4 ms·

so it's time for Carbon-14 then ...

jerf 7y ago
Carbon-14 datings works because once an organism dies, it stops exchanging carbon with its environment, so C14 stops coming in. Carbon dating any living organism will come back with "it died 0 years ago/hasn't died yet", give or take whatever details make it more complicated in reality than it is in theory, as it always is.
- iguy 7y ago
  Is there any dead carbon, like perhaps in the teeth? Have never heard of it being done, but would be neat.
  - hobofan 7y ago
    Teeth mostly consist of hydroxyapatite, which doesn't contain any carbon. Not 100% sure, but for someone that just died, you might be able to do it with their brain, as brain cells are hardly ever renewed. For a living human I don't think there is any way that's non-invasive.
    - garmaine 7y ago
      That thing about brain cells not regenerating is a myth, btw.
      - hobofan 7y ago
        Could you provide a source for that? I recently tried to read up on the topic and everything I found stated that brain/nervous cells are generally barely regenerated and can stay with you your whole life. Granted, most articles trace back to this source[0] from 1967, but if newer information exists, they've done a really bad job at spreading it. [0]: https://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101940 https://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101940
  - 3JPLW 7y ago
    Apparently it is possible to do radiocarbon dating on tooth enamel. Enamel contains 0.4% carbon and is indeed frozen at time of development. Unfortunately, we're limited to post-nuclear testing because without the atmospheric diffusion C14 has very low precision due to the half-life of 5730 years. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957015/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957015/ https://www.nature.com/articles/437333a https://www.nature.com/articles/437333a
    - iguy 7y ago
      Thanks! That's interesting, to use the post-nuclear curve as a modern clock, instead of using C14's half life for an ancient clock. For a given tooth they seem to assume all enamel was from one date, during childhood.
- sbuttgereit 7y ago
  As I recall, there's also an issue with radio-carbon dating anything after atmospheric atomic weapons testing commenced.
  - Someone 7y ago
    That problem started earlier, when we started burning significant quantities of coal. https://en.wikipedia.org/wiki/Radiocarbon_dating https://en.wikipedia.org/wiki/Radiocarbon_dating: ”Research has been ongoing since the 1960s to determine what the proportion of 14C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age […] Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its 14C to decay below detectable levels, fossil fuels contain almost no 14C, and as a result there was a noticeable drop in the proportion of 14C in the atmosphere beginning in the late 19th century. Conversely, nuclear testing increased the amount of 14C in the atmosphere, which attained a maximum in about 1965 of almost twice what it had been before the testing began.”
not2b 7y ago
Nope. As long as you're alive, you're breathing and taking in C14 from the atmosphere (it's produced by cosmic rays turning N14 into C14). When you did you no longer breathe and the C14 decays. So radiocarbon dating measures the time from the death of the organism to the present. edit: ninja'd.
- shadofx 7y ago
  Maybe there's a part of the body that stops exchanging carbon with the lungs after a certain point? Like maybe the teeth or the corneas.
  - saalweachter 7y ago
    Assuming this worked, it seems a bit extreme. You want to validate the age of a person, so you remove one of their teeth or take a tissue sample from their eye?
    - logfromblammo 7y ago
      "The Orville" had an episode where an alien culture used a procedure that sampled teeth to determine the exact birthdate of a person. There's not much in the tooth apatite that would be useful for radiometric dating on the time scale of a single human lifespan, though. I don't think you could do it with radiometrics, no matter what you sampled. Anything precise enough to indicate one year within a range of 100 would probably kill the animal with its radiation, even if it were naturally common enough to be taken up by living organisms. It may be that a tooth is an easy source of original DNA, and approximate age may be extrapolated from accumulation of copy-error mutations in different types of cells in the body, which would be affected by the frequency of division. So by comparing DNA found in the tooth mineral against that found in the tooth nerve cells, and in the tooth blood supply, it might be possible to narrow the range of possible whole-organism ages by referencing mean mutation rates, and then further narrow it by checking telomere lengths. Seems like that might vary somewhat by individual, and their history of radiation exposure.
  - MBCook 7y ago
mighty_bander 7y ago
Oof, HN does not like jokes.

jerf 7y ago

Carbon-14 datings works because once an organism dies, it stops exchanging carbon with its environment, so C14 stops coming in. Carbon dating any living organism will come back with "it died 0 years ago/hasn't died yet", give or take whatever details make it more complicated in reality than it is in theory, as it always is.

iguy 7y ago
Is there any dead carbon, like perhaps in the teeth? Have never heard of it being done, but would be neat.
- hobofan 7y ago
  Teeth mostly consist of hydroxyapatite, which doesn't contain any carbon. Not 100% sure, but for someone that just died, you might be able to do it with their brain, as brain cells are hardly ever renewed. For a living human I don't think there is any way that's non-invasive.
  - garmaine 7y ago
    That thing about brain cells not regenerating is a myth, btw.
    - hobofan 7y ago
      Could you provide a source for that? I recently tried to read up on the topic and everything I found stated that brain/nervous cells are generally barely regenerated and can stay with you your whole life. Granted, most articles trace back to this source[0] from 1967, but if newer information exists, they've done a really bad job at spreading it. [0]: https://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101940 https://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101940
- 3JPLW 7y ago
  Apparently it is possible to do radiocarbon dating on tooth enamel. Enamel contains 0.4% carbon and is indeed frozen at time of development. Unfortunately, we're limited to post-nuclear testing because without the atmospheric diffusion C14 has very low precision due to the half-life of 5730 years. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957015/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957015/ https://www.nature.com/articles/437333a https://www.nature.com/articles/437333a
  - iguy 7y ago
    Thanks! That's interesting, to use the post-nuclear curve as a modern clock, instead of using C14's half life for an ancient clock. For a given tooth they seem to assume all enamel was from one date, during childhood.
sbuttgereit 7y ago
As I recall, there's also an issue with radio-carbon dating anything after atmospheric atomic weapons testing commenced.
- Someone 7y ago
  That problem started earlier, when we started burning significant quantities of coal. https://en.wikipedia.org/wiki/Radiocarbon_dating https://en.wikipedia.org/wiki/Radiocarbon_dating: ”Research has been ongoing since the 1960s to determine what the proportion of 14C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age […] Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its 14C to decay below detectable levels, fossil fuels contain almost no 14C, and as a result there was a noticeable drop in the proportion of 14C in the atmosphere beginning in the late 19th century. Conversely, nuclear testing increased the amount of 14C in the atmosphere, which attained a maximum in about 1965 of almost twice what it had been before the testing began.”

not2b 7y ago

Nope. As long as you're alive, you're breathing and taking in C14 from the atmosphere (it's produced by cosmic rays turning N14 into C14). When you did you no longer breathe and the C14 decays. So radiocarbon dating measures the time from the death of the organism to the present. edit: ninja'd.

shadofx 7y ago
Maybe there's a part of the body that stops exchanging carbon with the lungs after a certain point? Like maybe the teeth or the corneas.
- saalweachter 7y ago
  Assuming this worked, it seems a bit extreme. You want to validate the age of a person, so you remove one of their teeth or take a tissue sample from their eye?
  - logfromblammo 7y ago
    "The Orville" had an episode where an alien culture used a procedure that sampled teeth to determine the exact birthdate of a person. There's not much in the tooth apatite that would be useful for radiometric dating on the time scale of a single human lifespan, though. I don't think you could do it with radiometrics, no matter what you sampled. Anything precise enough to indicate one year within a range of 100 would probably kill the animal with its radiation, even if it were naturally common enough to be taken up by living organisms. It may be that a tooth is an easy source of original DNA, and approximate age may be extrapolated from accumulation of copy-error mutations in different types of cells in the body, which would be affected by the frequency of division. So by comparing DNA found in the tooth mineral against that found in the tooth nerve cells, and in the tooth blood supply, it might be possible to narrow the range of possible whole-organism ages by referencing mean mutation rates, and then further narrow it by checking telomere lengths. Seems like that might vary somewhat by individual, and their history of radiation exposure.
- MBCook 7y ago

mighty_bander 7y ago

Oof, HN does not like jokes.