Hacker News new | past | comments | ask | show | jobs | submit login

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.



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.


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?


"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.


The half life of Carbon 14 is 5,730 years. So all it would be able to do is tell you the person is between 0 and 5,730 anyway right?

That wouldn’t help solve these cases.


No, the radioactive decay will follow a (nearly) continuous exponential curve. Half-life is just an arbitrarily chosen point on that curve: the point at which half of the atoms have decayed. With carbon dating you are basically solving this equation: percent of carbon 14 left = 0.5 ^ (years since death/5,730). If it has been 500 years since death, you would expect 94% of the original carbon 14 to remain.

That said, you generally have error boundaries spanning multiple decades and it measures since time of death (when new carbon stops being integrated into the body) not time of birth, so it would not be useful for this.


Note that you can use tooth enamel, which freezes its carbon at time of development (instead of death). https://news.ycombinator.com/item?id=20627335

That said, the error bars are simply too large to do anything reasonable for dates prior to 1955. The difference between 80 years and 110 years is 98.7% vs. 99.0% of the original C14 concentration... and while you may be able to get a very precise measurement of the remaining C14 you also need to very precisely know the baseline from that era to determine the percentage. Thus typical radiocarbon error bars are at least ±60 years.


Thanks for the details.




Applications are open for YC Winter 2020

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact

Search: