Two Chinese Stalagmites Are a 'Holy Grail' for Accurate Radiocarbon Dating | Hacker News Reader

Two Chinese Stalagmites Are a 'Holy Grail' for Accurate Radiocarbon Dating

gizmodo.com

105 pointscurtis25 comments

Open articleView on HN

Original paper links

Science (subscription required): http://science.sciencemag.org/content/362/6420/1293

SciHub: https://sci-hub.tw/10.1126/science.aau0747

Wouldn't Rosetta Stone be a better metaphor than Holy Grail?

"Holy grail" is being used as an idiom and not a metaphor here.

Idioms are colloquial metaphors

No, they are not. The meaning of an idiom is not predictable from its constituent words, that’s it. A metaphor involves some kind of meaning transfer. In this case some properties of the ‘prototypical’ Holy Grail (desirability mostly) are transferred to the stalagmites. The source for the transfer itself could potentially be an idiom, but in this case it’s not, actually. The word ‘grail’, albeit rare, has a normal meaning (a kind of cup), and ’holy grail‘ is what it is: a holy cup. We just decided based on the strength of the literary tradition to call a particular object that way.

It would. They got the accomplishment (“A precise and accurate C14 calibration is considered the Holy Grail of radiocarbon dating”, from the original paper) and the means necessary for it mixed up.

Finding the means necessary to an accomplishment is in itself an accomplishment.

If their work was to search for perfect samples then the accomplishment was finding them. If their work was in calibration then the samples are just a mean.

Maybe in the last decades everyone knew that good stalagmites were needed and so people were searching for the perfect ones.

It is all a matter of what story are you trying to tell.

So... how do people actually know how much C14 was in something? Does dating only work if you know how much C14 was there originally? Otherwise how would you be able to measure the difference between what is there and what was there originally?

They calibrated it to the amount of C-14 found in artifacts with "known" dates, eg from ancient egypt. Most of those "known" dates originally come from this guy: https://en.wikipedia.org/wiki/Joseph_Justus_Scaliger

Are you sure you linked the right page? It contains no mentions of carbon dating, nor does it seem to indicate that he was involved in determining the date of ancient artifacts.

GP is saying that the article is about the person who established a lot of known dates. Those known dates are then used by others to establish the C14 baselines.

Two distinct but related facts.

See my ref here for how radiocarbon dating is calibrated to dates attributed to historical artifacts: https://news.ycombinator.com/item?id=18694692

Joseph Scaliger is just like the "founder of modern chronology":

>"The last great chronographer was Joseph Justus Scaliger (1540-1609) who reconstructed the lost Chronicon and synchronized all of ancient history in his two major works" https://en.wikipedia.org/wiki/Chronology

The C14 timeline is calibrated from radiocarbon years to calendar years: https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dat...

At the most fundamental level, the radiocarbon date is calibrated to the historical dates given to ancient artifacts: http://www.amarnaproject.com/documents/pdf/ocr/Binder12-Chap...

There are additional levels of calibration above that one, but that is the main way the dates are arrived at.

No, this is incorrect. Per the Wikipedia article, there are many cross-checked calibration sources, but man-made artifacts aren't one of them.

How do you account for the source I provided that describes exactly what they did?

Also, here is what wikipedia says:

>"Although Willard Libby, the inventor of radiocarbon dating, had pointed out as early as 1955 the possibility that the 14C/12C ratio might have varied over time, it was not until discrepancies began to accumulate between measured ages and known historical dates for artefacts that it became clear that a correction would need to be applied to radiocarbon ages to obtain calendar dates." https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dat...

I worked on this with Minze Stuiver -- the goal was to eliminate reliance on man-made artifacts of potentially ambiguous date. About the project: http://depts.washington.edu/qil/aboutqil.html

Datasets: http://depts.washington.edu/qil/datasets/

>"14C, as stored in tree rings, is being measured to accurately determine the atmospheric 14C levels of the last 10000+ years. This is essential in getting precise dates for historic and prehistoric materials."

Can you explain more how this removes dependence on historical dates? Tree rings need to be calibrated too since more than one can form per year or years can be skipped based on the weather (too cold or too little precipitation -> growth stops).

I’m not sure I understand the question. Dendrochronology is independent of historical records, because you can start with a freshly-cut tree or core sample and work backwards to date an older sample. This is highly accurate and does not depend on records of when a tree was cut down. Yes, it is possible for rings to be ambiguous, but literally every measurement technique has error.

You then use the samples dated with dendrochronology to calibrate your radioisotope dating.

>"you can start with a freshly-cut tree or core sample and work backwards to date an older sample. This is highly accurate and does not depend on records of when a tree was cut down."

Assuming that the matching of rings is done perfectly (from my looking it up this is not trivial, where is the best place to find the raw data for one of the reference sequences btw?), I don't see how you could trust this without matching some rings to wood from known artifacts to "check it".

I mean can't you get a decade-long drought and so miss 10 years? And here is a source reporting that missing rings become more frequent as you look back further (it grows to 6% missing at 150 years): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4885872/

Of course that all depends on the species, etc so maybe it can be avoiding by only selecting the "right" samples. Can you share a good source where I can see how one of the reference sequences has been arrived at from scratch?

The idea is the level of C14 in the atmosphere is constant, and living organisms will have about about the same ratio of C14 to C12. When they die they no longer replenish the C14 so the amount decreases over time as it decays (it's radioactive). You can then calculate how old something is based on the ratio of remaining C14 to C12. I'm not sure what the process is that relates C14 to stalagmite because it's inorganic.

And all the CO2 which is added to the atmosphere by burning ancient and practically C14-free carbon compounds makes using this isotope less reliable, so other measuring methods are required.

The article says they used thorium-230 dating to calibrate layered samples from the stalagmites. This cave was special because the stalagmites did not contain much carbon from limestone, but did include atmospheric carbon.

As others have stated radiocarbon measurements can be compared to calibrations to some degree. Along these lines, see also the isochron method, which uses the slope of a line to back-calculate the original isotopic concentration. The fundamental assumptions is that isotopic concentrations are uniform throughout a sample at the time of birth, but different elements solidify at different concentrations. So by looking at isotopic ratios around a sample you'll find higher concentrations of daughter nuclides where higher concentrations of parents once were. If you plot the data you can look at the slope and see the age. It's easier to see graphically [1].

[1] https://whatisnuclear.com/geology.html

Precisely, that's why these calibrations are so important.

You can start from the assumption that the natural C14 to C12 ratio is a constant. And from there you can measure the actual ratio in the present time for a sample. Using math you can estimate how long ago the material was part of a living creature, since in the meantime the ratio would not have kept pace with the natural environmental ratio and instead would change depending on the half-life of C14. However, the assumption of a constant natural abundance of C14 is incorrect, there are lots of complex effects (like solar activity) which impact the ratio, which in turn affects the estimated age of an object. The more data you have on ancient C14 ratios the better able you are to calibrate radiocarbon dating.

In the past ancient trees and lake/seafloor samples have been used because they have many individual samples from separate years, each of which can be independently dated (separate from radiocarbon analysis).

Reply on news.ycombinator.com