Wikipedia:Featured article candidates/Radiocarbon dating/archive1

The following is an archived discussion of a featured article nomination. Please do not modify it. Subsequent comments should be made on the article's talk page or in Wikipedia talk:Featured article candidates. No further edits should be made to this page.

The article was promoted by Ian Rose via FACBot (talk) 05:42, 12 April 2015 (UTC) [1].

---

Radiocarbon dating

Nominator(s): Mike Christie (talk - contribs - library) 17:26, 6 March 2015 (UTC)

Radiocarbon dating has revolutionized archaeology, and the invention of the method earned Willard F. Libby a Nobel Prize. I've been working on the article for over a year, and I think it's now ready to be nominated here. It's benefitted from a peer review, where several editors helped improve the article; I would particularly like to thank Aa77zz and CorinneSD. Since then it's been copyedited by Eric Corbett. Three professional archaeologists have looked over the article, including one who specializes in the topic, and their comments have been addressed. The article is a departure from my previous nominations, which have all been in the humanities; I would like to make it clear that I have no special expertise in this area and wrote it as a layman. I hope you find the topic as interesting as I do. Mike Christie (talk - contribs - library) 17:26, 6 March 2015 (UTC)

Support As Mike mentions above, I took part in the peer review. This is an important article and Mike has done a fine job in bringing it up to the FA standard. Aa77zz (talk) 20:36, 6 March 2015 (UTC)

Image review

• File:Willard_Libby.jpg: suggest including the {{non-free biog-pic}} tag. Nikkimaria (talk) 04:09, 7 March 2015 (UTC)

Done. Thanks for the review. Mike Christie (talk - contribs - library) 11:26, 7 March 2015 (UTC)

• Comment: The licensing for the lead picture is a little all over the place. Basically, we need to work out whether, as far as the English Wikipedia is concerned, the image is PD or non-free. If it's PD, it's going to need a careful explanation of the fact (along with the removal of the non-free tags); if it's non-free, its use in this article fairly clearly fails NFCC#8. Josh Milburn (talk) 23:09, 7 March 2015 (UTC)

  I'm not expert on images, but I've removed it on based on your comment and this conversation on commons. It seems that nobody has been able to show they're PD in the US. I just looked at the NFCC conditions and I agree it fails 8. Mike Christie (talk - contribs - library) 12:06, 8 March 2015 (UTC)

• Comment Sorry I missed the peer review. On a quick look, I think the article gets too scientific too quickly, and some of the sections at the bottom should precede the formulae etc, which will just lose a high % of readers, In particular, the explanation of how radiocarbon dates should be reported should be much higher up, before all the various factors are gone into. People who won't want to read about the physics want to know what the complicated notation of reported dates means. The full length of the lead is not used, and there maybe a case for a summary section after that. A clear statement of the current understanding and practice early on would be good. At the moment much of the article recapitulates the theory as it has developed. It's a bit late now I realize, sorry. Johnbod (talk) 15:35, 8 March 2015 (UTC)

  I'm open to changing the organization, and even withdrawing the FAC if necessary, to get it right, but for a big change like this I'd like to see consensus that it's necessary, and with two supports, and Eric's comment below, I'd be hesitant to act on your comment just yet. Though it's probably worth noting that both Eric and AA77zz have technical backgrounds (or so I understand). Perhaps other editors with a humanities background will weigh in. Re the lead: anything in particular you feel is missing? Mike Christie (talk - contribs - library) 18:18, 8 March 2015 (UTC)

I just saw that one of the paras was pretty short. I don't think all the article sections are summarized yet. I also notice that it is not clearly stated at the start that it can only be used for organic materials - easy to fix. Johnbod (talk) 19:29, 8 March 2015 (UTC)

I added a sentence about sample form to the shortest lead paragraph. I thought about mentioning the fact that there are separate marine and southern hemisphere calibration curves, but it's hard to do that without any explanation. I think every section is at least represented in the lead. Mike Christie (talk - contribs - library) 20:09, 8 March 2015 (UTC)

I also added a sentence to the lead explaining the BP notation, and mentioned that the objects to be dated have to be organic. Mike Christie (talk - contribs - library) 11:10, 9 March 2015 (UTC)

• Support. I don't agree with Johnbod's comments above, the structure of the article seems just fine to me. Eric Corbett 15:57, 8 March 2015 (UTC)

• Overall this is a remarkably readable discussion of a fairly technical topic. Nice job! I made a small number of text edits. I have a few picky comments/questions:

• In the Principles section, last paragraph: you say these "have not been calibrated", but presumably that just means using Libby's value for the half-life and doesn't refer to the calibrations for variations in historical 14C/12C ratio discussed below?

  It does mean that it has not been calibrated using the historical variation in ratio. Note 2 is intended to clarify this - part (e) is equivalent to saying that there is no calibration. I put it in a note because the definition is a little long to be placed parenthetically, but perhaps I should move it up to a box? As I understand it, the reason to include fractionation in radiocarbon years but not calibration is that calibration curves can vary, and if you want to apply a different calibration curve (e.g. a later INTCAL curve) to data in a paper you're reading, you want the uncalibrated age to apply the curve to. Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

  Sorry, I missed note 2 entirely. Readers who are interested in the details are probably more observant than me, though! Opabinia regalis (talk) 06:10, 14 March 2015 (UTC)

• If the PDB standard has an anomalous carbon ratio, how/why did it become the standard of comparison?

  I haven't seen this covered anywhere. I imagine it could be found by chasing a trail of paper references, but Taylor and Bar-Yosef, which is by far the most detailed history, don't even provide a cite for it. I've done some searching (I have JSTOR access) but couldn't find anything. Is this needed for the article? Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

  No, just curious if there was a story behind it :) Opabinia regalis (talk) 06:10, 14 March 2015 (UTC)

  I found this which indicates that Urey developed the PDB standard as part of his palaeotemperature work on oxygen isotope ratios. Presumably the PDB standard was then adopted for radiocarbon dating because the isotope ratios of the formation were well known. Mike Christie (talk - contribs - library) 20:10, 25 March 2015 (UTC)

• You mention the apparent ~400yr age for marine life twice and give an average of 440yrs once, with different citations each time.

  I changed these all to 440, which is much the most recent source, on the assumption that that would be the most accurate. Mike Christie (talk - contribs - library) 02:11, 14 March 2015 (UTC)

• "The deepest parts of the ocean mix very slowly with the surface waters, and the mixing is known to be uneven." - I'm usually against the "I never go outside, so I challenge your claim that the sky is blue" types of arguments, but when you use the phrase "known to be" that seems to merit a cite at the end of the sentence (or just delete the phrase).

  I deleted "known to be"; the source definitely supports uneven mixing, so I think that fixes it. Mike Christie (talk - contribs - library) 02:26, 14 March 2015 (UTC)

• In measuring the freshwater effect, you write that one usually just measures a modern sample. Does that mean changes in groundwater flow patterns that vary exposure to old-carbon rocks are rare enough to be negligible?

  That's certainly the implication. I looked at a more recent source and was able to find a discussion of this; it's apparent that testing a modern sample is not best practice, so I changed this. Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

• Hydroxyproline was thought to a reliable indicator of what? I don't quite follow this - it's a major constituent of collagen, but if you have a sample that you know contains collagen, what do you need hydroxyproline to indicate? Is this referring to identifying a sample as collagen-containing in the first place?

  There are problems with dating degraded collagen because it's possible that it could have been contaminated by more recent organic material. One way to confirm that the material you're looking at is original is to verify that the ratios of amino acids are correct; that tells you that you're looking at a sample that is essentially the same composition as the original bone. If hydroxyproline is only found in bone, then separating it and testing only that would be safe because it would eliminate contaminants. I'm thinking that perhaps this should just be cut; since it's been found in groundwater it's no longer that important, and it may be too detailed an issue for this article, which is a summary. Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

  Ah, I see, the modern contaminant is presumably not collagen. "A reliable indicator of purity" or "indicating the absence of modern contamination" or similar would make this clearer, though if it's not a current technique removing it is probably better. (I would not have guessed you'd find hydroxyproline in groundwater, but following the links suggests the type deposited in silica is chemically distinct from the hydroxyproline in animal collagen; this is totally off-topic, but I wonder if they can be distinguished to avoid this problem?) Opabinia regalis (talk) 06:10, 14 March 2015 (UTC)

  I mentioned this to my archaeologist brother-in-law and he wasn't aware of work along those lines. Might be a research project for someone .... Mike Christie (talk - contribs - library) 20:10, 25 March 2015 (UTC)

• HOxII is oxalic acid, right? Any reason not to wikilink this?

  I didn't because it's really the name for the standard, and I thought it might be slightly misleading. I could avoid this by slightly expanding the sentence if you think it's worth it -- e.g. "The most common standard sample material is oxalic acid, such as the HOxII standard..." if you think it's worth it. Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

  IMO the expanded version would be useful. I didn't know what it was, so I googled it and found all kinds of stuff about a particular hox gene.

  That did make me think of another question, though - why oxalic acid as a standard when the test materials are converted to benzene, graphite, etc? Opabinia regalis (talk) 06:10, 14 March 2015 (UTC)

  I can't find out why oxalic acid was chosen. Taylor and Bar-Yosef say that the original standard was prepared in 1956 at the request of James Arnold, so it was specifically for radiocarbon. I did find this discussion, which mentions that oxalic acid has some disadvantages. I can't find any publications from the NIST (or NBS as it was then) that explain it. Mike Christie (talk - contribs - library) 20:10, 25 March 2015 (UTC)

  @Opabinia regalis: FYI, I contacted R.E. Taylor, one of the authors of the most recent specialist book on the history of radiocarbon dating, and he said that he believed it was because there's a high oxalic acid content in beet leaves compared to other plants, and Arnold knew the year of growth of the batch of beets that would be tested. Taylor also said he understood the extraction of oxalic acid is straightforward, though he also has heard that the extraction had to be redone because of some errors. Anyway, he's planning to check on these questions the next time he's at UC San Diego and can look at James Arnold's papers. That won't give me a source, of course, but if he puts it in a note I can use that. Mike Christie (talk - contribs - library) 15:37, 29 March 2015 (UTC)

  Interesting! I guess they had decided on oxalic acid and then went with beets instead of having a convenient pile of beets and going with the easiest chemical. You are going way above and beyond on the investigations here :) Opabinia regalis (talk) 04:25, 30 March 2015 (UTC)

• "one archaeologist" - any reason not to name this person? This reads strangely with Taylor prominently mentioned in the same paragraph and quoted in the one before.

  Agreed; I've added his name. Mike Christie (talk - contribs - library) 02:20, 14 March 2015 (UTC)

• On the structure question mentioned above: I think the current order of presentation works well, especially since the TOC headings are clear and can direct the reader past the details if they don't want to read everything. My only (subjective, not really actionable) comment here is that the article seems to end abruptly. The last two paragraphs of the Impact section don't seem to connect well to the preceding discussion. I think an example or two of real archaeological data - not pop fluff like the Shroud of Turin - would help bring things together. Maybe the last paragraph could be split into its own subsection.
• The article is unusually image-depleted, especially with the loss of the Libby portrait. Any thoughts on a replacement lead image? Opabinia regalis (talk) 07:15, 12 March 2015 (UTC)

Thanks for the review; I should have time this evening to work on these points. One quick note about images: I haven't come up with anything for a lead image; I would love to get a free picture of Libby for the lead, but can't find one. It's not a subject that lends itself well to photographic illustration. If I add a discussion of an archaeological use of radiocarbon dating, as you suggest (and I agree that's a good idea) then perhaps a picture of the dig or location would work. Mike Christie (talk - contribs - library) 12:24, 12 March 2015 (UTC)

I've added a few comments above but am out of time this morning. I should have a little more time tonight and will do more. I'm away from my sources for a week starting tomorrow, and will probably have very limited access to the internet, so I may not be able to do much more until about 3/22. Mike Christie (talk - contribs - library) 11:56, 13 March 2015 (UTC)

@Opabinia regalis: I've responded to all but your final point, and in regards to that I think it would be worth giving a more detailed example of a significant real use of the technique in archaeology. Taylor & Bar-Yosef give lots of examples and I'll pick something they highlight. However, I won't be able to do much on this for a week as I'll be skiing in Colorado. I'll have an iPad, but limited internet and none of my references. More when I return. Mike Christie (talk - contribs - library) 02:26, 14 March 2015 (UTC)

Thanks, looks good - I'll support with an example. No ipads on vacation! :) Opabinia regalis (talk) 06:10, 14 March 2015 (UTC)

No iPad? You've been talking to my wife. :o) I had time this morning to add one notable application, and I'll do at least one more when I get back. Mike Christie (talk - contribs - library) 12:09, 14 March 2015 (UTC)

I got packed early and have snuck in one more under the wire. Let me know what you think. Mike Christie (talk - contribs - library) 13:43, 14 March 2015 (UTC)

Very interesting examples! A question on the first one: I read skimmed both Pleistocene and Holocene and I'm still unclear as to how the boundary was defined in the first place, other than that ice locations are involved - which makes the matter of identifying the date somewhat opaque. Is this possible to clarify briefly?

I don't know about briefly! Here's the explanation -- tell me if this is something you'd like to see in the article. The boundary is defined by tracking the δ¹⁸O ratio; that is, the ratio of ¹⁶
O to ¹⁸
O. Higher temperatures put more ¹⁸
O in the atmosphere (from evaporation) and so precipitation in warmer times has higher δ¹⁸O. Ice cores from Greenland can be used like tree rings to produce a graph of δ¹⁸O over time. If you look at page 4 of this book you'll see a graph showing an unmistakable sharp change in climate at 11,650 ± 99 cal BP. That's the Pleistocene-Holocene boundary. Mike Christie (talk - contribs - library) 20:21, 25 March 2015 (UTC)

Hmm, that is a lot of info - is it too oversimplified to just say this boundary marks a dramatic change in climate and leave it at that? Opabinia regalis (talk) 05:54, 26 March 2015 (UTC)

I went with "Establishing the date of this boundary − which is defined by sharp climatic warming − as accurately as possible has been a goal of geologists for much of the 20th century." Mike Christie (talk - contribs - library) 21:00, 26 March 2015 (UTC)

And a question on the second one: the Dead Sea Scrolls article says they're the second-oldest Bible manuscripts, but also has sections tagged as outdated. Is there a subset of the Dead Sea Scrolls that have previous versions, or is the other article wrong? I'd be tempted to trim the last couple of sentences of the dead sea scrolls paragraph ("some scholars" vs "most scholars" etc...) - it sounds like there's more controversy than can be stuffed into a couple of sentences without losing detail.

I cut the last sentence. That part of the controversy is essentially theological, or at least ideological, and is not really a scientific debate; I put it in as an indication that these measurements don't always settle the issues in everyone's eyes, but I don't think that's really necessary. People can follow the links (or go read the Shroud of Turin article) if they want more details. Mike Christie (talk - contribs - library) 20:52, 25 March 2015 (UTC)

This could go either way but I think the examples would fit more naturally after the general "impact" section, with maybe the last paragraph split off into a separate section ("other dating methods" or similar?). Not a strong preference though. Have a good vacation! Opabinia regalis (talk) 06:53, 15 March 2015 (UTC)

I'd like to leave the examples where they are, unless you feel strongly about this. I think one benefit of the examples is that they set up the reader for a better understanding of how dramatic an impact radiocarbon dating can have on an archaeological debate, so having the impact section follow the examples seems right to me. @Opabinia regalis: I think I've now replied to all your comments. Mike Christie (talk - contribs - library) 20:52, 25 March 2015 (UTC)

Thanks for the ping, read it over again and support, nice work! Opabinia regalis (talk) 05:54, 26 March 2015 (UTC)

Comments

• I am more familiar with the term carbon-14 dating, which is the title of the Britannica article ("Carbon-14 dating, also called radiocarbon dating"). I would suggest adding this alternative name.

  Agreed; done. Both are already redirects. Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

• I think the half-life is so crucial that a sentence about it ought to be in the lead.

  Done, in the context of the maximum datable age. Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

• In the main text you explain half-life twice. I would merge them.

  I eliminated the second explanation; does that do it? Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

• "For more than a decade after Libby's initial work, the accepted value of the half-life for 14 C was 5,568 years; this was improved in the early 1960s to 5,730 years." I think revised (or corrected) would be a better word than improved.

  I went with "revised". Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

• "It is possible to incorporate a correction for the half-life value into the calibration curve, and so it has become standard practice to quote measured radiocarbon dates in "radiocarbon years", meaning that the dates are calculated using Libby's half-life value and have not been calibrated." I had to read this several times but I think I now understand it. So "radiocarbon years" does not correct for different levels of C14 in the atmosphere at different periods and also adopts the wrong figure for the half-life which was current in the 1950s? Would not the statement that the use of radiocarbon years is standard only apply in technical papers on C14 dating? The only time I remember coming across it was in a case I recently raised with you. BTW I once complained to an expert that I find the mixture of calibrated and uncalibrated years in the Wiki articles on the Dryas ice ages confusing, and he replied that it is worse than that as in some papers it is not clear whether they are giving calibrated or uncalibrated figures.

  Yes, you have it exactly right. I'm not entirely sure I know what you mean by "technical papers on C14 dating" -- do you mean any scholarly paper that mentions radiocarbon dates, or specifically papers about the mechanics of dating? The former is true, as far as I can see -- the journal Radiocarbon's recommendations are intended to apply to any paper that reports radiocarbon dates. Not that eveyone follows the recommendations, as your friend pointed out. The reason the recommendation is always to give uncalibrated (i.e. radiocarbon) dates is that a reader can then apply a different (e.g. later and presumably more accurate) calibration curve and derive a calendar date from an old paper. Does that answer your question? Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

  There are two points here. 1. As I said, I had to read the sentence several times before I was clear what it meant. I think it could be more clearly expressed. 2. When I referred to "technical papers" I meant that only experts understand "radiocarbon dates" and would be able to adjust them according to their own views. The vast majority of people would take the term to mean a true date determined by C14 dating. For example, Pettit and White's The British Palaeolithic is a summary of the state of knowledge for professionals in the field, but it uses calibrated dates throughout - as it is directed at archaeologists, many of whom would presumably not understand radiocarbon dates and take them as true dates BP. Your statement that the recommendation is to always use radiocarbon dates can only apply to papers directed to experts who understand them, not to the wider community of archaeologists who use them in their work without understanding the technicalities, let alone the wider interested public. Dudley Miles (talk) 23:08, 25 March 2015 (UTC)

  To your first point, how about " It is possible to incorporate a correction for the half-life value into the calibration curve, and so measured radiocarbon dates can be quoted in "radiocarbon years", meaning that the dates are calculated using Libby's half-life value and have not been calibrated. As a result, when a date is quoted, the reader should be aware that if it is an uncalibrated date it may differ substantially from the best estimate of teh actual calendar date." The second sentence, I hope, clarifies things; I also changed "standard practice" to "can be quoted" to address the fact that Radiocarbon's recommendations are not universally followed. Re point 2: Pettit & White say on page 9 "Reimer et al. suggest that where calibrated dates are used original radiocarbon measurements on which they are based should also be cited. We do this where we think it is necessary, but in the interests of space do not make a habit of it. We cite references to the publications in which the original radiocarbon measurements were presented and thus, where we do not present original measurements in tables or text, readers, should they wish, may follow a trail back to original sources and check the accuracy of our calibration". I think this can be taken to indicate that you're right that it's at the discretion of the author. Spot checking elsewhere suggests to me that articles that give original research on dating or which provide the first dates for samples are more likely to give uncalibrated dates, but where the author is using someone else's data he only gives the uncalibrated date when there's a reason to do so. Does the change I propose above address your concerns? Mike Christie (talk - contribs - library) 00:10, 26 March 2015 (UTC)

  "It is possible to incorporate a correction for the half-life value into the calibration curve, and so measured radiocarbon dates can be quoted in "radiocarbon years", meaning that the dates are calculated using Libby's half-life value and have not been calibrated." I still find this puzzling. I am not sure you ever fully explain "calibration curve", but I take it that it is a line on a graph of years against C14 values derived from a sample of known age - eg from tree rings. "a correction for the half-life value" presumably means adjusting the date to agree with the wrong 1950s half-life, but it seems an odd way of putting it. How about something like "Dates can be given which are calculated using Libby's incorrect 1950s value for the half-life of C14, and also without calibrating for changes in the proportion of C14 in the atmosphere at different periods. This allows experts to apply their own views about the correct values for calibrating C14 dates. These are called "radiocarbon dates" or "uncalibrated dates", whereas true calendar dates are "calibrated dates"." BTW you seem to have forgotten to change "standard practice" to "can be quoted".

  I hadn't made the full edit I thought I did; sorry. I've done so now. I'll think some more about your suggested wording; I don't like "true" as an adjective, but I see what you're getting at. Does the calibration section of the article give sufficient detail? I deferred the explanation of the curves to that section, thinking it would be too complicated at this point in the article. Mike Christie (talk - contribs - library) 01:23, 27 March 2015 (UTC)

  I still find this sentence confusing, although I agree that your "best estimate of the actual calendar date" is better than my wording (which in any case you can no doubt improve). Also it is not clear when you refer to radiocarbon years and uncalibrated dates that they are synomyms. (I assume they are - until I read this article I assumed that uncalibrated just meant not calibrated for changes in C14 levels, not a wrong figure for the half-life.) Note 2 is against the best estimate of the actual date, and so it is not clear what "also" refers to. A further point is that I think that as a general principle an article should always explain a technical term like calibration curve the first time it is used, as otherwise the reader cannot be expected to know what you mean. Basically I think that you are explaining a key point here which needs to be explained in simple language for the non-expert. Dudley Miles (talk) 19:33, 29 March 2015 (UTC)

  I agree this needs to be clear, and I'm happy to keep working on it; I can see it's a confusing point. I've expanded the discussion; let me know what you think. If this is not enough, then perhaps it would be best to just cut the whole paragraph -- which I think I originally intended to be an aside to the reader, to let them know complications were coming -- and defer the discussion of radiocarbon ages to the calibration section instead. That way the information comes at a point where it is natural to explain it a little more slowly. Mike Christie (talk - contribs - library) 21:36, 29 March 2015 (UTC)

  This seems much clearer, except that it is still not spelled out whether radiocarbon years and uncalibrated dates mean the same thing. I think you need to explain terms when they are first used, so you cannot cut the whole paragraph unless you avoid referring to radiocarbon years and calibration curves until they are explained. Dudley Miles (talk) 22:48, 31 March 2015 (UTC)

  I've added a parenthesis that I hope resolves this. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• "sea organisms have a mass of less than 1% of those on land" - no change needed but I find this amazing.

  Me too. I checked the source (it's viewable in Google Books if you're curious) and confirmed it; it shows marine biota at 3 billion tonnes of carbon, and land vegetation at 615 billion tonnes. I guess there are large areas of the deep sea that are effectively deserts, whereas most of the land has vegetation of some kind or another. And sea vegetation never reaches the mass that trees do. Mike Christie (talk - contribs - library) 21:37, 25 March 2015 (UTC)

  I did a double-take at this too. But whales! But... oh, trees. Opabinia regalis (talk) 05:54, 26 March 2015 (UTC)

• "To verify the accuracy of the method, several artefacts that were datable by other techniques were tested; the results of the testing were in reasonable agreement with the true ages of the objects. In 1958, Hessel de Vries was able to demonstrate that the 14 C/12 C ratio had changed over time" This is unclear. Did early tests suggest that C14 does not vary, which were disproved by de Vries? If so this should be clarified. (I once read that doubts were first raised due to discrepancies between the known dates of ancient Egyptian artefacts and C14 dates, but maybe this is a myth.)

  This got me digging and I discovered that the sentences you quote include some material that predates my involvement with the article. I was evidently not very careful when I switched citations; the citations I give support a date in the 1960s, not 1958. The 1958 date comes from "Münnich KO, Östlund HG, de Vries H (1958). "Carbon-14 Activity during the past 5,000 Years". Nature 182 (4647): 1432–3. Bibcode:1958Natur.182.1432M. doi:10.1038/1821432a0" which I haven't seen and don't have access to. I'll see if I can get hold of a copy and get back to you on this. However, to answer your question, the initial investigations did not use objects of precisely known age, and since the error bars were fairly broad on the early dates, it wasn't clear there was a problem. De Vries and others worked on getting ¹⁴
  C dates from tree rings since it was clear that would validate the results; and in addition, as you say, discrepancies were becoming apparent with Egyptian chronologies. Assuming that the Nature article cited supports what's stated in the article, I'll add it as a citation, and then for clarification how about this: "To verify the accuracy of the method, several artefacts that were datable by other techniques were tested; the results of the testing were in reasonable agreement with the true ages of the objects. Over time, however, discrepancies began to appear between the known chronology for the oldest Egyptian dynasties and the radiocarbon dates of Egyptian artefacts. Neither the pre-existing Egyptian chronology nor the new radiocarbon dating method could be assumed to be accurate, but a third possibility was that the ¹⁴
  C/¹²
  C ratio had changed over time, and this was demonstrated in 1958 by Hessel de Vries." Though I'm not sure why later sources only talk about de Vries and don't mention his co-authors. Anyway, I'll get back to you on this. Mike Christie (talk - contribs - library) 01:25, 26 March 2015 (UTC)

  I have now seen the Nature article and it definitely does not support de Vries as the person who verified that the ratio had varied historically, so I've modified that section to go with the other sources I have. Mike Christie (talk - contribs - library) 20:57, 26 March 2015 (UTC)

• So tree rings provide a check on the level of atmospheric carbon back c 14,000 years. How do they check it in earlier periods? Ice cores?

  The INTCAL13 article lists plant macrofossils, speleothems, corals, and foraminifera as data sources, in addition to tree rings. I could add something to this but I was thinking this sort of detail would go better in the subarticle on calibration. Mike Christie (talk - contribs - library) 01:36, 26 March 2015 (UTC)

  I think it is worth a sentence.

  Done; added in the calibration section, where the discussion of the INTCAL13 curve is. Mike Christie (talk - contribs - library) 01:23, 27 March 2015 (UTC)

• Why mention the C3 and C4 pathways when you do not say there is any difference in their C14 uptake.

  C4 plants have higher (less negative) δ¹³C values. I think the details were originally in the article and were moved to the subarticle on dating considerations. Do you think I should remove the reference to C3 and C4 completely, or mention that there's a difference? Mike Christie (talk - contribs - library) 01:36, 26 March 2015 (UTC)

  It depends how significant you think it is. I think you need to go into more detail or delete.

  I deleted it; I think it would take longer to explain than is appropriate for this level of detail. Mike Christie (talk - contribs - library) 01:23, 27 March 2015 (UTC)

• Apologies if I am showing my ignorance, but in the Isotopic fractionation equation, does not multiplied by 1000 parts per thousand mean multiplied by 1?

  I assume you mean the $\times 1000\ ^{o}\!/\!_{oo}$ in the equation? It was meant to indicate "multiply by 1,000" with the ‰ sign giving the unit notation. Or are you referring to something else? Mike Christie (talk - contribs - library) 01:36, 26 March 2015 (UTC)

  I think I see now. I was thinking 5x100%=5, so why does not 5x1000 parts per thousand=5, but you mean times 1000 with the answer in parts per thousand.

  Yes, that's the intent. Mike Christie (talk - contribs - library) 01:23, 27 March 2015 (UTC)

• More to follow. Dudley Miles (talk) 21:57, 16 March 2015 (UTC)

  Sorry I've been so slow to respond; I was on vacation for a week and have had a filthy cold since I got back. I hope to get back to Aethelwulf shortly too. Mike Christie (talk - contribs - library) 01:36, 26 March 2015 (UTC)

  @Dudley Miles: I've now responded to everything above. Mike Christie (talk - contribs - library) 20:57, 26 March 2015 (UTC)

  I am away for the weekend and will look at the rest of the article next week. Dudley Miles (talk) 22:58, 26 March 2015 (UTC)

• Some further comments above - others below on the rest of the article.
• What is the fossil-fuel effect?

  It's defined in the atmospheric variation section; it refers to the effect of burning fossil fuel over the last 120 or so years; a lot of old carbon has been released into the atmosphere, lowering the ¹⁴
  C/¹²
  C ratio. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

  Ah. I see I Ctrl-F does not find it because you spelled it without the hyphen before. Dudley Miles (talk) 10:34, 3 April 2015 (UTC)

  Good catch. I took out the hyphen; the sources vary on this so I went with the most recent source. Mike Christie (talk - contribs - library) 17:42, 4 April 2015 (UTC)

• "In 1970, the British Museum radiocarbon laboratory ran weekly measurements on the same sample for six months. The results varied widely (though consistently with a normal distribution of errors in the measurements), and included multiple date ranges (of 1σ confidence) that did not overlap with each other. The extreme measurements included one with a maximum age of under 4,400 years, and another with a minimum age of more than 4,500 years." Have not methods improved so much over that 45 years since then that this is no longer relevant?

  The point is not that their measurements were accurate: the reverse is true, in fact -- the experiment is a demonstration that ordinary statistical variation will often given you results outside the 1σ confidence range. It's intended to make it clear that a 1σ range of e.g. 11,300 to 11,000 BP doesn't mean the date was definitely in that range. I've rephrased to try to make this clearer. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• "published in 1998, and updated in 2004, 2009, and, most recently, 2013" - recentism!

  I cut "and most recently"; it's (currently) true, but unnecessary, and I think an "as of" phrasing would be ugly. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• The source for dendro dates going back 13,900 years says that this applies to the northern hemisphere. Do you know how far they go back in the southern one, and whether southern C14 dates are less accurate as there are not so many sources of absolute dates for comparison?

  I don't, and I'd have to dig into the papers to find this out. The 1σ errors on the INTCAL curves give a feel for the accuracy of the curve; if I wanted to compare the accuracy of the curves I would probably look at the difference between the size of the error bars at various dates. Do you feel a note on this is necessary for this article? If I had the data I'd probably put it in the calibration subarticle rather than this one. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

  Are C14 dates for the southern hemisphere less accurate? If so I think it is worth mentioning it. Dudley Miles (talk) 10:34, 3 April 2015 (UTC)

  It appears they are not significantly less accurate. I was able to find a recent (2014) paper that says "Although the 14C calibration curves from the Northern Hemisphere (NH) and SH are broadly similar, there are subtle differences between the structural forms of each curve"; I don't think it's worth adding a comment on this since it would say little more than "the curves are not identical", which is already apparent from the fact that there are two curves. Mike Christie (talk - contribs - library) 17:42, 4 April 2015 (UTC)

• Are there cases where wiggles in the curve mean that a particular C14 ratio can mean two alternative calibrated dates? (I see in the Dead Sea Scrolls discussion that there are. It might be worth covering this.)

  Yes, definitely. Take a look at calibration of radiocarbon dates; I put together a detailed example with several graphs but moved it to this subarticle as being too complicated for the parent article. I can't see easily explaining this without moving quite a bit of this material back. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

  I think this is an important point which needs be in there, and you do briefly explain it in the Dead Sea Scrolls section. I would move that explanation to the relevant place above, rather than mention it in passing here. Dudley Miles (talk) 10:34, 3 April 2015 (UTC)

  Thinking about it I agree, particularly since it comes up in the Dead Sea Scrolls discussion. I added a couple of sentences; does that do it? Mike Christie (talk - contribs - library) 17:59, 4 April 2015 (UTC)

• "In 2014, Higham and co-workers" I would give his first name, Tom.

  Done. I wonder if it would be better to switch to passive and leave out the name of the author. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• "the bitumen's radiocarbon age will be greater than is measurable by the laboratory" I do not understand this. As bitumen is a form of petroleum, would not all C14 have disappeared millions of years ago?

  Yes, so it wouldn't be measurable -- past 50,000 years old is "infinite age", and millions of years is the same as a hundred thousand. Measuring organic material contaminated by bitumen applied when the sample was deposited would give the wrong age. I've rephrased to clarify. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• Two Creeks Fossil Forest. The Holocene started, as you say, around 11,700 years ago, the end of the Younger Dryas. So how does the Valders ice readvance, presumably at the start of the Younger Dryas, help to determine the start of the Holocene? Ah the date of the fossil forest is given as 13,730 to 13,550 cal BP, well before the start of the Younger Dryas c.12,900 BP, so apparently it is nothing to do with the YD. I am confused.

  Looking at the case study it's apparent that the readvance was known to be of short duration, so dating the forest would give a reasonably close marker for the end of the Pleistocene, because the readvance was known to be the last before the end of the ice. Before the radiocarbon dating the fossil trees were dated to 19,000 to 24,000 years ago by stratigraphic methods. So an accurate date for the forest pinned down the ice readvance date, and since that did not last long, it helped pin down the start of the Holocene too. I don't know if the Valders readvance is associated with the YD; I don't see that in the discussion in Taylor & Bar-Yosef, but it may be the case. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

  It can only have been one of many steps in dating the start of the Holocene and its relevance is unclear. I would delete. If you want an example of an interesting controversy, how about the re-dating of the end of the Neanderthals, which you refer to? Dudley Miles (talk) 10:34, 3 April 2015 (UTC)

  I picked this because it's one of the case studies Taylor & Bar-Yosef chose, and I felt that it was good to have a secondary source validating that this really is an important study. I'm not sure I understand your concern -- the source is unequivocal that the Two Creeks forest is a key part of Pleistocene/Holocene boundary dating in North America. They say: "The period during which the readvance and destruction of the Two Creeks forest occurred became identified as one of the terrestrial geological markers documenting events associated with the end of the Pleistocene". I agree that this would have been just one of many studies identifying the boundary; the overall definition of the end of the Pleistocene presumably required scores of results to be assimilated into a single picture of the global changes. That would apply to any result I could cite, though. Would it help if I clarified in the text that this was only one of the studies that are relevant to the boundary definition? The source doesn't say that, but I think it's uncontroversial enough to not need a separate cite. Mike Christie (talk - contribs - library) 18:24, 4 April 2015 (UTC)

  According to the quote the period - not the ice advance itself - is one of the markers associated with the end of the Pleistocene. This seems to me vague to the point of vacuity, not identifying Two Creeks as a key marker of the end. And no wonder as it was 2000 years earlier. Maybe we just have to agree to disagree on this. Dudley Miles (talk) 21:31, 4 April 2015 (UTC)

  Well, maybe, but I'd like to try to pin this down if possible. I don't understand your "2000 years" comment; are you referring to the duration of the Valders ice readvance? Mike Christie (talk - contribs - library) 21:56, 4 April 2015 (UTC)

  As you say at the beginning of the paragraph, the Pleistocene ended around 11,700 BP. You give a date for Two Creeks as 13,730 to 13,550 BP. My point is that I do not see how an ice advance c. 13,700 BP is key in determining the date of an ice retreat around 11,700 BP, 2000 years later. It tells you that the transition must have been later than 13,700 BP, but it does not give any evidence whether the Pleistocene ended 12,000 BP or 6000 BP. If Two Creeks disproved a generally accepted date for the end of the Pleistocene of, say, 20,000 BP, then it would have been a step in determining the date, but in that case you would need to explain the context, which you have not done. Dudley Miles (talk) 23:13, 4 April 2015 (UTC)

  If you have time, would you take a look on Google Books at Nature's Clocks by Doug MacDougall? Pages 91-97 discuss Two Creeks in detail, giving the history and importance of the site in dating glacial chronology. The bar chart included there leaves no doubt that the site is regarded as a critical marker of the end of the Pleistocene, and one of the most important radiocarbon results in geology. I understand your comment about the date only providing a terminus post quem, but it seems that's exactly what the importance of the site is -- it dated "the last surge of Wisconsin glaciation" and showed that it was thousands of years later than had been previously supposed. Is the problem that the article doesn't reflect this? The article does mention the previous consensus date of 19ka to 24 ka BP; what if I add a sentence to the end of the paragraph, saying that this result forced a reassessment of the dating of the end of the Pleistocene in North America? The MacDougall is less detailed on the radiocarbon dating that Taylor & Bar-Yosef, but it does get more specific about the reasons why the site is so important, so I would cite it as well as the Taylor & Bar-Yosef. Mike Christie (talk - contribs - library) 12:21, 5 April 2015 (UTC)

  So before the era of C14 dating the Pleistocene was thought to have ended before 20,000 BP, but Two Creeks showed that glaciations continued for thousands more years. I think you need to explain the wrong Pleistocene end date at the start of the paragraph, as without that it is unclear (to me) why Two Creeks matters. (You currently only explain that the Two Creeks date was wrong.) BTW it is off topic but it is curious that the ice advance occurred at about the time of the Older Dryas, but there was no advance during the far more severe Younger Dryas. This appears to be discussed at [2] but unfortunately only an abstract is currently available. Dudley Miles (talk) 15:23, 5 April 2015 (UTC)

  I added a couple of bits from Macdougall to try to address this; now that I understand your point I agree it wasn't clear. How does it look now? Mike Christie (talk - contribs - library) 17:04, 5 April 2015 (UTC)

  "and hence this was taken to be the date of the end of the Wisconsin glaciation, marking the end of the Pleistocene in North America" This is not quite right - as you say above it was not the end but the terminus post quem, the date of the final ice advance of the Wisconsin glaciation.

  Changed to "and hence this was taken to be the date of the last advance of the Wisconsin glaciation before its final retreat marked the end of the Pleistocene in North America"; I'd like to avoid using terminus post quem, as it's jargon that many readers won't understand. Mike Christie (talk - contribs - library) 20:25, 5 April 2015 (UTC)

  Dates such as 11,404 BP may confuse some readers, particularly as you have said above that the Pleistocene ended 11,700 years ago. I think you need to remind readers that the development of calibration led to a major revision of Libby's early dates. (It is strange that McDougall says that the calibration was only a few hundred years, which would put it around the same date as the start of the Holocene warming. Is this an error or has thinking changed that much since he wrote in 2008?)

  Very good point; I've added some clarification. Let me know if that addresses the issue. Re Macdougall: that looks like a flat-out error to me. Taylor & Bar-Yosef make it clear calibration pushed the date back by about 2,000 years. Macdougall may have been looking at the uncalibrated dates from the 1990 results, which were indeed a few hundred years different from Libby's original results. Mike Christie (talk - contribs - library) 20:25, 5 April 2015 (UTC)

• I have the impression that there is a "gap" between C14 dating and other methods for older dates, so that for example it is difficult to date a sample of c.150,000 years BP. Is this correct?

  That was probably true at one time, but it appears not to be the case now. Take a look at this book; figure 1.6 (near the end of chapter 1) gives a chart showing the effective ranges of various dating methods, and you can see there are other methods. I've no doubt an archaeologist would be able to give more details on where various methods fall short, of course. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

• A very fine article. I did not understand the equations, but they no doubt are useful to more mathematically literate readers. Dudley Miles (talk) 22:48, 31 March 2015 (UTC)

  Mike I added a couple of comments just below the radiocarbon/uncalibrated discussion. Dudley Miles (talk) 10:34, 3 April 2015 (UTC)

  I think I've responded to everything; let me know if there's anything outstanding. Mike Christie (talk - contribs - library) 18:27, 4 April 2015 (UTC)

See my reply above and there are a couple of points you have missed so I have moved them to here:

• "This is done by calibration curves, which are described in more detail below." Do you still need this? If so I think you should indicate which section you mean. Dudley Miles (talk) 22:48, 31 March 2015 (UTC)

  You're right, this is no longer needed. Cut. Mike Christie (talk - contribs - library) 21:56, 4 April 2015 (UTC)

• "the level of 14C in the biosphere has remained constant over time" Would it not be better to refer to the atmosphere as you point out below that biosphere level is determined by that in the atmosphere? Dudley Miles (talk) 22:48, 31 March 2015 (UTC)

  Yes, done. Mike Christie (talk - contribs - library) 21:56, 4 April 2015 (UTC)

• That looks fine to me. I will do a final read through tomorrow, but meanwhile how about this sentence: "During its life, a plant or animal is exchanging carbon with its surroundings, so the carbon it contains will have the same proportion of 14C as the biosphere and the carbon exchange reservoir." This sounds a bit odd to me. As the biosphere is the zone of life, it seems to say that life will have the same 14C as the zone of life. Do you mean atmosphere? Also it might be better to leave out the carbon exchange reservoir as you have not yet explained it at that point in the article. Dudley Miles (talk) 21:23, 5 April 2015 (UTC)

  Done. I was trying to avoid saying atmosphere because animals, for example, don't get their carbon directly from the atmosphere they get it by eating plants or other animals. But ultimately it does come from the atmosphere, so on reflection I think it's better to say so. I mentioned the carbon exchange reservoir because that includes the atmosphere, but if I just say atmosphere it's more accurate, and as you say it has not yet been explained. Mike Christie (talk - contribs - library) 21:37, 5 April 2015 (UTC)

Further comments

• "The sample is assumed to have originally had the same 14C/12C ratio as the ratio in the biosphere" Is this right? As different parts of the biosphere have different ratios, surely there is no such thing as the biosphere ratio.

  Changed. I was trying to get readers to think of the equivalent live organism, rather than the atmospheric source of the carbon, but as you say that introduces confusion so I think "atmosphere" is better. Mike Christie (talk - contribs - library) 01:10, 8 April 2015 (UTC)

• Carbon exchange reservoir. I think it would be helpful to start this section by defining it, before going on to say how the different elements vary. Also you seem ambiguous whether there is one reservoir or several. In the diagram you use the plural for the heading and the singular for the note.

  I've added a definition and a reference for it. Re the singular and the plural: the word "reservoir" is used to refer to both the overall reservoir, including the atmosphere, biosphere, and oceans, and also to refer to the individual components within that -- so the oceans are a reservoir. I was hoping this would be clear from context; is there a clarification that would help? Mike Christie (talk - contribs - library) 01:10, 8 April 2015 (UTC)

  I would just add a statement saying what you say above - that reservoir is sometimes used to mean the system as a whole and sometimes the individual components. Dudley Miles (talk) 18:11, 8 April 2015 (UTC)

  Done, along with another clarification per hamiltonstone's comments below. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• New Zealand/Austria graph. As with many maps and graphs, I find it difficult to tell apart the colours as I am colour-blind. Would it be possible to use contrasting primary colours?

  This is one of the parts of the article that predate my involvement, so I can't immediately reproduce this. However, the editor who made it was active recently on the German Wikipedia, so if you can let me know two colours which work well for people who are colour-blind, I'll ask them to do another version of it. Mike Christie (talk - contribs - library) 01:10, 8 April 2015 (UTC)

  I am not sure as there are different forms of colour blindness, but I think the blue is fine, and red and black should be OK for the other colours. It would help to make the lines in the key thicker.Dudley Miles (talk) 18:11, 8 April 2015 (UTC)

  I'll ask the editor to do a revised version. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• "It was quickly apparent that the principles of radiocarbon dating were valid, despite discrepancies the cause of which was then unknown." the cause of which were then unknown?

  I think it's "was": the subject is "cause", not "discrepancies". I thought about changing this to "causes", but really there was one primary cause, which was the need for calibration, so I'd rather not get the idea that there were lots of causes into the reader's head at this point. Mike Christie (talk - contribs - library) 01:10, 8 April 2015 (UTC)

  I do not see the logic of this. Calibration has two different components, variable C14 levels and the wrong half life, and you explain many other important causes of false dates. Dudley Miles (talk) 18:11, 8 April 2015 (UTC)

  OK, changed. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• Looks fine. Just a few minor points. Dudley Miles (talk) 10:26, 6 April 2015 (UTC)

Support. A very fine article on an important subject. Dudley Miles (talk) 09:23, 9 April 2015 (UTC)

Comments

• intro should mention that Libby got a Nobel explicitly for this work

  Done. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

• do all living organisms exchange their carbon well? for example a 6000-yr old tree has the same C14/C12 ratio as its reservoir?

  Yes, all living organisms exchange their carbon in a way that captures the then-current ratio, but a tree only exchanges carbon for the tree ring it is currently growing. So a 6,000-year-old tree has 5,999 rings that are not exchanging carbon, and one ring that is exchanging carbon. That's the basis of using the dendrochronology to establish the calibration curve -- each tree ring captures the ¹⁴
  C/¹²
  C ratio of the year it grew in. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

Perhaps mention this after "once it dies" in Principles (could be a footnote). Non-experts would have a hard time getting this. Nergaal (talk) 23:47, 27 March 2015 (UTC)

Done; I put this in the atmospheric variation section, which is where the use of tree rings for calibration is discussed. Mike Christie (talk - contribs - library) 16:06, 29 March 2015 (UTC)

• this is a bit confusing: "the radiocarbon age of marine life is typically about 440 years." this means if a fish is tested he appears to have died at the same time with a land-mammal dying 440 years ago?

  That's correct. The calibrated age doesn't show this, because marine life is calibrated with a different curve, to allow for exactly this problem. But if you catch a fish today, and test it as if it was a land animal, you'll get an apparent age of over 400 years. This actually came up in today's featured article, on the exhumation of Richard III -- he ate enough sea-food that the lab that tested his bones had to apply the marine correction to their results. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

Please add this clarification somewhere in the text. I hat to think really hard to get that this is what the sentence was saying. Nergaal (talk) 23:47, 27 March 2015 (UTC)

Done, inside the footnote that was already there. Mike Christie (talk - contribs - library) 16:06, 29 March 2015 (UTC)

• "Dates are often reported in years "before present", or BP; this refers to a baseline of 1950 AD, so that a date of 500 BP means 1450 AD." is a bit confusing, since present is not 1950. Maybe remove this from the intro?

  I actually added it at someone else's request; see above -- the suggestion was that people would want to know what a reported date means, and the BP terminology is very widely used, so I figured I should include it. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

then change "this refers" to "however, this actually refers". Nergaal (talk) 23:47, 27 March 2015 (UTC)

Done -- I just used "actually"; I don't think we need "however" as well. Mike Christie (talk - contribs - library) 16:06, 29 March 2015 (UTC)

• maybe the intro can mention that the nuclear tests and fossil-fuel burning has had a noticeable effect on the C14 distribution in the atmosphere?

  Done. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

Nergaal (talk) 18:15, 23 March 2015 (UTC)

@Nergaal: Sorry about the slow replies; I've responded to all your comments above. Mike Christie (talk - contribs - library) 01:55, 26 March 2015 (UTC)

• The article seems a bit dry now, how about spicing it up with File:Carbon_14_formation_and_decay.svg, File:Willard_Libby.jpg, File:Prometheus_tree1.jpg, File:Shroudofturin1.jpg and some pic of an old geiger counter? Nergaal (talk) 23:47, 27 March 2015 (UTC)

  I agree it could use more images. I had to remove the Libby picture because it's non-free, sadly. The equation used to be in the article; I took it out partly because I didn't need the third part of the equation, but mostly because it was better to be able to place text in between the two equations as part of the explanatory flow. The bristlecone pine picture is good, but unfortunately the two places in the article where it could go already have graphic images and there's not really room to add it. I'm not keen on putting the Shroud of Turin in; I think it's a somewhat controversial topic and I would rather find an image of one of the other archaeological examples. I found an image of the Great Isaiah Scroll and added that to the discussion of the Dead Sea Scrolls. I also agree that a picture of some of the measurement equipment would be good, but although I have access to some pictures of Libby's early equipment, they are copyrighted, and I don't think I can justify use. I'm open to other ideas -- it would be great to add more pictures.

  @Nergaal: I've responded to all your points above. Mike Christie (talk - contribs - library) 16:20, 29 March 2015 (UTC)

Put the tree after Intcal_13_calibration_curve.png. Maybe use File:Scintillation counter as a spectrometer.jpg or File:Scintillation Counter.jpg. Nergaal (talk) 21:45, 29 March 2015 (UTC)

I put the tree at the top of that section and moved the graph down, and trimmed the caption slightly (it was repeating material from the main text). Rather than a scintillation counter I went with an accelerator mass spectrometer, since AMS is now the most important measurement technology. How does it look now? Mike Christie (talk - contribs - library) 22:21, 29 March 2015 (UTC)

• One final thing: wherever you use BP, please also add the BCE date. Nergaal (talk) 22:25, 29 March 2015 (UTC)

  Done. In the Two Creeks discussion, I only added it to the final number, because I think it would get very messy to include parenthetical BC dates for each of the other six BP dates in that paragraph. Mike Christie (talk - contribs - library) 22:37, 29 March 2015 (UTC)

• Support I went through this article several times in the past year and I think it is of a very good quality. It is slightly over'y technical at times, but I have a hard time seeing how it can be improved even further considering the subject itself is very technical. If you have some time I would appreciate any comments at the FLC of List of nearest exoplanets. Nergaal (talk) 23:41, 29 March 2015 (UTC)

  Thanks for the review and support. I'll be glad to look at the FLC, but it might take me a day or two to get there; I have a couple of other commitments. Mike Christie (talk - contribs - library) 00:36, 30 March 2015 (UTC)

Comments from Freikorp

• Firstly just a disclaimer, my knowledge of the scientific world ends with the C average I got across a dozen odd science based units in my undergraduate degree, and that was several years ago, so this review will be largely non-technical.
• Consider wikilinking Before present; even though there is an explanation of the basics here there is a decent article on the subject.

  Done. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

• Any particular reason the third and fourth use of half-life are wikilinked, but the first isn't? Also despite the explanation a wikilink probably wouldn't hurt in the lead.

  Fixed; it was just an oversight. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

• Liquid scintillation counting is wikilinked, and in the below section "beta counting" is also linked to that page. The term "beta counting" does not appear at the 'Liquid scintillation counting' page; i'm confused.

  I've removed the second link. Liquid scintillation counting can be used to count either alpha particles of beta particles. I don't think a link from beta counting is necessary, though, since as you say it's linked earlier. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

• "Higham and co-workers (2014) have suggested..." Is it customary to format the date of the paper like this? Shouldn't it just read "In 2014, Hingham and co-workers suggested..."

  Fixed. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

• The very last sentence contains 3 duplicate links. Are they all necessary?

  Can you clarify? I clicked through all of them and unless the drugs I'm on are stronger than I think they are they all go to different articles. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

  Thermoluminescence dating, Varve and Dendrochronology are all wikilinked in the last sentence as well as earlier in the article. Dendrochronology is wikilined as "study of tree rings". Freikorp (talk) 04:00, 31 March 2015 (UTC)

• I made a few minor fixes.
• I'd agree that for an article on an extremely technical subject, the readability here is good.
• If you'd like me to comment on any thing in particular, just point it out. I'll support on prose once the issues above that require responses are addressed. Freikorp (talk) 08:54, 28 March 2015 (UTC)

  @Freikorp: Thank you very much for the review. Since you don't have a science background, there is one thing I'd like you to comment on, if you wouldn't mind; Johnbod mentioned at the start of this FAC that he thinks the article structure gets into the science too quickly. Could you have a look at his comments and see what you think? Thanks. Mike Christie (talk - contribs - library) 16:41, 29 March 2015 (UTC)

  The article does get very sciency fairly early at 'Physical and chemical details', but it's not like I wasn't expecting it to. It's probably true that if 'explanation of how radiocarbon dates' or the like appeared first less readers would be lost, but I don't see this as a major issue. I mean, how many people are going to be reading this article out of general interest unless it was TFA anyway? And it's not like they can't just scroll past the parts that are loosing them. The article certainly does 'recapitulate the theory as it has developed', but I don't see a problem with that either; if you're not interested in the development of the theory, again you can just skip those parts. I'm not saying couldn't be organised better or trimmed in parts, but I didn't see any major issues reading the whole thing (other than it was a bit dry as the subject didn't interest me too much haha). Freikorp (talk) 02:01, 1 April 2015 (UTC)

  Glad to hear it; thanks for taking a look. Mike Christie (talk - contribs - library) 01:08, 2 April 2015 (UTC)

Source review - spotchecks not done

• Check alphabetization of Sources
• Is Post 2001 or 2010? Nikkimaria (talk) 16:43, 4 April 2015 (UTC)

Both fixed. Thanks for the review. Mike Christie (talk - contribs - library) 17:33, 4 April 2015 (UTC)

SupportComments. Challenging subject, generally well done.

• There is no explanation offered to the reader to explain why they are being told about a thing called the "carbon exchange reservoir". I didn't really get what the point of the information was - it certainly isn't made explicit. Where the section comes close to explaining it, instead it veers into the weird: "the radiocarbon age of marine life is typically about 440 years". I think this section needs a sentence or more at the start to explain that although C14 decays at a constant rate, the proportion in a living creature depends on where in the biosphere it formed, lived and died. This is because the mixing of C14 that is created in the atmosphere into other parts of the biosphere, such as the oceans, can take varying amounts of time. If indeed that is the point being made...i was genuinely unsure.

  Your understanding is correct; I've added an explanation to that effect -- let me know if that does it. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• The section "Pleistocene/Holocene boundary in Two Creeks Fossil Forest" is a bit tricky, and I can see from comments above that it has already been the subject of some discussion. Although "varve" has been wikilinked in a previous section, i'm not sure its use without a plain English explanation is a great idea. I have an admittedly very rusty degree in geology and couldn't remember coming across the term. What about something like "Before the advent of radiocarbon dating, the fossilized trees had been dated by correlating sequences of annually deposited layers of sediment at Two Creeks with sequences in Scandanavia. This led to estimate that the trees were between 24,000 and 19,000 years old..."

  I like that wording. Done. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• "...which when calibrated gives two date ranges: 13,730 to 13,550 cal BP, or 11,780 BC to 11,600 BC". The expression "two date ranges" here implies that the two are different to each other, not different expressions of the same date range. I think this will mislead the reader. What about simply saying "...which when calibrated gives a date range of 13,730 to 13,550 cal BP, or 11,780 BC to 11,600 BC."

  Ouch. That was a bad editing error on my part; I was responding to an earlier comment about clarifying the fact that an uncalibrated date range could turn into two separate calibrated ranges, and misread the text when I made the edit. This is a single range and I've removed the incorrect wording. Mike Christie (talk - contribs - library) 01:14, 9 April 2015 (UTC)

• I have some sympathy for an early comment by Johnbod about the article becoming very technical, and I've often felt that a number of WP articles lack sufficient introductory or contextual material in the early body text (particularly in biology). However, in the case of this article, i can't think of an alternative approach that would better deliver the material without creating a choppy ordering of the content, so I'm satisfied that the current approach, particularly with the strong lead, is OK.

Great work Mike. hamiltonstone (talk) 12:43, 8 April 2015 (UTC)

• Closing note: This candidate has been promoted, but there may be a delay in bot processing of the close. Please see WP:FAC/ar, and leave the {{featured article candidates}} template in place on the talk page until the bot goes through. Ian Rose (talk) 05:42, 12 April 2015 (UTC)

The above discussion is preserved as an archive. Please do not modify it. No further edits should be made to this page.