text at this point. I have an svg editor and can change the image if necessary, or it could just be cut. Mike Christie (talk - contribs - library) 10:34, 3 July 2014 (UTC)

I think the picture can be removed as it doesn't add anything to the article - and could confuse. Why does the first equation have N⁺ rather than simply N? Aa77zz (talk) 10:56, 3 July 2014 (UTC)

I've removed the picture. The plus was added in this edit; the edit summary was "balance the charge", and I see that it does that, but I'm not convinced it is any clearer this way. I left it on the assumption that this conforms to a standard in these kinds of equations, but perhaps that was wrong. Should I cut it again? Mike Christie (talk - contribs - library) 01:18, 4 July 2014 (UTC)

I still don't understand why the nitrogen has a plus in the C14 creation reaction. The symbols represent nuclei (not atoms). There are 7 protons and 8 neutrons on either side - ie in terms of charge +7 on each side. Perhaps there is some subtlety that I'm not aware of. Have you an authoritative source? Aa77zz (talk) 14:27, 5 July 2014 (UTC)

I found a source and removed the +; the source does not include it. I assume the reason the other editor added it is that ¹⁴N would have 7 electrons, and ¹⁴C would have six, so the electrons would not balance; they must have considered it as an atomic equation, rather than as a nuclear equation. Mike Christie (talk - contribs - library) 19:57, 5 July 2014 (UTC)

• "The ratio of ¹⁴
  C to ¹²
  C in the carbon exchange reservoir is 1.5 parts of ¹⁴
  C to 10¹² parts of ¹²
  C." -> The ratio of ¹⁴
  C to ¹²
  C in the carbon exchange reservoir is approximately 1.5 parts of ¹⁴
  C to 10¹² parts of ¹²
  C.

  Done. Mike Christie (talk - contribs - library) 10:35, 3 July 2014 (UTC)

Principles of the method

• "The ratio of ¹⁴
  C atoms in the original sample, N₀," The article introduces the ratio here while N₀ has been defined to be the actual number. I can't see an easy solution without adding complication.

  Good point; this was confused. I've had a go at fixing this; let me know if that's an improvement. Mike Christie (talk - contribs - library) 10:43, 3 July 2014 (UTC)

Invention

• The text uses carbon-14 rather that ¹⁴
  C. Is this deliberate?

  No, it's just carelessness. Fixed. Mike Christie (talk - contribs - library) 10:46, 3 July 2014 (UTC)

Errors and reliability

• Counting statistics. The example is for counting beta particles. If, as I suspect, dating nowadays uses AMS exclusively, then perhaps it is not such a good example.

  I can't tell if beta counting is still in wide use. I suspect it is, because it's a lot cheaper to build a beta counting lab than an AMS lab. The most recent source I have that unequivocally talks about the continuing use of beta counting is Walker's Quaternary Dating Methods, which was published in 2005. I have noticed that Groningen and Belfast, two of the best known labs, have converted to AMS, which certainly implies that AMS has finally overtaken beta counting as the best way to get a precise radiocarbon age. I haven't been able to find a source that definitely states beta counting is on the way out. Mike Christie (talk - contribs - library) 10:57, 3 July 2014 (UTC)

Contamination

• I don't think you need the equation here. It follows directly from the text and doesn't lead anywhere.

  OK, cut. Mike Christie (talk - contribs - library) 10:58, 3 July 2014 (UTC)

Measurement

• Beta counting: If dating by counting beta particles is no longer used then perhaps this section could be shortened.

  See comments above. I am planning to ask an archaeologist I know to do a "subject-matter expert" review, and perhaps he'll be able to settle it, or will know someone who knows the answer. Mike Christie (talk - contribs - library) 10:59, 3 July 2014 (UTC)

  Also, in looking for something else I noticed that beta counting is still discussed as a current method in Malainey's A Consumer's Guide to Arcaheological Science, which was published in 2011. Mike Christie (talk - contribs - library) 11:09, 3 July 2014 (UTC)

• Accelerator mass spectrometry: Are the details of a mass-spec device really necessary? Also you could point out that AMS but not beta counting can determine ¹²
  C:¹³
  C (and hence fractionation).

  I think the picture is helpful, mainly in showing the streams of ¹²
  C, ¹³
  C, and ¹⁴
  C separated as the output of the device. I think readers who aren't clear on the text will immediately understand what AMS does when they see that picture, even if they don't quite understand how it does it. I cover the details of AMS internals partly because the need to add the accelerator component was a big deal; it added a huge amount of cost, and was the main reason why AMS did not spread more quickly once it was clear it worked well. Do you feel these details are a digression?

  Re fractionation: I found one source saying that some AMS facilities can also measure fractionation in the sample, so I'll add something to that effect. I'm a bit surprised that the source says only some facilities can do this; I can't see why all facilities wouldn't be able to. Mike Christie (talk - contribs - library) 11:20, 3 July 2014 (UTC)

Calibration

• I'm not convinced that you need to mention that uncorrelated errors are added in quadrature. This is more "How to" - which wiki is not. I don't think the "The output of CALIB" fig adds very much.

  The secondary sources spend a fair amount of time on the question of how to combine errors. I think a reader not familiar with statistical errors is going to naturally make the mistake in red in the "calibration error" graph; it would seem sensible to take the outside bound of both sigmas and treat that as the one sigma error on the result. So I think something should be said. I know when I first looked at the INTCAL graphs and saw the error bars, my reaction was "why don't they show those errors in the textbooks?" and the answer is because the error is added to the radiocarbon age reading before using the intercepts. I wouldn't mind simplifying the explanation -- perhaps if I take out the equation, and just use the text description?

  Maybe the CALIB figure doesn't add what I wanted it to. What I wanted readers to see from it was that it produces a probability distribution, not just a range. I picked that particular date range so readers could compare the output to the intercept method on the other graph. The intercept method gives the illusion, which several sources comment on, that the date is definitely within the range; the probability method makes it much clearer that sometimes the date is going to be well outside the given range. Do you feel this information is adequately conveyed by the text? Mike Christie (talk - contribs - library) 11:46, 3 July 2014 (UTC)

Notes/Footnotes/References

• Using the both titles "Notes" and "Footnotes" is confusing. I suggest Notes/References/Sources

  I would like to keep "References" to refer to the list of works, since that seems to be the standard -- WP:FNNR says any heading can be used but says "References" is the most common here. I agree "Notes" and "Footnotes" isn't ideal, but I think there would be a similar confusion between "References" and "Sources". How about "Endnotes" for the text notes, and just "Notes" for the footnotes that simply give the source? Mike Christie (talk - contribs - library) 12:12, 3 July 2014 (UTC)

• There are many little problems with consistency.
• Do first names come before or after the last name?
• Do initials have punctuation?
• When there are two initials, is there a space between them?
• Some References (Sources) use templates, others not. The are many tiny differences: "and" or "&" introduced, period after isbn etc. I suggest all use templates (editor1-last= etc)

That is all for now. I hope some of the above is useful. Aa77zz (talk) 13:46, 2 July 2014 (UTC)

Very helpful; thank you very much. I've responded to most of your points above; I will work on the consistency issues and post here again when I think I've cleaned them up. Mike Christie (talk - contribs - library) 12:12, 3 July 2014 (UTC)

I've now done quite a bit of citation cleanup. Please let me know if you still see inconsistencies. Thanks again. Mike Christie (talk - contribs - library) 16:56, 3 July 2014 (UTC)

A few additional comments

• There should be cite for the decay equation in the section "Physical and chemical background".

  Done. Mike Christie (talk - contribs - library) 13:07, 5 July 2014 (UTC)

• Do you really need both equations in the Fractionation section? Perhaps keep just the second?

  Agreed; I've cut it. Mike Christie (talk - contribs - library) 13:07, 5 July 2014 (UTC)

• Is there some way that the time scale for carbon dating could be made more prominent in the lead? Currently, fifty thousand years is mentioned, but only in terms of the calibration.

  Done; this wasn't really covered in detail in the body either, so I added a note in the "Errors and reliability" section. Mike Christie (talk - contribs - library) 13:07, 5 July 2014 (UTC)

• For my own curiosity I tried to check whether beta counting is still used by scanning the latest issue of Radiocarbon (vol 56, issue 2). Of the 21 articles that I looked at, 16 mentioned AMS. It was unclear which technique was used for the remaining 5 - but counting wasn't mentioned.

  I wouldn't be surprised if you're right, but I can't find a source that says this. The most recent source that mentions beta counting as current practice is Malainey (2011). I suspect I can get the answer by asking an archaeologist I know, but I don't know how to cite it. I suppose if it does turn out that beta counting is now rare, I could at least reverse the order of explanation in some sections -- though I also like keeping the historical sequence. Mike Christie (talk - contribs - library) 13:14, 5 July 2014 (UTC)

• I came across an article that might be useful for the "Reporting dates" section:

Millard, Andrew R. (2014). "Conventions for Reporting Radiocarbon Determinations". Radiocarbon. 56 (2): 555–559. doi:10.2458/56.17455.

Thanks; I added some material based on that. Mike Christie (talk - contribs - library) 14:17, 5 July 2014 (UTC)

• I've made small changes to formatting of the references - aiming for consistency. I find the referencing system used in the article very odd. I'm used to a system in which the short cites including the year rather than the title. The treatment of chapters in edited books is also not what I expect. For #32 the short cite in the Footnotes would be "Schoeninger (2010), p. 446." while the full details in the References would be:

Schoeninger, Margaret J. (2010). "Diet reconstruction and ecology using stable isotope ratios". In Larsen, Clark Spencer (ed.). A Companion to Biological Anthropology. Oxford: Blackwell. pp. 445–464. ISBN 978-1-4051-8900-2.

Notice that chapter titles and journal article titles are normally in sentence case, while book titles and journal titles are in title case.

I agree. I'm going to make this change throughout and come back to your other points when this is done. I think the style I used was simply inherited from when I first began editing Wikipedia, and had paid very little attention to the referencing system. Mike Christie (talk - contribs - library) 10:31, 5 July 2014 (UTC)

Aa77zz, how should journals be handled? Would you suggest they be listed in the references, and a short form used, or should I leave them as they are, cited directly from the footnotes and not listed in the references? Mike Christie (talk - contribs - library) 10:46, 5 July 2014 (UTC)

I don't have a strong view on this. FAs use both systems - Jimfbeak for example doesn't use the short form for journal article. When journal article are 10s of pages (unlike Science and Nature) then it helps the reader if one cites the actual page. In these cases it makes sense to use the short form- especially if one has several cites to different pages in the same journal article. The short form is not used for web sources.

In writing the above I noticed that you cite Bowman for the Libby's Nobel prize. I usually try to avoid web sources but in this case I would cite: "The Nobel Prize in Chemistry 1960". Nobelprize.org. Retrieved 5 July 2014. This is unlikely to suffer from link-rot. Aa77zz (talk) 13:05, 5 July 2014 (UTC)

I think I've dealt with everything that was cited from a book; I'll hold off on the journals until you comment on how those should be done. Mike Christie (talk - contribs - library) 12:14, 5 July 2014 (UTC)

For edited books I think you've haven't realised that the template automatically does everything for you - and avoids having the year twice. I'll tweak them now. Aa77zz (talk) 13:05, 5 July 2014 (UTC)

Ah. I was going to ask about that duplicated year; thank you for those fixes (and the other tweaks I see you're doing). Mike Christie (talk - contribs - library) 14:17, 5 July 2014 (UTC)

• Congratulations on tackling this important topic. The article is clearly written and well referenced. Aa77zz (talk) 07:52, 5 July 2014 (UTC)

  Thanks; I am glad you think so. I'm sure there are more improvements to be made, of course. Mike Christie (talk - contribs - library) 10:31, 5 July 2014 (UTC)

Edited books

• In the References section I've now added the page numbers of the chapters in edited books. Previously only Post (2001) had the pages specified. I used google (I'm not near a library). I came across a couple of errors in the authors.
• "Tunis, C.; Zoppi, U. (2004)" actual has 3 authors and a different spelling of the first author. I've changed it to "Tuniz, C.; Zoppi, U.; Barbetti, M. (2004)." Google preview available here.
• "Šilar, Jan (2004)" actually has 3 authors, and Šilar is the middle author. It is now "Košler, Jan; Šilar, Jan; Jelìnek, Emil (2004)." Google preview available here.
• This level of carelessness is worrying (I'm assuming I haven't made errors myself). I haven't checked whether the cited page actually supports the text.
• On an unrelated issue, in the Calculations section is a sentence: "A common standard sample is HOxII, 1,000 lb of which was prepared by NIST in 1977 from French beet harvests.[55]" The cite is to a chapter published in 1984 available here. This is 30 years ago and the technology has changed enormously since. I suspect that this info is really only of historical interest. Aa77zz (talk) 08:29, 6 July 2014 (UTC)

I understand your comment about carelessness; I knew I wasn't the best at dotting every i, but when I saw the number of corrections you had to make, even before reading your comment above I was planning to apologize to you. I should have done a pass through to find these simple errors before bringing the article to PR. I am sorry you've had to spend your time on this sort of tedious work; next time I bring something to PR I'll do my best to make sure it's clear of these mistakes.

On the Tunis & Zoppi article, I have no explanation for what I did. As it happens, Google Books has two different versions of the book: ISBN 1-58603-424-3 comes up if you search for "Physics Methods in Archaeometry, Volume 154" in books.google.com. This is the one you cited, with authors Tuniz, Zoppi, and Barbetti. There is also one with ISBN 1-58603-385-9, which comes up if you search for "Physics Methods in Archaeometry edited by M. Martini, M. Piacentini". That one shows only Barbetti as the author of the article in the table of contents. However, Tuniz and Zoppi show up in the running head, so it seems to be just an error in that edition; and in any case, since I omitted Barbetti, it can't explain what I did.

For Šilar, the reason I put only one name down as author is that in the table of contents the subsections of that paper are attributed specifically to individual authors, and I assumed I should only give his name in that case. The overall section of the book does have the three authors, but perhaps the title I used should have been the more specific subsection, "Radiocarbon", with page range 150-179?

As for the HOxII, I believe it is still in use as a standard -- it was prepared a long time ago, but testing standard samples is a part of every lab's procedures, and the HOxII standard seems to be still the usual choice. I think I saw a more recent reference that stated this explicitly; if I can find that I will add the reference.

Thanks again for all your work on this. I'm really sorry about the work you've had to do to deal with my mistakes; and I really appreciate the help you've given me. Mike Christie (talk - contribs - library) 11:50, 6 July 2014 (UTC)

I've now added the additional HOxII reference; it appears it is still in use, as of 2007, at least. Mike Christie (talk - contribs - library) 12:46, 6 July 2014 (UTC)

I'm pleased that I could make a small but hopefully useful contribution to the article. Aa77zz (talk) 12:52, 6 July 2014 (UTC)

I've changed the Šilar reference to just the one author, with the title and page range constrained to just the part of the chapter that Šilar wrote alone. Mike Christie (talk - contribs - library) 23:30, 6 July 2014 (UTC)

Comments from Jim

• by eating the plants or by eating other animals. — avoid repeated verb

  I took out the second half of this phrase; I think it's obvious to the reader. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• photosynthesis, polyvinyl acetate —link

  Done. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• Nobel Prize in chemistry —chemistry is capped in linked article

  Done. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• than 7 years.—spell out numbers less than 10

  Done. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• Because the solubility of CO2 in water increases with lower temperatures —You would expect "heavy" CO2 to be more soluble than the standard form, is there any detectable effect of differential solubility?

  I agree this is plausible but I can't find anything about it in the sources, so perhaps the effect is not significant. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• Do you need multiple links to dendrochronology and Hans Suess?

  Repeated links removed. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

• Very comprehensive, good work. My FAs tend to have less technical stuff to aid readability, and to me there is too much on, for example, calibration. However, the fact that you are more diligent than me is scarcely a reason for complaint Jimfbleak - talk to me?

  Should some of that material be moved to a subarticle? My feeling is that calibration is so important that I needed to cover it in quite a bit of detail -- a radiocarbon age simply doesn't tell you enough on its own, and calibration can give quite surprising results. On the other hand, it's still quite a long article, even with the two subarticles I've already created.

  Thanks for the review. Mike Christie (talk - contribs - library) 10:05, 9 July 2014 (UTC)

I'll leave the length to your judgement. Articles like this are more likely to be reviewed by people with a scientific background, so it's probably OK Jimfbleak - talk to me? 06:13, 10 July 2014 (UTC)

A few comments

Hello, Mike -- Just one comment for now. I may add others later. Will work my way slowly through the article. In the second paragraph of the lead, you have:

"The most important of these was the need to determine what the proportion of 14 C in the atmosphere had been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is used to convert a given measurement of radiocarbon in a sample into an estimate of the actual calendar age of that sample."

There's just a bit of disconnect between these two sentences. I know the sentence before this referred to "much work" that needed to be done (by scientists), and I believe the phrase "the resulting data" was intended to refer to the data resulting from work done to answer the question regarding the proportion of 14 C in the atmosphere, but there's a stretch between "the resulting data" and the "work" mentioned two sentences earlier. You never actually say that that proportion was determined. You also switch from past tense "was the need" to present tense "is used", with no assist to the reader. There is no hint of a connection between the time of Libby's work in the 1940s and actually using the technique today. I'd like to suggest the following wording:

"Research done to answer this question yielded data which, displayed in the form of a calibration curve, is now used to convert the amount of radiocarbon in a sample into an estimate of the sample's actual calendar age".

I would add "now" before "used" so that it reads "is now used", and, just to simplify the last sentence, instead of "used to convert a given measurement of radiocarbon", I would say simply "used to convert the amount of radiocarbon". I hope you don't consider this nitpicking. I just think it would add clarity and improve cohesion of the paragraph. CorinneSD (talk) 20:43, 10 July 2014 (UTC)

I've revised those sentences to "The development of the technique required much additional work; including research to determine what the proportion of ¹⁴
C in the atmosphere had been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's actual calendar age." I think this reorganization solves some of the problems you identified. I would prefer to keep "a given measurement of radiocarbon", rather than "amount of radiocarbon", because it's not directly the amount that's measured -- what's measured is the ratio between the radiocarbon and the other carbon in the sample. I also took out "displayed", because it's not really the visible form of the curve that's relevant; it's the underlying data. Mike Christie (talk - contribs - library) 00:59, 11 July 2014 (UTC)

2) In the first paragraph in the section Radiocarbon dating#Atmospheric variation is the following sentence:

"Carbon-dating the wood from the tree-rings themselves provided the check needed on the atmospheric 14C/12 C ratio: with a sample of known date, and a measurement of the value of N (the number of atoms of 14 C remaining in the sample), the carbon-dating equation allows the calculation of N0 (the number of atoms of 14 C in the original sample), and hence the original ratio."

It's not clear to me what is meant by "original sample" or "original ratio". I understood everything else in this section, but not this. Perhaps there is a more precise way to refer to the sample and the ratio. Also, in the phrase, "with a sample of known date", are you referring only to a sample of tree-rings or to a sample of any material? CorinneSD (talk) 21:12, 10 July 2014 (UTC)

This is confusing, and I'd be glad of help in improving the phrasing here. The equation in question is the first one in the "Principles of the Method" section:

$N=N_{0}e^{-\lambda t}\,$

The number of ¹⁴
C atoms in any sample containing carbon is N₀; after time t, some of the ¹⁴
C decays, and there are N atoms left, instead of N₀. If a sample is taken from a given tree ring that we know was formed in, say, 1862, we can measure the amount of ¹⁴
C to be found in that sample now. We can then use the equation to determine N₀, which is the amount of ¹⁴
C that would have been in that particular tree ring in 1862. Since we have a set of tree rings from consecutive years, this lets us measure how much ¹⁴
C was in the atmosphere in each of those years -- by measuring N, and calculating N₀, for each year. So by "atoms of ¹⁴
C in the original sample" I meant "atoms of ¹⁴
C that would have been in that sample if it had been taken from the tree ring at the time that tree ring formed."

If you can make this clearer and easier to understand, that would be great. Mike Christie (talk - contribs - library) 00:59, 11 July 2014 (UTC)

@Mike Christie: I took what you gave me, above, and re-worded the sentence. I think it's clearer now. What do you think? I keep looking at the next sentence, the one starting "Armed with...". I think it is a bit long and wordy. I also see your statement, above, that the calculation of N₀ was done for each year. I'm wondering whether we can incorporate that. Something like this:

"After calculating N₀ for each year using the tree rings, scientists used the results to construct a calibration curve that allows them to correct errors caused by the variation over time in the 14C/12C ratio."

I don't think this is quite right yet. One problem with this wording is that the values of N₀ apply to the specific tree-ring sample, not to the year -- that is, N₀ is a count of atoms in a given tree ring, not a piece of data about a given year. Hence I don't think we can say "after calculating N₀ for each year". I'd also prefer to keep the passive voice, for consistency with the rest of the article, rather than say "scientists". I also think it's better to make "calibration curves" plural; I'll expand on that below. Mike Christie (talk - contribs - library) 11:03, 13 July 2014 (UTC)

By the way, is this calibration curve the same as, or different from, the calibration curve mentioned in the lead? Are there two different calibration curves involved in radiocarbon dating, or just this one? CorinneSD (talk) 15:24, 11 July 2014 (UTC)

I'm not really referring to any specific curve here -- that's why I phrased it as "possible to construct". If you have a set of data that tells you, for example, that in 1055 AD the ratio of ¹⁴
C in the atmosphere was 1.2 parts per million, and which includes similar information for other years in the 11th century, then if you measure the ¹⁴
C/¹²
C ratio in a sample of old wood you find, and discover that according to the radioactive decay equations it would have had only 0.6 parts per million of ¹⁴
C in 1055, you can be sure that that sample of old wood is a lot older than 1055. A lot of measurements have been done on tree rings and other things such as varves, and researchers have put together many different calibration curves using that data. There's a "consensus curve", called INTCAL, that has been around since the 1990s; it represents the collaborative efforts of many researchers in the field. Even that curve comes in multiple varieties, though; one for the northern hemisphere, one for the southern hemisphere, and one for marine samples. It's also been through many iterations: INTCAL13 is the current version, but the 2004 version (INTCAL04) had significant differences. Then there are the curves people assembled before INTCAL, and I believe there are still reasons why a researcher might use a different curve to address specific issues with their data -- for example, if it's known that the marine environment they're working with has different characteristics, the INTCAL curve might not give the best results.

I'm out of time for now (house guests) but will get back to the rest of your comments as soon as I can -- tonight or tomorrow, I hope. Mike Christie (talk - contribs - library) 11:03, 13 July 2014 (UTC)

3) I noticed that you have "tree-ring(s)" hyphenated in Radiocarbon dating#Atmospheric variation but not hyphenated in "Variations in Carbon 14 production". Perhaps you should decide which form you want to use and make them consistent. I don't know whether you want to use the unhyphenated form (two separate words) when its a noun and the hyphenated form when it is used as an adjective. @Rothorpe: What do you think? CorinneSD (talk) 21:21, 10 July 2014 (UTC)

Yes, strictly hyphen for adjective, no hyphen for noun phrase. Rothorpe (talk) 21:43, 10 July 2014 (UTC)

Agreed; fixed. Mike Christie (talk - contribs - library) 00:59, 11 July 2014 (UTC)

4) In the second paragraph in the section "Variations in 14C production", you have "polar excursion" (with a link). Later in the paragraph you have "polarity excursion". Is that an intended variation on the phrase? CorinneSD (talk) 21:45, 10 July 2014 (UTC)

No, it's an error; it should be "polarity" in each case. Fixed. Thanks for your comments so far -- much appreciated. Readability is a real concern with a scientific article, and I hope we can make this as accessible as possible. Mike Christie (talk - contribs - library) 00:59, 11 July 2014 (UTC)

5) In the third paragraph in the section Radiocarbon dating#Physical and chemical background, you have a sentence that begins:

"If it is assumed that the cosmic ray flux has been constant over the last ~100,000 years,..."

This is the first time that the word "flux" is used in the article, and, I'm sorry to say, I don't know what "cosmic ray flux" means. I believe "flux" is related to the word "fluctuation", but that's just a guess. Is there any way to add a defining word or phrase? CorinneSD (talk) 15:40, 11 July 2014 (UTC)

I've wikilinked "flux"; basically it means the density, or intensity, of the cosmic rays. To say the flux has been constant means that there hasn't been any significant change in the amount of cosmic rays hitting the atmosphere. Is there a better way to say this? Mike Christie (talk - contribs - library) 01:25, 14 July 2014 (UTC)

6) If you're interested, you can see User talk:Rothorpe#Radiocarbon dating and User talk:Rothorpe#Radiocarbon dating 2, where I asked Rothorpe a few questions regarding punctuation, word order, etc. CorinneSD (talk) 15:42, 11 July 2014 (UTC)

I took a look and I agree with the changes you and Rothorpe discussed. Mike Christie (talk - contribs - library) 02:25, 14 July 2014 (UTC)

@CorinneSD: I think I've caught up with your comments now. Thanks! Mike Christie (talk - contribs - library) 02:25, 14 July 2014 (UTC)

A few more comments from CorinneSD

1) I've just started reading the rest of the article. The paragraph in the section "Impact of climactic cycles" is as follows:

Because the solubility of CO2 in water increases with lower temperatures, glacial periods would have led to the faster absorption of atmospheric CO2 by the oceans. In addition, any carbon stored in the glaciers would be depleted in 14C over the life of the glacier; when the glacier melted as the climate warmed, the depleted carbon would be released, reducing the global 14C/12C ratio. The changes in climate would also cause changes in the biosphere, with warmer periods leading to more plant and animal life. The effect of these factors on radiocarbon dating is not known.

I don't know. Maybe because I took a break from reading the article, or maybe just because of my own ignorance of the subject, I don't understand some things here. I understand the first sentence fine. In the second sentence, I don't understand:

"would be depleted in 14C".

That means nothing to me. I know carbon 14 decays over time, so there's less of it as time passes. Is that what this means? Now, if I am correct in supposing that that's what it means, then I don't understand this phrase in the next sentence:

"the depleted carbon would be released". Does that mean that the carbon stored in the glacier, a combination of carbon 14 and carbon 12, would simply at that time have less carbon 14 than it did when the water froze? Does that mean that it would have more carbon 12 in it? Does carbon 14 just disappear, or does it become carbon 12 over time? I guess I'm not clear on what "reducing the global 14C/12C ratio" means. I guess I have to go back to the beginning of the article and read all the way through again. (Are you sure you want me to read to the end of the article? :) CorinneSD (talk) 22:13, 20 July 2014 (UTC)

I now see an explanation for "reducing the...14C/12C ratio" in Radiocarbon dating#Hard water effect. CorinneSD (talk) 22:25, 20 July 2014 (UTC)

I see that phrase "depleted in 14C" again in the section Radiocarbon dating#Hemisphere effect. I'm wondering if it would be clearer if you used the preposition "of" instead of "in" for this particular phrase: "depleted of 14C". That "depleted in" doesn't make any sense to me. CorinneSD (talk) 22:30, 20 July 2014 (UTC)

By "depleted in 14C" I mean that the amount of 14C in the article has been reduced by some amount. To me, "depleted of 14C" would imply that there was no 14C left at all -- it would be short for "depleted of all 14C", whereas I read "depleted in 14C" as short for "depleted with respect to 14C". It looks like from your subsequent comments that you now understand the paragraph, but just to be sure, here's an explanation. The 14C in the glaciers (in dissolved carbon dioxide) decays over time, turning into nitrogen. After, say, 5,000 years, half the 14C in the glaciers is gone. Then when the glaciers melt, the carbon dioxide in them is released back into the atmosphere. The atmosphere still has the expected ratio of 14C to 12C, because cosmic rays were continuing to make 14C while the glaciers were frozen. The melting glaciers release carbon dioxide that has a lower ratio of 14C/12C back into the atmosphere; this lowers the 14C/12C ratio of the whole atmosphere. That would have an impact on the apparent age of something -- a piece of wood from that time might appear to be older than it really is, because it would have this "old carbon" from the glaciers in it. Mike Christie (talk - contribs - library) 01:35, 21 July 2014 (UTC)

You know I'm not a scientist, but I wonder about two things regarding the Radiocarbon dating#Island effect:

1) You have a separate section for "Island effect" but then discount it with one example. You don't mention whose idea the island effect was, or is, or whether any scientists think it does exist. Why mention it if your one example proves it not to exist? I think more than one example is needed.

I've been wondering whether to just delete that section, since the net result is that there is no island effect. Still, the sources mention it, so I think I need to. The sources I have, which are mostly survey works, don't give the originator of the idea. I'll add it if I'm able to find out who came up with it, but I don't think it's really necessary. I don't know if there are any other experimental refutations of the island effect -- the example given is the only one covered in the sources. Mike Christie (talk - contribs - library) 01:35, 21 July 2014 (UTC)

2) I wonder whether the results of that experiment with Seattle and Ireland would have been different if the island were farther from England and the European mainland. What if they had chosen Iceland, or Hawaii -- another island in the northern hemisphere that was farther from any continent? CorinneSD (talk) 22:38, 20 July 2014 (UTC)

Good question, but not one I can answer in the article -- that really would be original research! Mike Christie (talk - contribs - library) 01:35, 21 July 2014 (UTC)

2) In the section Radiocarbon dating#Sample material considerations, in the last bulleted item, would you consider changing "Other types of sample" to either "Other sample types" or "Other materials"? While "other types of sample" is not wrong, it's a little stilted, and the other phrases, because shorter, are more concise, and they are more common. CorinneSD (talk) 23:02, 20 July 2014 (UTC)

I agree; I've changed it to "Other materials". Mike Christie (talk - contribs - library) 01:54, 21 July 2014 (UTC)

3) In the section Radiocarbon dating#Preparation and sample size, I see several commas that I think are not necessary (again, it's a question of style and an individual choice, but I tend to use commas only when necessary):

"Particularly for older samples, it may be useful to enrich the amount of 14C in the sample before testing. This can be done with a thermal diffusion column. The process takes about a month, and requires a sample about ten times as large as would be needed otherwise, but it allows more precise measurement of the 14C/12C ratio in old material, and extends the maximum age that can be reliably reported."

In the third sentence, I would take out the comma after "take about a month" and the comma after "old material". These commas are unnecessary and slow down the flow of the sentence. The sentence would then look as follows:

"The process takes about a month and requires a sample about ten times as large as would be needed otherwise, but it allows more precise measurement of the 14C/12C ratio in old material and extends the maximum age that can be reliably reported." CorinneSD (talk) 23:12, 20 July 2014 (UTC)

Mike, I saw some more unnecessary commas in the next paragraph, so I decided to go ahead and edit the entire section. Hope you don't mind. (Feel free to undo or change.) As you'll see, I really revised the last paragraph. I felt that the sentences did not flow well the way it was worded. The only problem I see is that at least one of the two testing technologies was mentioned in a paragraph just above this one. Usually, the first time a term appears in an article is when it is linked. Other than that minor issue, you may or may not mind the introduction of the two testing technologies here (rather than earlier). CorinneSD (talk) 23:29, 20 July 2014 (UTC)

I looked through your edits and agree with all of them; you're particularly good at spotting superfluous commas, which I have a weakness for. Thanks for the edits. Mike Christie (talk - contribs - library) 01:54, 21 July 2014 (UTC)

Arbitrary section break

4) I have several questions regarding the section Radiocarbon dating#Beta counting. (I know that to you these things might seem obvious, but to me they are not. I thought you might like to know the places where I get confused or feel that something is not clear.):

1) In the first paragraph, it's not made clear where the sample is actually placed. Also, just for my own interest if not for the article, could you tell me the reason for the carbon coating on the inside of the cylinder?

I can see this isn't clear; that carbon is the sample. I've reworded to clarify this. Mike Christie (talk - contribs - library) 23:33, 21 July 2014 (UTC)

It's much clearer now. Good work! CorinneSD (talk) 02:19, 22 July 2014 (UTC)

2) The first sentence of the second paragraph mentions "bomb carbon". Is this related to the second paragraph in Radiocarbon dating#The Effects of human activity? If so, and the reader fails to make the connection, this might be confusing. Perhaps a little reminder of what it refers to would help. If not, then what is it?

Yes, that's what is meant. I use the phrase "bomb carbon" in that paragraph, but it's a long way back, so I've added a parenthetical explanation. Mike Christie (talk - contribs - library) 23:37, 21 July 2014 (UTC)

3) The fourth paragraph begins, "For both types of counter". Now I know you know this refers to gas proportional counters and liquid scintillation counters, but just before this, at the end of the third paragraph, you mentioned anticoincidence counters. I think for the sake of clarity, you should mention the names of the two types of counter:

"For both the gas proportional counter and liquid scintillation counter,...".

Agreed; done. Mike Christie (talk - contribs - library) 23:37, 21 July 2014 (UTC)

4) In the middle of the fourth paragraph you switch to future tense ("will also be used"). Since you have been using present tense throughout, I think you should stay in present tense. Present tense is appropriate for something that is done on a regular basis. It's part of the procedure. Also, although you didn't mention it, I assume the testing of a blank sample is normally done before the real testing begins. You could incorporate this order in your sentence. (And is the testing of a sample with standard activity also done before the real testing begins?) Regardless of whether you mention the order of these tests, I still think present tense is best.

Agreed; I changed this to present tense. The order isn't specified in the source I used, and I don't think it would matter. Mike Christie (talk - contribs - library) 01:59, 22 July 2014 (UTC)

5) Toward the end of the fourth paragraph, you use the phrase "original sample" again (you will recall that we discussed this earlier). It's not completely clear what "original sample" means. Would you consider using a different phrase? CorinneSD (talk) 16:23, 21 July 2014 (UTC)

Reworded; is that better? Mike Christie (talk - contribs - library) 02:20, 22 July 2014 (UTC)

Yes. It's much better. I'm wondering whether the sentence would be even clearer if you added the adverb "solely" after "due":

"This provides a value for the background radiation, which must be subtracted from the measured activity of the sample which is being dated to get the activity due solely to that sample's 14C".

CorinneSD (talk) 02:42, 22 July 2014 (UTC)

Done. Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

5) I just started reading the section on Radiocarbon dating#Accelerator mass spectrometry and I found one issue in the first sentence:

1) The first sentence reads:

"AMS counts the atoms of 14C and 12C atoms in a given sample,..."

Do you really want the word "atoms" twice in this sentence?

No, that's debris from an earlier form of the sentence, I think. Fixed. Mike Christie (talk - contribs - library) 02:20, 22 July 2014 (UTC)

2) In this phrase, "negatively charged C- ions", do you need to use the minus sign after "C" when you are saying that they are negatively charged? Could you write "negative charged carbon ions"?

I thought about this and would like to leave this as is. A positively charged C³⁺ ion isn't the same as a positively charged C⁺ ion, after all, so the minus sign does add information. I could drop "negatively" without loss of precision, but I think it helps the less technical reader confirm that they understand what they're reading. Do you have any suggestions for another way to phrase this? Mike Christie (talk - contribs - library) 02:20, 22 July 2014 (UTC)

Well, what I was thinking before, but didn't write, was first use the phrase "negatively charged carbon ions" and then put "C-" in parentheses after it, or after "carbon". CorinneSD (talk) 02:46, 22 July 2014 (UTC)

I rephrased this to include an explanation of "ion". How's that? Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

3) The last sentence in the first paragraph in this section reads:

"AMS is more sensitive than beta counting, and can date samples that contain only a few milligrams of carbon, such as individual seeds."

When I read this sentence, it sounded familiar. The last sentence in the section Radiocarbon dating#Preparation and sample size reads:

"AMS labs are much more sensitive and can deal with samples as small as 10 milligrams (for charcoal) and generally require less than a gram of most sample materials."

:While not exactly the same, these two sentences are quite similar. I wonder whether you care to choose the most appropriate place for the information and delete the other one. CorinneSD (talk) 16:44, 21 July 2014 (UTC)

Done; I removed the second occurrence. Mike Christie (talk - contribs - library) 02:23, 22 July 2014 (UTC)

6) The second paragraph in the section Radiocarbon dating#Accelerator mass spectrometry begins:

"The use of AMS, as opposed to simpler forms of mass spectrometer,..."

You have already made clear (in the middle of the section Radiocarbon dating#Measurement) that AMS stands for "accelerator mass spectrometry". So, actually, here you are saying:

"The use of accelerator mass spectometry, as opposed to simpler forms of mass spectrometer,..."

I think the two terms should be parallel. Since you can't change AMS, you should probably change "mass spectrometer" to "mass spectrometry".

I see you've already made this change, and I agree with it. I don't know if you noticed, but the first occurrence of "AMS" in the article (here) appears to refer to "accelerator mass spectrometer", rather than "accelerator mass spectrometry"; the form of that sentence makes it difficult to change. I'm inclined to leave it as it is, but if you can see a way to improve it that would be great. Mike Christie (talk - contribs - library) 02:40, 22 July 2014 (UTC)

Well, in the third paragraph of the lead I found "accelerator mass spectrometry", with a link. Maybe you could put the initials "AMS" in parentheses after it. Then you wouldn't need "(AMS)" after "accelerator mass spectrometer" later. When scientists use the initials "AMS", aren't they usually referring to the method rather than the instrument? CorinneSD (talk) 02:54, 22 July 2014 (UTC)

I don't want to put the abreviation in the lead, because it's not used till much later in the article. I tweaked the "Preparation and sample size" section to make AMS stand for the method, not the device; I think that fixes it. Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

7) In the second paragraph in this section, you describe the necessary testing of two different kinds of blank sample. I also saw a brief mention of both tests just two paragraphs earlier -- the last paragraph in Radiocarbon dating#Beta counting. Do you really feel both are needed? If do you, perhaps the first mention of the tests could be briefer.

I just noticed that the second instance has "a blank sample and a standard sample"; in fact in AMS two kinds of blank are used, as the paragraph goes on to make clear, so I made these plural, which since it's a general discussion avoids the question of how many are used. To your point: I've cut part of the sentence and made an associated tweak. Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

8) In the middle of the second paragraph in this section, you have a sentence that reads:

"Two different kinds of blank may be measured: a sample of dead carbon that has undergone no chemical processing, in order to detect any machine background, and a sample known as a process blank made from dead carbon that is processed into target material in exactly the same way as the sample itself."

You have the word "sample" three times. The first two instances are clear. The third one is not. I believe the third one refers to the real sample of which one is trying to determine the age through radiocarbon testing, but it's not clear. It could refer to one or the other of the two samples just mentioned. Is there a way you could make this clear (without using "original sample")?

Changed to "sample being dated". Mike Christie (talk - contribs - library) 22:22, 22 July 2014 (UTC)

9) In that same section, you have the following sentence:

"Any 14C signal from the machine background blank is likely to be caused either by beams of ions that have not followed the expected path inside the detector, or by carbon hydrides such as 12CH2 or 13CH."

Now, this will really show my ignorance, but here goes, anyway:

(a) Why are there any beams of ions passing through the detector if there is no 14C in this piece of dead carbon being tested? Why is there an "expected path" if there are no 14C ions in this sample?

The beams of ions are formed of whatever is in the sample. The C^- ions are not just 14C -- they're 14C, 13C and 12C, in whatever proportion exist in the sample being dated. So even if there are no 14C atoms in the sample at all, there will still be a beam of ions formed of the 13C and 12C atoms. Is there a way to make this clearer in the article? Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

(b) Why would there by carbon hydrides in the detector? CorinneSD (talk) 17:06, 21 July 2014 (UTC)

The source doesn't specify. I believe it's because it's never possible to have the sample completely pure, and with AMS, counting individual atoms that may only constitute one part int 20 million of the sample, even the tiniest impurities would have a huge impact on the measurement if they happen to have the same atomic weight as 14C. I don't think I should add anything to that effect without an explicit source, though. Mike Christie (talk - contribs - library) 09:53, 22 July 2014 (UTC)

That's all I can do now. I just read the "Calculations" section. I need a little more time to get through the rest of the article. I'll get to it either later today or tomorrow. CorinneSD (talk) 17:47, 21 July 2014 (UTC)

Arbitrary section break 2

1) The second-to-last paragraph in the section Radiocarbon dating#Calibration begins:

"When several radiocarbon dates are obtained for samples which are known or suspected to be from the same object, they may be able to be combined."

There is some ambiguity in the pronoun "they". It could refer to "dates" or "samples". The sentence would be clearer if you used a noun instead of the pronoun: "the dates" or "the samples".

Also, even though "may be able to be combined" is not wrong, it is a little tortured. You might consider re-wording this so that the verb is simpler, something like "it is possible to combine the..." or "the...can be combined".

I made this "it may be possible to combine the measurements to get a more accurate date"; I think that addresses both of your points. Mike Christie (talk - contribs - library) 10:04, 22 July 2014 (UTC)

Yes, I saw that. Very good. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

2) In the first bulleted list in the section Radiocarbon dating#Reporting dates, in the third item is the phrase "at 1 σ confidence". (I don't know what that symbol/letter after the 1 is or what it's called.) In all other instances of this "1 σ" in the article, there is no space between the "1" and the "σ". Here, you have a space. I didn't know if this was deliberate or not. Just thought I'd point it out.

It's a mistake; I've cleaned it up. That symbol is a Greek letter, sigma; I've added a brief note to that effect when it first appears, in the "Errors and reliability" section. Mike Christie (talk - contribs - library) 10:04, 22 July 2014 (UTC)

I saw that, too. Good. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

3) In this same section, Radiocarbon dating#Reporting dates, last sentence, you have the word "pretreatment". It comes out with a red squiggly line under it in edit mode, indicating that the software does not recognize the word, or has some problem with the spelling. I don't know if it is accepted as one unhyphenated word or not (even the words "unhyphenated" and "bulleted" come out with a red squiggly line under them). Just thought I'd point it out.

I see it unhyphenated in the sources, so I think it's OK. Mike Christie (talk - contribs - library) 10:15, 22 July 2014 (UTC)

O.K. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

4) That same last sentence begins:

"In addition, a recommendation for reporting calibrated dates published in 2014 suggests...."

"A recommendation...suggests..." is a little odd. To recommend and to suggest are almost synonyms, and a recommendation and a suggestion are almost synonyms. You might tighten up the language by saying who suggests/recommends something, or where the suggestion/recommendation comes from or is found:

• X recommends that...
• X suggests that...
• It was recommended that... / It has been recommended that...
• It was suggested that... / It has been suggested that...

(etc.) (I think "recommends" or "recommended" is best.)

I changed this to "In addition, an article in Radiocarbon in 2014 about radiocarbon date reporting conventions recommends that..." Does that work? Mike Christie (talk - contribs - library) 10:15, 22 July 2014 (UTC)

Yes. Much better. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

3) In the first paragraph of the section Radiocarbon dating#Interpretation, a sentence begins:

"In these cases a date for the coffin or charcoal is indicative of the date deposition of the grave goods...."

I had never seen the phrase "the date deposition". Shouldn't this be "the date of deposition"?

Oops. Yes; fixed. Mike Christie (talk - contribs - library) 10:15, 22 July 2014 (UTC)

4) Also in the first paragraph is the following sentence:

"These improved field methods were sometimes motivated by an endeavour to prove that a 14C date was incorrect."

I would just like to suggest the substitution of the word "attempts" for "an endeavour". I think it conveys the actual events better, and I think it probably happened more than once, so the plural is probably preferable, but if you don't like the plural, then use "an attempt". Then the sentence would read:

"These improved field methods were sometimes motivated by attempts to prove that a 14C date was incorrect", or

"These improved field methods were sometimes motivated by an attempt to prove that a 14C date was incorrect."

"Attempts" works for me; done. Mike Christie (talk - contribs - library) 10:15, 22 July 2014 (UTC)

5) In the second paragraph in this same section is the following sentence:

"It is not always possible to recognize re-use, if no such signs are present."

There is no mention of specific signs before this. I suppose it refers to whatever signs indicated that the wood of the trackway had been re-used, but that's a mental connection that the reader has to make. I'm wondering whether that clause, "if no such signs are present", is really necessary. Either delete it or add a few words to the clause to clarify "signs", something like,

• if no obvious signs are present, or
• if no clearly discernible signs are present, or
• if there are no clearly discernible signs, or
• if there are no obvious signs.

I deleted it; you're right that as it stands it requires a mental connection, and after thinking about it I feel it doesn't need any qualifying clause. Mike Christie (talk - contribs - library) 10:42, 22 July 2014 (UTC)

I agree. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

6) In the second paragraph in the section Radiocarbon dating#Impact on archaeology is the following clause:

"it became apparent that these innovations must sometimes have arisen from local causes."

I'm just wondering whether "must sometimes have arisen from local causes" is the right phrase. You haven't been discussing causes of innovation, you've been discussing sources of innovation -- "diffusion through the continent, or by invasions of tribes" who brought new ideas with them. Causes and sources are a bit different. It's more about routes and places where innovations arose. Perhaps, instead of "must...have arisen from local causes", you could use "must...have arisen locally", or "must...have arisen from within the local culture".

Excellent point. I went with "must sometimes have arisen locally". Mike Christie (talk - contribs - library) 10:42, 22 July 2014 (UTC)

I saw that. I think your choice of the shorter option in both this and the previous item is excellent. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

Well, I reached the end of the article, and I learned a lot. Thank you for your patience with my ignorance of the science.

I have two more thoughts:

1) In the section Radiocarbon dating#Calibration, in the paragraph right next to the CALIB output graph, there is the following clause:

"the vertical width of the curve corresponds to the width of the standard error in the calibration curve at that point."

You lost me here. I don't understand "the vertical width", and I don't understand which curve of all the curves in the graph is being referred to.

This is a complicated graph, and I'd like to make this explanation better. The fat grey line that descends from upper left to lower right is the INTCAL13 curve itself. That fat grey line is the same as the area between the two dotted lines in the graph above it -- it indicates that the "true" calibration curve has a 68% chance of being inside that line. If you draw a vertical line at any point on the graph, it will go through the fat grey line. The amount of the vertical line that's actually inside the fat grey line will depend on where you draw the vertical line. Near the middle of the graph, for example, it would go through the very thin downslope of the fat grey line, and not much of the vertical line would be inside the fat grey line. That's what I meant by "vertical width": the amount of a vertical line that would be within the fat grey line at any given point. Can you suggest a better way to phrase this? Mike Christie (talk - contribs - library) 10:42, 22 July 2014 (UTC)

Thank you for this explanation. (It's quite clear in itself.) I'll take a look at it again now in this new light, and get back to you.

1) Why would you draw a vertical line? Why would you need to draw a vertical line?

2) I think, instead of using the phrase "vertical width", you should just use the word "width" and explain what you just explained above: "The amount of the vertical line that is actually inside the fat grey line will depend on where you draw the vertical line. Near the middle of the graph, for example, it would go through the very thin downslope of the fat grey line, and not much of the vertical line would be inside the fat grey line. In contrast, if one draws a vertical line through the fat grey line near the right of the graph, more of the vertical line would be inside the fat grey line."

But I still don't see what that means or represents -- what the amount of the line that is inside the fat grey line tells us.

3) Is the "histogram" the entire graph (the one with the fat grey line), or is it just the "fat grey line"? I guess that "fat grey line" is not a calibration curve.

4) I don't understand why you have input data that is a calendar year. If you don't know the date of an object, how would you have a date to put into the calculations?

5) I also don't see the connection/relationship between the kind of bell-curve with an arrow in it at the left of the graph and the rest of the graph.

This is probably amusing your fellow science editors. It's clear that this type of graph is over my head. I understand, pretty much, all the variables that are discussed in the article. I just don't understand the graphs. But, I guess that's all right. Most of your readers will probably understand them. CorinneSD (talk) 19:27, 24 July 2014 (UTC)

I think part of the confusion is probably just practice -- when you've read a lot of graphs you start to get a sense of how to read them, without needing much explanation. We can't explain everything as if a reader has never seen any graphs before, but I think if you understand all the variables, and don't follow the graph, it needs to be made clearer. Taking your questions in order:

1. There's no need for a user of the graph to draw a vertical line; I was using that as way to clarify what I meant by "vertical width". See the next answer for more. I can see that "vertical width" isn't a clear phrase, but let's defer that till you're clear on what the graph actually says.

2. The real point here is your last question -- what the amount of the line that is inside the fat grey line tells us. Here's an explanation that I hope will clarify this. A calibration curve is a graph showing the relationship between a radiocarbon age measured for some object, and the calendar age of that object. The way you use the curve is by plugging in a radiocarbon age (on the vertical axis), reading across, and then finding the corresponding calendar age. But the way that researchers actually construct the curve is the reverse of that -- they take an object of known age, and read across the horizontal axis to find that age, then they measure its radiocarbon age, and go up and put in that data directly above that point on the horizontal axis. So let's say they take an object they know dates from 770 AD. They measure the radiocarbon age, and they get 1260 BP. But their measurement is not perfect -- the result they get is really a bell curve, with 1260 BP in the middle. There's a 68% chance (this is the 1σ range, mentioned in the article) that the result is within 13 years of that date: in other words, there's a 68% chance that an object from 770 AD will give you a radiocarbon age between 1273 BP and 1247 BP. So they go to 770 AD on the horizontal axis, and draw a line from 1273 to 1247 BP. That's the "vertical width" of the fat grey line at that point. The fat grey line is the collection of all the vertical lines they draw by measuring radiocarbon for all the different ages on the horizontal axis. The fat grey line is the calibration curve; it's fat because it's drawn to have 68% confidence that it includes the true number.

3, 4 & 5 are best answered together. The input data (1270 BP in the text) is a radiocarbon age, not a calendar year. I don't think the text makes that clear enough. First, assume that you have a sample of old wood and you've taken it to a radiocarbon lab, and they've told you that the age is 1270 +/1 10 years BP, in radiocarbon years. Now you want to know what that means in calendar years. That's what the CALIB graph shows: how you put in a radiocarbon age and get out a calendar age. There are three parts to the graph. First, the bell curve that is sideways on at the left side is the input data. It represents the lab results. The centre of that bell curve is at 1270 BP; the dark grey section is 1260 BP to 1280 BP -- it corresponds to the +/- 10 years that the lab quoted. (The lab quotes the 68% confidence level.) So we have 68% confidence that the piece of wood is between 1280 and 1260 BP in radiocarbon years. The second part of the graph is the calibration curve -- the fat grey line. Read across from the dark grey section of the input data, and you'll see it intersects the calibration curve at three separate points. Those are three different points where the researchers who constructed the calibration curve found samples that would give a radiocarbon age in that range. Now run your eye straight down from each of those three points in turn to the bottom of the graph. On the horizontal axis you'll see another, irregular, graph. Each of the three parts of the calibration curve that the input data intersects with is directly above a dark grey part of the result curve at the bottom. That curve shows information about how old (in calendar years, since this is the horizontal axis) the sample of wood is. So the curve converts input data (left axis) to output data (bottom axis). In the output curve, dark grey means 68% confidence, just as before, so it is saying that with 68% confidence the wood dates from either 690-720 AD, 740-750 AD, or 760-765 AD. Mike Christie (talk - contribs - library) 01:07, 25 July 2014 (UTC)

2) I saw the INTCAL13 curve in Radiocarbon dating#Calibration. I believe the one shown is for the northern hemisphere. ("The INTCAL13 data includes separate curves for the northern and southern hemispheres, as they differ systematically because of the hemisphere effect; there is also a separate marine calibration curve.") I thought it would be interesting to see the curves for the southern hemisphere and for marine samples for comparison. I think readers who live in the southern hemisphere would find that curve particularly interesting. Would it be possible to provide all three curves, and place them near each other? CorinneSD (talk) 02:19, 22 July 2014 (UTC)

It would, but I don't think it would be helpful to show the complete graphs -- at the scale of 50,000 years across the horizontal axis, I don't think it would be possible to distinguish them for most of their range. It might be possible to take a small range -- say, 1,000 to 2,000 before present -- and give the three graphs over that range, to illustrate that they differ. However, I'm also a bit concerned that the calibration section is a bit long and complex; Jim Bleak, above in this PR, suggested moving it to a subarticle. Hence I'm a bit loath to actually add to this section. What do you think? Mike Christie (talk - contribs - library) 10:42, 22 July 2014 (UTC)

Let me look at the Calibration section again before I reply. CorinneSD (talk) 22:59, 22 July 2014 (UTC)

Arbitrary section break 3

Mike, I decided to go back to the beginning of the article on Radiocarbon dating and read it through once more. I was stopped by the very first line:

"Radiocarbon dating is a dating method that uses radiocarbon, or 14C, a radioactive isotope of carbon."

I feel that "Radiocarbon dating is a dating method" is not especially elegant writing. You've got "dating" twice, and "a dating method" without any hint of what is to be dated with this method is at one and the same time vague and ambiguous.

I'm wondering whether the sentence could be re-worded to give just a slight indication of what the method is applied to, something like this:

"Radiocarbon dating is a method that uses a radioactive isotope of carbon to assign a date to a man-made or natural object or material from the past".

Then you could introduce 14C, and "radiocarbon", in the next sentence. Or, if not that, then perhaps:

"Radiocarbon dating is a method for determining the date of a man-made or natural object or material from the past. The method uses radiocarbon, abbreviated 14C, a radioactive isotope of carbon.

I think with something like this, a reader would be more intrigued and want to continue reading. What do you think? CorinneSD (talk) 23:24, 22 July 2014 (UTC)

My daughter (aged 19, studying physics) read the first part of the article this evening; she burst out laughing at the first sentence because of the repetition of "dating". So I think you're right to object to it! I looked at your version and worked with it some more; I've now changed it to "Radiocarbon dating is a method of determining the age of an object by using the properties of radiocarbon, a radioactive isotope of carbon", and tweaked the third sentence to introduce the 14C abbreviation. What do you think? Mike Christie (talk - contribs - library) 02:01, 24 July 2014 (UTC)

2) Mike, you're going to say, "Oh, no" with these additional comments. Tell me if you want me to leave off adding more comments.

Not at all! Your comments are very helpful. Mike Christie (talk - contribs - library) 02:01, 24 July 2014 (UTC)

The second paragraph in the lead begins,

"Although the idea behind radiocarbon dating is straightforward, it depends on many assumptions."

I have two points I want to make about this:

1) To a non-scientist, the word "assumptions" has very little meaning -- almost no meaning. 2) If you read the rest of the paragraph, you will see that you don't refer to assumptions again. This leaves the use of "assumptions" in the first sentence exactly what I told you: no meaning -- an empty word taking up space.

This is a good sentence. If you want to keep the sentence, I suggest the word "variables", and perhaps "variables that must be taken into consideration". Then you can mention some of the variables (in simple language). That might be a kind of overview that Johnbod was talking about (haven't decided whether you need a separate overview section or not). The rest of the paragraph -- with the exception of the very next (second) sentence -- kind of mention the variables.

There is a bit of a problem with this paragraph. In the first sentence you are getting into the very beginning of explaining the method. In the second sentence, you start to talk about the history of the development of the method. The juxtaposition of these two sentences creates a lack of cohesion. Then you begin to discuss the variables that must be considered. I think the history needs to be kept separate, or the order of sentences needs to be changed. Do you see what I mean? CorinneSD (talk) 23:39, 22 July 2014 (UTC)

I think a list of some of the variables in simple language would actually intrigue a reader.

The rest of the lead is pretty good. I wouldn't get into the history of the technique in the lead. I would remove this from the lead:

"The development of the technique required much additional work".

I've changed the first two sentences of this paragraph to "The idea behind radiocarbon dating is straightforward, but the development of the technique required much additional work. Research has been going on since the 1960s to determine what the proportion of in the atmosphere had been over the past fifty thousand years." I take your point about "assumptions", so I've cut that part. I left in "required much additional work", though I'm open to changing the phrase: I think it's worth letting the reader know that there was a long journey from the original idea to a workable dating method, including the discovery of problems such as fractionation and reservoir effects. Now that I've removed the mention of assumptions, does this work better? I also changed the start of the second sentence to make it a more direct reference to the work that had to be done. What do you think? Mike Christie (talk - contribs - library) 10:21, 24 July 2014 (UTC)

Regarding the brief section on archaeology in the lead, can you avoid using "synchronization"? CorinneSD (talk) 23:44, 22 July 2014 (UTC) CorinneSD (talk) 23:49, 22 July 2014 (UTC)

Revised. Mike Christie (talk - contribs - library) 10:21, 24 July 2014 (UTC)

I just took a look at the article from beginning to end (quickly). It seems to me that the Radiocarbon dating#Invention section is quite short compared to all the other sections. Is there anything interesting you could add to this section?

Yes, there's a bit more in Taylor. I'll work on that tonight. Mike Christie (talk - contribs - library) 11:06, 24 July 2014 (UTC)

Now added. Mike Christie (talk - contribs - library) 20:05, 26 July 2014 (UTC)

Also, it seems, just in terms of length, that the Radiocarbon dating#Calibration section is much longer than the other sections. I know this would be a difficult section to cut down, but, besides being long, it's also very technical. I'm wondering whether you would considering making just a short section for calibration and then creating a separate article. It's not absolutely necessary. There are other technical sections, like "Fractionation". It's really your choice.

I've been thinking for a while that calibration deserves its own article. I'll think about this some more. Mike Christie (talk - contribs - library)

I think more examples of the use of radiocarbon dating in the section Radiocarbon dating#Impact on archaeology might be interesting for the reader. Would you consider changing the name of that section to "Use of the method in archaeology", or "Application to archaeology", or something like that? CorinneSD (talk) 23:58, 22 July 2014 (UTC)

In my mind, impact and use are different things -- I meant the section to be about the way radiocarbon dating has transformed archaeology, in many different ways. The "reporting dates" and "interpretation" sections were meant to be the ones about how the technique is used in practice. I do have more examples; Walker has several good ones, I believe. How about putting all three of these sections into a new section, "Application to archaeology", as lower level headings? Then I could add an "examples" section before the "impact" section. What do you think? Mike Christie (talk - contribs - library) 11:06, 24 July 2014 (UTC)

Before I answer your question about whether to move the "reporting dates" and "interpretation" sections to a new archaeology section, I need to ask you whether the radiocarbon dating method/ technique is used for anything other than archaeology. If it is, then maybe they don't belong in an archaeology section. Maybe the overarching section needs a different name such as "Practical uses of the radiocarbon dating method", with archaeology as a sub-heading under that. Then "reporting dates" and "interpretation" can go under "Practical uses", too.

If the radiocarbon dating method is used primarily in archaeology, then an archaeology section makes sense, with "reporting dates", "interpretation", and "impact on the field of archaeology" (or something) as sub-headings. Other uses of the method could be mentioned in a separate section. CorinneSD (talk) 19:34, 24 July 2014 (UTC)

It is used outside archaeology; I just did a quick search and found a reference talking about uses in hydrology, climatology, meteorology, ecology, geology and oceanography. I think archaeological radiocarbon testing is the vast majority of work at the labs -- I would guess 90 or 95%, but I don't know. I'll think about this some more; you're right that I can't have this information presented as if it is confined to archaeology.

I'm out of time again; I don't know how much time I'll have tomorrow, but I should have some over the weekend, so more replies then. Mike Christie (talk - contribs - library) 01:15, 25 July 2014 (UTC)

I think if you work just a little more on the lead section, you won't need an overview section. I think this subject is the kind of subject that you can't talk about half-way, in half measures. You either speak about it in general terms (the lead) or, once you get into it, you have to use the technical language and explain the details and how they all relate to each other (as you have done, quite well). It would be very difficult to write an overview that summarizes all the information you have in this article. I think you could refine the lead a little bit and that would suffice. (Are overviews after the lead common in science articles on WP?) CorinneSD (talk) 00:02, 23 July 2014 (UTC)

I haven't seen overviews after the lead section that I can recall, but I don't think that means much. If you can think of further ways to improve the lead, let's do that, then revisit the question of whether an overview is needed. Mike Christie (talk - contribs - library) 11:06, 24 July 2014 (UTC)

Arbitrary section break 4

(I started a new section just to make it easier. I will still add replies in the previous section.)

1) I read the revised first few sentences of the lead. I just wonder about the word "soon" in "soon became a standard tool for archaeologists". Radiocarbon dating was invented in the 1940s. In the section Radiocarbon dating#Impact on archaeology, there is no indication that the method was used in archaeology in the 1950s or 1960s. Will you be adding more information about those decades in "Impact on archaeology"?

I took a look at Taylor (1987) which has some detailed early history, and I think "soon" is justified. I agree this needs to be reflected in the main text; I'll add something to the "Impact on archaeology" section. Mike Christie (talk - contribs - library) 11:22, 25 July 2014 (UTC)

Now done. Mike Christie (talk - contribs - library) 15:00, 26 July 2014 (UTC)

2) Regarding the first sentence in the second paragraph of the lead,

"The idea behind radiocarbon dating is straightforward, but the development of the technique required much additional work",

I'd like to propose two changes:

(a) change "much additional work" to "years of additional work"; and

(b) re-word the sentence as follows:

"While the idea behind radiocarbon dating is straightforward, the development of the technique required years of additional work."

If you don't like "while", then "although" or "though" would be alternatives.

(c) I think the addition of a little more would fill out the sentence:

"While the idea behind radiocarbon dating is straightforward, the development of the technique to the point where accurate dates could be obtained required years of additional work", or,

alternatively,

"While the idea behind radiocarbon dating is straightforward, years of additional work were required to develop the technique to the point where accurate dates could be obtained".

I like the last version you give above and have switched to that. Mike Christie (talk - contribs - library) 11:22, 25 July 2014 (UTC)

3) In the next sentence:

"Research has been going on since the 1960s to determine what the proportion of 14C in the atmosphere had been over the past fifty thousand years",

you're using the past perfect progressive tense ("had been going on") where there is no need to. You haven't mentioned any other event or specific time in the past that the research preceded. I'm not sure why it is important to say "since the 1960s" -- I guess this particular research started in the 1960s. May I suggest something like this:

"Starting in the 1960s, researchers worked to determine what the proportion of 14C in the atmosphere had been over the past fifty thousand years".

If you could add to that sentence something that indicates why it was important to know that, or how that helped refine the radiocarbon dating method, I think it would be helpful. CorinneSD (talk) 19:00, 24 July 2014 (UTC)

That's all I have time for this morning, but I'll just mention here that I it wasn't till about 1960 that it became clear that radiocarbon ages were not the same as calendar ages, and a calibration curve would be needed. I thought there was something to this effect in the article -- I'll look tonight or tomorrow. Mike Christie (talk - contribs - library) 11:22, 25 July 2014 (UTC)

I had another look at this and I'm not quite sure what the problem is. I used "has been going on" in the first part of the sentence because the research is still going on, and isn't going to end -- it's an ongoing research project to improve the INTCAL curves. I didn't want to say "research began" or "started" in the 60s because I wanted to emphasize that it's still going on now. Can you explain again what the problem is? Mike Christie (talk - contribs - library) 17:44, 26 July 2014 (UTC)

I am very sorry. I guess my eyes are not as good as they used to be, or I was tired after doing a lot of reading, and I mis-read that sentence. I thought it said "had been going on", and I see now that it said "has been going on", which is fine. CorinneSD (talk) 01:59, 27 July 2014 (UTC)

4) I have a few questions about the section Radiocarbon dating#Variations in 14C production, specifically these sentences:

"The known fluctuations in the earth's magnetic field strength match up quite well with this oscillation: cosmic rays are deflected by magnetic fields, so when there is a lower magnetic field, more 14C is produced, leading to a younger apparent age for samples from those periods. Conversely, a higher magnetic field leads to lower 14C production and an older apparent age".

(a) I think the phrase "in the earth's magnetic field strength" is a little long with three adjectives before the noun. I would change it to "in the strength of the earth's magnetic field".

Yes, better. Done. Mike Christie (talk - contribs - library) 17:44, 26 July 2014 (UTC)

(b) I thought that strength was normally described with adjectives like "weak" and "strong", with the comparative forms "weaker" and "stronger". Are these not normally used to describe the earth's magnetic field? You have used "lower" and "higher". I defer to your knowledge of standard language in your field, but I just wanted to point out that you also use "lower" later in the sentence to describe 14C production.

You're right; "stronger" and "weaker" are more usual. Fixed. Mike Christie (talk - contribs - library) 17:44, 26 July 2014 (UTC)

5) In the second paragraph in Radiocarbon dating#Variations in 14C production are the following sentences:

"These global geomagnetic reversals, and shorter, often localized polarity excursions, would have had a significant impact on global 14C production, since the geomagnetic field falls to a low value for thousands of years".

Are you saying here that both the global geomagnetic reversals and the localized polarity excursions would have had significant impact on global 14C production because the [global] geomagnetic field falls to a low value for thousands of years?

I don't know, but I think something is wrong with this sentence.

Also, why is only the period of low value significant? Isn't it the fluctuation itself that is more significant?

This next thought is just something to think about. Perhaps a bit nitpicky. I'll let you decide. The phrase "falls to a low value" to describe the earth's magnetic field seems like an unnecessarily vague phrase when before you had used "lower magnetic field" and "higher magnetic field" (perhaps to be changed to "weaker" and "stronger"?). What does "falls to a low value" mean? Does it mean just "becomes weaker and stays weak for a period of time"? What's the "value"? I know you know what it means, but some readers might wonder. CorinneSD (talk) 21:49, 24 July 2014 (UTC)

The references I have don't go into a lot of detail on this, but here's my understanding. The term "geomagnetic reversals" is used for a complete and long-lasting flip of the earth's magnetic field. During the time when the flip is occurring, the magnetic field is a lot weaker, and this causes increased cosmic ray penetration and hence inreased 14C production. This is a global event with long duration. A polarity excursion can be local or global; the discussions of local events appear to refer to changes in magnetic field that only affect part of the globe. A global polarity excursion seems to refer to a "quick flip to and fro". (Aitken (1990), p. 69). Local excursions are thought to have little overall impact on the 14C levels in the atmosphere. Reversals and global excursions are both global events and do have an impact on the global production of 14C.

I agree with your suggested rewording and have made that change. Mike Christie (talk - contribs - library) 17:44, 26 July 2014 (UTC)

Thank you so much for this explanation and the longer explanation of the graph, above. Regarding this explanation, do you mind if I ask you one or two more questions? You write, "During the time when the flip is occurring, the magnetic field is a lot weaker..." Then you write, "This is a global event with longer duration". When the flip occurs, does the flip -- the actual change to the other direction -- take a long time? I should think that would not take a long time. I thought the period of time while the magnetic field is in the other direction lasts for quite a while ("long duration") before changing back. So I don't understand, "This is a global event with long duration". (What, exactly, is the global event "with long duration"? The flip, or the magnetic field actually in the other direction?

Thank you for explaining "a global polarity excursion". I didn't remember reading that in the article, though. Did you say in the article that "a polarity excursion can be local or global"? Do you think it would help clarify the topic to include some of what you just wrote, above?

I've rewritten that paragraph, and I hope it's now clearer; let me know what you think. Mike Christie (talk - contribs - library) 10:50, 27 July 2014 (UTC)

Regarding your long and careful explanation of the graph, I understand the graph much better now. I don't know if you think some of what you wrote could be included in the article, particularly the two points:

1) the way the graph is read and used is the opposite direction from the way it was created by scientists, and that the "fat grey line" is the calibration curve, and

2) that the input is radiocarbon years (which have come from a lab), and one reads the graph from left to right and then down, and the output is the calendar year(s). CorinneSD (talk) 01:59, 27 July 2014 (UTC)

I've added these points, though the graph with the fat grey line is now in the subarticle, so I haven't addressed that directly. I hope this is now clearer. Mike Christie (talk - contribs - library) 10:50, 27 July 2014 (UTC)

By the way, since I have enabled "WikEd" in the Editing section of the selections in Gadgets, I have a collection of tools (many of which I know nothing about) at the top of my edit window. To strike through text, all I have to do is to highlight the text (in edit mode) then click on the capital S with a short horizontal line through it at the top of the edit window, and click "Save". CorinneSD (talk) 02:03, 27 July 2014 (UTC)

I keep forgetting you have WikEd; it's a good tool. Have you tried using the Visual Editor? I use it almost all the time; it definitely has some shortcomings, but it works for most things, and it means you don't have to remember wiki markup syntax at all. Mike Christie (talk - contribs - library) 10:50, 27 July 2014 (UTC)

Arbitrary section break 5

1) How do you access Visual Editor? Is that something I have to enable in Gadgets?

It's in your preferences, under the Beta tab, rather than the Gadgets tab. It will add another edit button (edit beta) to your edit choices; the existing "edit" becomes "edit source". Mike Christie (talk - contribs - library) 16:06, 27 July 2014 (UTC)

Thank you for this information. CorinneSD (talk) 21:14, 27 July 2014 (UTC)

2) Regarding the following sentences:

"Geomagnetic reversals, which changes the polarity of the earth's magnetic field, would have had a significant impact on global ¹⁴
C production, since during these the geomagnetic field becomes weaker, and stays weak for thousands of years while the reversal is occurring. Shorter lived (and sometimes localized) changes of polarity, known as polarity excursions, could also have affected ¹⁴
C production",

(a) The verb "changes" does not match the subject "Geomagnetic reversals". I don't know whether you want to use the plural or the general or the general singular.

(b) You have this phrase: "since during these..."

1) If you change the subject to singular, you'll have to change "these" to "this"; and

2) "these" (or "this") by itself is a little unclear. It would be better to add the noun: "these reversals".

(c) You have the following:

"and stays weak for thousands of years while the reversal is occurring".

I'm still not clear on this (and I asked you about it a few lines above this). The clause "while the reversal is occurring" is what confuses me. I know the earth's magnetic field reverses -- what? every few hundred or thousand years -- but is the actual flip, or change to the other direction, something that takes place quickly, and then it remains in that direction for thousands of years, or does the actual flip take a long time to complete before remaining in the new direction for a long time? I think it's a question of language, specifically the meaning of the word "reversal". Is the reversal the actual movement to the other direction, like the flip of a coin from one side to the other, or is the reversal a long period of time in which the earth's magnetic field is in the opposite direction from what it was before? I don't know if I am just being slow to grasp this, or whether the language needs to be more precise. CorinneSD (talk) 15:39, 27 July 2014 (UTC)

Sorry, I didn't really answer this properly above. The source I have (Aitken 1990, pp. 68-69) says this, talking about geomagnetic reversals: "During the act of reversal the strength of the dipole field falls to a rather low value so that there is a strong enhancement of carbon-14 production; the duration is of the order of several thousand years and hence a substantial effect on atmospheric carbon-14 activity is to be expected." This is definite on the question you ask as far as geomagnetic reversals are concerned. For polarity excursions, he goes on to say: "During the millennia of radiocarbon applicability there is some evidence for one or two brief polarity excursions (a quick flip to and fro) but it is not established that these were worldwide rather than localized; only if world-wide would there have been an appreciable effect on radiocarbon activity". I don't think Aitken makes it clear here how long a global polarity excursion would spend in a state with a weak field. Given that both Aitken and Bowman say that there are no global polarity excursions in the last 50,000 years, and hence there's no impact on 14C production from polarity excursions, perhaps the sentences could be changed as follows (including your number fix, above):

Geomagnetic reversals, which change the polarity of the earth's magnetic field, would have had a significant impact on global ¹⁴
C production, since during these reversals the geomagnetic field becomes weaker, and stays weak for thousands of years during the transition. The field strengthens again as the reversal completes. Shorter lived changes of polarity, known as polarity excursions, could in theory have affected ¹⁴
C production, but no global excursions are known to have occurred within the last 50,000 years." Then a note, saying "Polarity excursions can be local but local excursions would have had no significant effect on 14C production".

How does that look? Mike Christie (talk - contribs - library) 16:06, 27 July 2014 (UTC)

Well, I think it's clearer than what was there. The first part of the text you quoted from Aitken does not make clear how long the "act of reversal" normally is. The second part of the sentence says, "the duration is of the order of several thousand years...". I suppose by "the duration" he meant "the duration of the act of reversal", but he didn't make that entirely clear. Your statement, though, is a little clearer when you write, "and stays weak for thousands of years during the transition". That phrase, "during the transition", makes it clear that the transition between the two directions of the magnetic field lasts for thousands of years. Also, the next sentence, "The field strengthens again as the reversal completes", adds additional information. (I wonder how long it takes for the reversal to complete.) I'm just curious, are you using "would have had" because you are describing the fluctuations in 14C that occurred over the millennia that are now represented in the calibration curve? ("Would have had" is conjecture about past events.) In actuality, these phenomena will continue to occur, right? I notice that in the sentences right after this you use present tense ("becomes", "stays", and "strengthens"), and then you go to "could have affected". Are you all right with these changes of tense? I'm not saying they necessarily need changing; I just wanted to point them out so you could check to be sure that's what you want. CorinneSD (talk) 21:14, 27 July 2014 (UTC)

I forgot to add, the rest of what you suggested sounds fine. Perhaps put the last sentence about polarity excursions in parentheses? CorinneSD (talk) 21:18, 27 July 2014 (UTC)

Corinne, can I tell you again how much I enjoy working on text with someone who cares about precision in syntax? It's a pleasure working with you, and I really appreciate the effort you're putting in.

I used "would have had" because we have no direct evidence of the effects, and also because I'm not talking about a specific geomagnetic reversal (since there have been none in the time period of interest to radiocarbon dating (50,000 years)). So it's a combination of counterfactual and subjunctive. Counterfactual: if there had been a geomagnetic reversal, there would have been an effect on 14C production; and subjunctive: whenever such an event occurred, as we know they did, then there would have been an effect. I think that with that in mind the tenses are OK in the rest of the paragraph, since "whenever" isn't counterfactual so I don't think I'm forced into the subjunctive, but let me know if you still see a problem. Re the last sentence; yes, I plan to put it into a footnote -- the kind in this section. Mike Christie (talk - contribs - library) 23:56, 27 July 2014 (UTC)

Thank you for your kind words. I'm glad I have been of help. I enjoy this kind of work, too. I understand what you are saying. I re-read the paragraph, and it makes sense (although I kind of wonder why geomagnetic reversal is even mentioned if it has had no effect on radiocarbon dating). In the following sentence:

"However, there are no well-established occurrences of either of these events in the recent enough past for there to have been an appreciable effect on present-day 14C measurements",

I don't understand the need for "present-day". Who else but humans in the 20th and 21st centuries would make radiocarbon dating measurements? CorinneSD (talk) 15:34, 28 July 2014 (UTC)

I made the changes outlined above. I agree with your comment about "present-day", but it's moot now as the phrase isn't in the new version of that paragraph.

I think I'm caught up. Do you have any more comments on the article? Mike Christie (talk - contribs - library) 01:08, 29 July 2014 (UTC)

I've made a few minor copy-edits. I hope you don't mind.

I need to go back to this revised section:

"Geomagnetic reversals, which change the polarity of the earth's magnetic field, would have had a significant impact on global ¹⁴
C production, since during these reversals the geomagnetic field becomes weaker, and stays weak for thousands of years during the transition. The field strengthens again as the reversal completes. Shorter-lived changes of polarity, known as polarity excursions, could in theory have affected ¹⁴
C production, but no global excursions are known to have occurred within the last 50,000 years".

I like the fact that you've made the paragraph shorter, but there is still something not quite right with the last sentence. I believe, -- unless there is something I'm not understanding -- either global geomagnetic reversals or polarity excursions "could in theory have affected 14C production", so tacking on "but no global excursions are known to have occurred within the last 50,000 years" to a sentence that is only about polarity excursions does not make sense. There is more than one way to fix this. I would like to suggest that you

• first explain what geomagnetic reversals are, and then mention the two or three types (I think Aitken mentions two types of global ones, but you could simplify to two -- global and polarity);

• then say that either type of activity could in theory affect 14C production; and finally

• say that no global or polarity excursions have occurred in the last 50,000 years.

If you cannot say with certainty that no polarity excursions have occurred in the last 50,000 years, then how can you be sure that there has been no effect on 14C production in the last 50,000 years?

If I'm not understanding something basic, I apologize. But I still think that last sentence is confusing. I also still think the jumping between tenses and moods in your verbs is confusing. CorinneSD (talk) 17:15, 29 July 2014 (UTC)

I've had another go at this, and I tried to fix the tense issue too. Here's the revised version:

There are two kinds of geophysical events which could have affected production in the past: geomagnetic reversals and polarity excursions. During a geomagnetic reversal the geomagnetic field becomes weaker, and stays weak for thousands of years during the transition to the opposite polarity. The field strengthens again as the reversal completes. A polarity excursion is a shorter-lived version of a geomagnetic reversal; polarity excursions can be either global or local. During a geomagnetic reversal or a global polarity excursion 14C production increases during the period when the geomagnetic field is weaker. In the last 50,000 years there have been no geomagnetic reversals, and no known global polarity excursions. (Local excursions would have had no significant effect on 14C production.)

Is that better?

To answer your other question, we can't be sure there's been no effect on 14C production, because there might have been a global polarity excursion that hasn't been detected yet. I think that's why Aitken mentions it; if it was certain this was all purely theoretical, it wouldn't be worth commenting on. Mike Christie (talk - contribs - library) 11:13, 30 July 2014 (UTC)

I think it is better. May I suggest an alternate wording? Everything except the last sentence is definition and explanation, all in present tense. The last sentence is specifically about the past.

There are two kinds of geophysical event which can affect 14C production: geomagnetic reversals and polarity excursions. In a geomagnetic reversal, the Earth's geomagnetic field weakens and stays weak for thousands of years during the transition to the opposite magnetic polarity and then regains strength as the reversal completes. A polarity excursion, which can be either global or local, is a shorter-lived version of a geomagnetic reversal and does not significantly affect 14C production. During either a geomagnetic reversal or a global polarity excursion, 14C production increases during the period when the geomagnetic field is weak. It is fairly certain, though, that in the last 50,000 years there have been no geomagnetic reversals or global polarity excursions.

CorinneSD (talk) 14:41, 30 July 2014 (UTC)

I like this version, but there's one inaccuracy: global polarity excursions could affect 14C production. A local excursion would not. Here's an attempt to fix that, based on your version:

There are two kinds of geophysical event which can affect 14C production: geomagnetic reversals and polarity excursions. In a geomagnetic reversal, the Earth's geomagnetic field weakens and stays weak for thousands of years during the transition to the opposite magnetic polarity and then regains strength as the reversal completes. A polarity excursion, which can be either global or local, is a shorter-lived version of a geomagnetic reversal. A local excursion does not significantly affect 14C production. During either a geomagnetic reversal or a global polarity excursion, 14C production increases during the period when the geomagnetic field is weak. It is fairly certain, though, that in the last 50,000 years there have been no geomagnetic reversals or global polarity excursions.

Does that work? Mike Christie (talk - contribs - library) 22:41, 30 July 2014 (UTC)

Oh. Sorry for that inaccuracy. Mike, this is really your article, so if you prefer your earlier version, above, I wouldn't mind at all. If you really do prefer the latest version, with your correction, that's fine, too. Your last version with the correction sounds fine. What would you think of changing

"A local excursion does not significantly affect 14C production" to

"A local excursion would not significantly affect 14C production"?

I have one more question. I might think an average reader upon reading this paragraph would ask, "If there have been no geomagnetic reversals or global polarity excursions in the last 50,000 years, why is this even being mentioned?" I think it is because it has to do with the measurements that have been taken, and calculations done, on data for the last 50,000 years, to come up with the calibration curves. Is this right? If I am right, I think an average reader might fail to make the connection. I'm wondering whether you think it would be a good idea to add one more sentence at the end of the paragraph to make the connection and explain the reason why all of this is important to know. Or do you think it is enough that it is in a series of sections, each having to do with things that scientists had to take into account when compiling the calibration curves? (I don't have the article open in a separate window; I'm going by memory here.) CorinneSD (talk) 00:39, 31 July 2014 (UTC)

I've made the change, including your suggested revision above. I'll think about the additional sentence you suggest, but at the moment I don't think it's necessary -- the context is a list of things that could have affected 14C production, so I think the reader will follow when reading the article linearly. Mike Christie (talk - contribs - library) 10:06, 1 August 2014 (UTC)

Comments

I went through the first 3 sections and tried to tighten the accuracy of the prose. I've added a couple of citation tags also. Two things that I've noticed:

• radiocarbon years: what is it concretely?

  The article currently gives a short definition the first time the term is used: '"radiocarbon years", meaning that the dates are calculated using Libby's half-life value and have not been calibrated'. A full definition would be quite long, so I didn't include it. Taylor (1987) p.4 defines a conventional radiocarbon age (which is the same thing) as including the following conventions: (i) the use of the Libby half-life in calculations; (ii) the use of the oxalic acid standard to define the zero ¹⁴
  C age of the terrestrial biosphere; (iii) the use of 1950 AD as the zero point when quoting the age in years; (iv) a fractionation correction; and (v) an assumption that ¹⁴
  C has been constant in all reservoirs over the ¹⁴
  C timescale. The two things in this definition which mean that the radiocarbon age is not the same as the calendar age are the use of the Libby half-life and the assumption that the ¹⁴
  C level has been constant over time. That's why I give the shorter definition in the article: calibrating corrects for both of those things, since a correction for the incorrect half-life is incorporated in the calibration curve. Hence I think the shorter definition is accurate as it stands. Mike Christie (talk - contribs - library) 10:37, 2 August 2014 (UTC)

If something is tedious to explain in the article, the you should still add it as a footnote. See List of gravitationally rounded objects of the Solar System. Nergaal (talk) 12:07, 7 August 2014 (UTC)

I think that's a good idea. Done; does that work? It refers to concepts not yet explained in the article; I tried to get around that with a couple of links. Mike Christie (talk - contribs - library) 22:22, 7 August 2014 (UTC)

• the article doesn't seem to explain concretely that after n*half-life, the concentration is 2^-n. This would not be obvious to a laymen. Please discuss this, and say that for example, after 57,500 years, the amount of C14 in the sample is a thousanth of the original sample. 12:43, 1 August 2014 (UTC)

  Done. The source includes a graph showing exponential decay; I didn't include a graph but let me know if you think one is necessary here. Mike Christie (talk - contribs - library) 10:37, 2 August 2014 (UTC)

• added more clarifyme tags

  I'm not clear on the issue with the two clarifyme tags. One is on this sentence: "The time it takes for carbon from the atmosphere to mix with the surface ocean is only a few years, but the surface waters also receive water from the deep ocean, which has over 90% of the carbon^{[clarification needed]} in the reservoir." The exact number (90.8%) is given in the diagram just to the right of that sentence. I'm not sure what's not clear here -- the deep ocean really does contain over 90% of the carbon in the reservoir, and the "carbon exchange reservoir" was defined higher up. The other tag is on "Using the calculation method given above to calculate the age of marine life^{[clarification needed]} typically gives an age of about 400 years." Here I think you mean that "the calculation method given above" isn't very specific, since the "Principles" section doesn't go into all the calculations. I've changed this and the preceding sentence to say "Creatures living at the ocean surface have the same 14C ratios as the water they live in, and as a result of the reduced 14C/12C ratio, the radiocarbon age of marine life is typically about 400 years." Mike Christie (talk - contribs - library) 11:05, 2 August 2014 (UTC)

  Just saw your note on the second one: "you mean a living fish is radiocarbon dated at 400 years old?" Yes, though that's radiocarbon years. I hope the revised wording makes that clearer. Mike Christie (talk - contribs - library) 12:08, 2 August 2014 (UTC)

• the svg image: add a 1.0 at the armosphere, remove citation and put it as a footnote in the caption

  Is that the standard way to do it? I added the citation information directly to the svg because I wanted it to be visible whenever anyone used the image. If that's not going to be the case, I think it might be better to remove it completely, and let the caption provide the citation. After all, putting a ^[1] there is going to conflict with the footnote numbering in the article. Mike Christie (talk - contribs - library) 11:17, 2 August 2014 (UTC)

I am pretty sure that including citations within the actual image is not the rule here. What you should do is to include in at File:Carbon_exchange_reservoir_2.svg#Summary. Nergaal (talk) 12:07, 7 August 2014 (UTC)

You're right, that's the best answer. Done. Mike Christie (talk - contribs - library) 22:49, 7 August 2014 (UTC)

How about replacing the dashes with parantheses and/or italics? Nergaal (talk) 12:11, 7 August 2014 (UTC)

Sorry, not sure which dashes you're referring to -- can you clarify? Mike Christie (talk - contribs - library) 22:49, 7 August 2014 (UTC)

• "but the same error term of 80 years could be obtained by doubling the counting time to 500 minutes" => something is missing here

  Can you tell me what you think is wrong here? I'm not seeing it. The error term was given as +/- 80 years, and the counting time as 250 minutes, in the previous sentence. What's missing? Mike Christie (talk - contribs - library) 11:18, 2 August 2014 (UTC)

It seems fine now but I had a hard time understanding it. I think in parts the text is a bit dense for non-experts. Nergaal (talk) 12:07, 7 August 2014 (UTC)

I tried to simplify this a bit. Mike Christie (talk - contribs - library) 22:35, 7 August 2014 (UTC)

• the article is bit too detailed IMO. I think "dating considerations" can be split into a separate article, and then trimmed to 2/3 or 1/2 of the current size. For example the C3 and C4 pathways while interesting, are they really necessary to the scope of this article?

  I've already cut quite a bit out of the article and moved it to sub-articles, and was hoping this was about the right length now. I went back and compared it to the longest FAs, and it wouldn't be the longest article, but it would be close. So I think you're right, more cutting is probably a good idea. I'll move the dating considerations section to a subarticle and post a note here when that's done. Mike Christie (talk - contribs - library) 11:46, 2 August 2014 (UTC)

  The point is not to have a long article, but an informative one to the average reader. I consider myself an above-average reader and I have a hard time finishing reading the entire article. Add more figures and tables to simplify the text. Nergaal (talk) 12:07, 7 August 2014 (UTC)

  OK, I've split that section to a sub-article, radiocarbon dating considerations. I cut the text in the main article by about 25% -- I removed some discussion of details, and a couple of discussions of points that are not thought to have much or any effect, like geomagnetic reversals and the island effect. Do you see anything else that is excessive detail for this article? Mike Christie (talk - contribs - library) 13:04, 2 August 2014 (UTC)

• "Isotope fractionation" a neat section, but only at the end I realized it is mostly about C13. Could you at least remind at the end of the section that all this is for C13, and for C14 the effect is larger? Also usually by what factor larger? Otherwise it seems to be a bit out of context. Also, trim many of those values, and perhaps put them into a table.

  Good point about the 13C/12C ratio seeming to be off-topic. I've added a note at the start, rather than the end, since that will let the reader know why the discussion is about 13C. The article does say the fractionation for 14C is twice that of 13C -- it's the last sentence of the second-to-last paragraph of that section. I'd rather not cut the values and put them in a table -- the text currently explains the reasons for the different values for marine organisms inline, and I think that's better for the reader than having to go back and forth from the table to the text to understand. I think a table could be added, without cutting the values, but with the image there I was afraid it would look a bit cluttered (and I really like that image and would rather not lose it). Mike Christie (talk - contribs - library) 11:34, 2 August 2014 (UTC)

What is PDB? "ratio can be easily derived from it" how? Add a footnote. Yes the text explains it but IMO it only makes the article look intimidating. You could have a table, and either add footnotes, or explain only some of the entries from the table in the text. How would the Carbon exchange reservoir section be without the svg? Much more difficult to quickly understand. Nergaal (talk) 12:07, 7 August 2014 (UTC)

Footnote added, and clarification of the relationship between delta 13C and delta 14C. I also added a small table. Mike Christie (talk - contribs - library) 02:43, 9 August 2014 (UTC)

• how about impact onto other dating techniques? I think some isotopes or zirconium and uranium are used in geology.

  There are several other radiometric dating methods, involving argon, potassium, uranium, and some less common methods. I didn't really see a good place to mention these (and the article is already long). However, a previous editor added the Chronology template at the bottom of the article, which includes some of these links. Is that enough? Mike Christie (talk - contribs - library) 11:34, 2 August 2014 (UTC)

  Follow-up: I have now added a paragraph on other dating methods at the end of the article. Mike Christie (talk - contribs - library) 11:22, 9 August 2014 (UTC)

A really nice and impressive article overall, but there is so much info that at some point I found it hard to continue reading it. Nergaal (talk)

A couple more points: you added a fact tag to "If it is assumed that the cosmic ray flux has been constant over the last ~100,000 years". That discussion is really about radiocarbon ages, so it's listing the assumptions that are made in calculating radiocarbon years. There's no assertion there that the flux really has been constant; it's just an if-then statement. However, Bowman does explicitly list constant 14C production in her coverage of this, so I added a citation anyway.

I tweaked a couple of your copyedits a bit; take a look and see if everything still looks OK. I also removed one citation needed tag (on the fact that 14C is known as "radiocarbon") because it was already cited; the whole paragraph is covered by the citation at the end of the paragraph.

Finally, thanks for the review! Mike Christie (talk - contribs - library) 12:08, 2 August 2014 (UTC)

I sometimes prefer repeating a citation when there is a strong statement made early in the paragraph. At least that way it is clear that the statement is from an actual referenced article. Nergaal (talk) 12:07, 7 August 2014 (UTC)

I do the same, e.g. for quotes, but I don't think it's necessary in this case. Mike Christie (talk - contribs - library) 01:25, 10 August 2014 (UTC)

• "value of -25‰" uses dash Nergaal (talk) 12:07, 7 August 2014 (UTC)

  Fixed in a couple of places. Mike Christie (talk - contribs - library) 11:23, 9 August 2014 (UTC)

• 11 sections is a bit much. It gives the impression of lack of structure. Consider checking DNA nanotechnology, Oxidative phosphorylation, Atomic line filter, Distributed element filter, and Gas tungsten arc welding for having a more clear structure. Nergaal (talk) 12:20, 7 August 2014 (UTC)

Just to clarify, what I mean is merge sections as subsections within broader sections. Nergaal (talk) 11:39, 9 August 2014 (UTC)

Done. I'm not entirely happy about "Origin" as the title for the new first section -- perhaps "Origin of the method"? Mike Christie (talk - contribs - library) 01:35, 10 August 2014 (UTC)

• beta counting and AMS are not wikilinked. Nergaal (talk) 11:35, 9 August 2014 (UTC)

  AMS is wikilinked on its first appearance as "accelerator mass spectrometry", and AMS is explained on first use. "Beta counting" isn't linked; I'm not sure where it would link to. What did you have in mind? Mike Christie (talk - contribs - library) 01:35, 10 August 2014 (UTC)

@Nergaal: I think I've caught up with your comments now. Mike Christie (talk - contribs - library) 01:35, 10 August 2014 (UTC)

Additional comment from Aa77zz

Thermoluminescence dating can be used to date ceramic objects that are a few thousand years old and thus within the time scale of C14 dating. The technique is listed in the collapsible Chronology template at the bottom of the article, and is mentioned (without a link) in the "Reporting dates" section, but it may be worth adding a sentence to the article. Aa77zz (talk) 09:56, 3 August 2014 (UTC)

Since Nergaal, above, suggested something similar, I went ahead and added a paragraph at the end of the impact section listing various categories of dating method, including thermoluminescence. Mike Christie (talk - contribs - library) 12:03, 3 August 2014 (UTC)