Difference between revisions of "Template:Is this date calibrated?"
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Latest revision as of 09:29, 9 January 2019
For boxes that can be placed at the top of an article or section, see Template:Clarify radiocarbon calibration and Template:Clarify radiocarbon calibration in section.
- 1 What is radiocarbon calibration?
- 2 Usage
- 3 How to respond to this tag
- 4 Determining whether a cited date is calibrated or not
- 5 Example
- 6 Tracking category
- 7 Redirects
- 8 References
What is radiocarbon calibration?
For a variety of reasons, archaeological dates obtained with the method of radiocarbon must be calibrated to be correctly interpreted. This is important, for there can be differences of up to 4000 years between an uncalibrated date and its calibrated counterpart. For instance, one of the earliest putatively Iberomaurusian dates is 21,240 ± 130 14C BP (Tamar Hat, OxA-27506, Hogue and Barton 2016). This date is uncalibrated and calibrates to 25,845-25,270 cal BP (95.4% confidence) with the IntCal 13 calibration curve.
Unfortunately, dates reported in the literature are not systematically calibrated, nor systematically left uncalibrated. It is often difficult to figure out whether a given date in a book or scientific article is calibrated or not. When writing the encyclopedia, it is nevertheless crucial to figure this out. This allows calibrating dates for Wikipedia if this has not already been done by the cited author, and then specify that the date given in the Wikipedia article is calibrated, using "cal BP" instead of the ambiguous "BP".
This template is used to identify radiocarbon dates that are cited without specifying whether they are calibrated or not. On Wikipedia, it is preferable to cite dates in their calibrated forms, because calibrated dates correspond to the dates of the Gregorian calendar.
How to respond to this tag
This tag is a request to confirm that a given radiocarbon date is presented as calibrated.
Responding to this tag involves four steps.
- 1) Make sure that the date is indeed a radiocarbon date. Dates cited as 50,000 BP or more can be assumed to be non-radiocarbon dates, because that is the limit of the radiocarbon dating range. To the contrary, almost all dates younger than 50,000 BP will be found to be radiocarbon dates.
- 2) Determine whether the radiocarbon date is presented as calibrated or uncalibrated (see next section).
- 3) If it is found to be uncalibrated, calibrate it using, for instance, the OxCal Firefox extension. This will give a range of possible dates (e.g. 25,845-25,270 cal BP). You may decide to round it (e.g. "c. 25,600 cal BP").
- 4) Specify inline that the date is now calibrated. Do this by writing "cal BP" instead of "BP".
Determining whether a cited date is calibrated or not
The following can help determine whether dates given in the literature are calibrated or not. Even with this key, it is sometimes not possible to determine whether this is the case. An editor that cannot resolve whether a cited date is calibrated or not may very well consider removing the date from the article.
- 14C BP or uncal BP: the date is uncalibrated.
- cal BP: the date is calibrated. The "cal" in "cal BP" means "calendar years".
- BP: Used alone, this is often ambiguous, although there are at least five ways of resolving the ambiguity:
- 1) The source giving the date was published before 1998, when the IntCal98 calibration curve was published. In these cases, the given dates can be assumed uncalibrated.
- 2) The text specifies that all dates therein are either calibrated or uncalibrated. In practice, unless one is wiling to read much of the text, this is hard to verify.
- 3) The date is given with a margin of error. Almost always, uncalibrated dates use the plus-minus symbol (e.g. 21,240 ± 130 BP) and calibrated dates use the dash (e.g. 25,845-25,270 BP).
- 4) The laboratory number is given (e.g. c. 21,000 BP (OxA-27506)). In these cases, it is often possible to google the laboratory number and determine whether the cited date is calibrated or not.
- 5) If the date is referenced to have appeared in earlier publications, verify that reference and apply criteria 1 to 4 to that earlier publication.
Consider the following:<templatestyles src="Template:Quote/styles.css"/>
Step 1: Determine whether the date actually is a radiocarbon date
Is the date younger than 50,000 BP? If it is, it is almost certainly a radiocarbon date. (Radiocarbon dating is both considerably cheaper and more precise than other methods.) If it is older than 50,000 BP, it is not a radiocarbon date, because the range of radiocarbon dating is 50,000 years. It is hence not ambiguous to write "75,000 BP".
Very occasionally, one will encounter a non-radiocarbon date that is younger than 50,000 BP. For example Vermeersch (2000) gives a thermoluminescence date of 25,000 ± 2500 BP for the beginning of the Shuwikhatian culture of Egypt. In this case, one could format the date as "25,000 ± 2500 TL BP" so that a Wikipedian does not assume it is a radiocarbon date and wonder whether it is calibrated or not.
In the example above, the date is younger than 50,000 years, so it can reasonably be assumed to be a radiocarbon date.
Step 2: Determine whether the date is calibrated or not
In the example, the cited text (Palma di Cesnola 2001) is a French translation of a 1993 Italian book. It is therefore likely that dates therein are uncalibrated, since the original book was published before 1998. Nevertheless, it is possible that the dates were calibrated for the French translation, so the dates cannot be assumed uncalibrated. The text does not seem to discuss radiocarbon calibration, which is a hint, but not proof, that the date is not calibrated. The text gives neither a margin of error nor a laboratory number.
The text does refer for that date to two previous publications (Bartolomei et al. 1979, Bietti 1990). Because these two publications are earlier than 1998, it is probable that the date is uncalibrated. But it is best to verify, since the 2001 book might have secretly calibrated it. Verifying either of these two earlier publications confirms that the cited date of 20,000 BP is uncalibrated.
Step 3: Calibrate the date
Follow this step only if you have determined that the date is not calibrated. If it is calibrated, go to step 4.
This step assumes you use OxCal, which is available as a Firefox extension. You may also choose to calibrate dates in a different way. In OxCal, type "20,000" in the "date" field and use an artificial error (±) of 1 year. Choose a calibration curve, preferably the most recent IntCal curve, which should be the default. Click calibrate. You will see a bell curve and a note above it that reads:
24231 (95.4%) 23887calBP
The calibrated date is 24,231-23,887 cal BP. Change in the text the uncalibrated date for the calibrated date. The calibrated date notation is cumbersome and you may choose to round the preceding calibrated date to "c. 24,100" or "c. 24,000" cal BP.
Step 4: Specify inline that the date has been calibrated
So that other Wikipedians don't have to repeat steps 1 and 2, specify that the date given in the text is now calibrated. To make your calibration more easily verifiable, you may add a hidden comment in the source code:
<!--Calibrated using the IntCal13 calibration curve on 21 January 2022. Uncalibrated date: 20,000 ± 1 uncal BP (Palma di Cesnola 2001). Calibrated date: 24,231-23,887 cal BP.-->
The sentence now looks like this:<templatestyles src="Template:Quote/styles.css"/>
Pages with this template are added to Category:Articles that do not specify whether all their radiocarbon dates are calibrated or not (0)
- Palma di Cesnola, A. (2001). Le Paléolithique supérieur en Italie. (In French). Vol. 9. Préhistoire d'Europe. Grenoble: Éditions Jérôme Millon.
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