Can we assume constant C14 to C12 ratio in living tissues?

In summary, plants have a preference for C12 over C13 during photosynthesis, leading to a lower C13 to C12 ratio in plants compared to the atmosphere. The discrimination against C14 is minimal and can be corrected for using the C13 to C12 ratio. However, environmental factors such as changes in Earth's magnetic field and fossil fuel burning can affect the C14 fraction of carbon, leading to uncertainty in carbon-14 dating. This has been extensively studied in the journal Radiocarbon.
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wywong
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Plants prefer C12 to C13 during photosynthesis, so that the C13 to C12 ratio in plants is less than that in the atmosphere (by around 20% for most plants, but less difference in C4 plants like maize). Do plants discriminate against C14 too? If so, won't that cause a considerable uncertainty in carbon-14 dating?
 
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  • #3
Thanks jim mcnamara for your reply.

I find it hard to believe the same photosynthesis process discriminates against C13 but not against C14 which is heavier than C13. I did a google search and found this article:

https://www.cambridge.org/core/jour...e-for-13c12c/7034794E608EB5B6A3F8ED31D4FA38AD

If I understand correctly, the discrimination against C14 is more than twice that against C13, but the former can be more or less corrected for based on the later. That answers my original question.
 
  • #4
I think the the fractionation is about 2% (15 to 27 per mil). For 14C it is twice as much. In Radicarbon dating (and other 14C applications) , the 13C/12C ratio is used to correct for this effect.
 
  • #5
Well, looking at articles such as this one...
https://phys.org/news/2021-02-earth-magnetic-field-broke-years.html

...it seems that Earth's magnetic field has went through some tumultuous instability in the past. What happens when it weakens is that it allows a lot more of cosmic radiation to penetrate lower altitudes, and this again will increase the amount of atmospheric C14.

So there are points in the past where C14 cannot be assumed to have been whatever it is assumed to be today due to environmental reasons.
 
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The 14C fraction of carbon varies. The cosmonenic production changes (it is about 5 kilogram 14C per year) and the reservoir (the amount of carbon) changes. For instance by burning fosil fuel the amonunt of carbon as CO2 in the atmosphere increases and the 14C/12C ratio drops. This is the fossil fuel effect. The famous journal Radiocarbon has many hundreds of research articles dealing with this interesting question.
 
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1. What is the significance of the C14 to C12 ratio in living tissues?

The C14 to C12 ratio is significant because it is used to determine the age of organic materials through radiocarbon dating. This ratio is based on the fact that C14 is a radioactive isotope with a known half-life, meaning it decays at a predictable rate over time. By comparing the amount of C14 to C12 in a sample, scientists can estimate how long ago the organism died.

2. Is the C14 to C12 ratio constant in all living tissues?

No, the C14 to C12 ratio is not constant in all living tissues. This is because the amount of C14 in the atmosphere can vary over time due to changes in solar activity and other factors. Additionally, different organisms may have different levels of C14 in their bodies depending on their diet and environment.

3. How do scientists account for variations in the C14 to C12 ratio?

Scientists account for variations in the C14 to C12 ratio by using calibration curves. These curves are created by comparing radiocarbon dates from known historical events, such as tree rings, to the corresponding C14 to C12 ratios. This allows scientists to adjust for any changes in the ratio over time and improve the accuracy of radiocarbon dating.

4. Can we assume a constant C14 to C12 ratio in all samples when using radiocarbon dating?

No, it is not safe to assume a constant C14 to C12 ratio in all samples when using radiocarbon dating. It is important for scientists to take into account any potential variations in the ratio and use calibration curves to improve the accuracy of their results.

5. Are there any limitations to using the C14 to C12 ratio for dating purposes?

Yes, there are limitations to using the C14 to C12 ratio for dating purposes. Radiocarbon dating can only be used on organic materials that were once living, and it is most accurate for samples that are less than 50,000 years old. Additionally, contamination of the sample can affect the results, so it is important for scientists to carefully handle and prepare samples for testing.

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