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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

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?

nonbel 8y ago
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 https://en.wikipedia.org/wiki/Joseph_Justus_Scaliger
- fwip 8y ago
  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.
  - Godel_unicode 8y ago
    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.
  - nonbel 8y ago
    See my ref here for how radiocarbon dating is calibrated to dates attributed to historical artifacts: https://news.ycombinator.com/item?id=18694692 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 https://en.wikipedia.org/wiki/Chronology
crygin 8y ago
The C14 timeline is calibrated from radiocarbon years to calendar years: https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dates https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dat...
- nonbel 8y ago
  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-Chap13.pdf 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.
  - jimrandomh 8y ago
    No, this is incorrect. Per the Wikipedia article, there are many cross-checked calibration sources, but man-made artifacts aren't one of them.
    - nonbel 8y ago
      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_dates https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dat...
      - crygin 8y ago
        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 http://depts.washington.edu/qil/aboutqil.html Datasets: http://depts.washington.edu/qil/datasets/ http://depts.washington.edu/qil/datasets/
cpburns2009 8y ago
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.
- zeotroph 8y ago
  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.
- nitrogen 8y ago
  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.
acidburnNSA 8y ago
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 https://whatisnuclear.com/geology.html
InclinedPlane 8y ago
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).

nonbel 8y ago

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 https://en.wikipedia.org/wiki/Joseph_Justus_Scaliger

fwip 8y ago
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.
- Godel_unicode 8y ago
  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.
- nonbel 8y ago
  See my ref here for how radiocarbon dating is calibrated to dates attributed to historical artifacts: https://news.ycombinator.com/item?id=18694692 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 https://en.wikipedia.org/wiki/Chronology

crygin 8y ago

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

nonbel 8y ago
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-Chap13.pdf 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.
- jimrandomh 8y ago
  No, this is incorrect. Per the Wikipedia article, there are many cross-checked calibration sources, but man-made artifacts aren't one of them.
  - nonbel 8y ago
    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_dates https://en.wikipedia.org/wiki/Calibration_of_radiocarbon_dat...
    - crygin 8y ago
      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 http://depts.washington.edu/qil/aboutqil.html Datasets: http://depts.washington.edu/qil/datasets/ http://depts.washington.edu/qil/datasets/

cpburns2009 8y ago

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.

zeotroph 8y ago
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.
nitrogen 8y ago
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.

acidburnNSA 8y ago

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 https://whatisnuclear.com/geology.html

InclinedPlane 8y ago

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).