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Thread: A Question About Carbon Dating

  1. #1
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    A Question About Carbon Dating

    How can we determine the half life of C14 is 5,730 (+ or -) years, when we haven't lived to see it? How is it quantifiable evidence without a longitudinal study where we actually observe it decaying and time-line the data?

    Another problem is the assumption that the rate of decay has been constant over the eons...

    Is there any accounting for unseen energy between two objects as well as radioactive changes in the atmosphere, global changes (ice age/slows decay and warmer climates which increases decay) and lastly anti-matter.

    Would any of those have an effect that would alter the decay time substantially enough to be relevant in the process.

  2. #2
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    Almost everything is subject to unreasonable doubt. We notice that 1% of the C14 decays in so many years, and 2% in so many years and 3% in so many years. We make a graph, drawing a curve between the data points, determine the algabraic formula for that curve and complete the curve out to about one million years. You are thinking correctly, the extrapolation is wrong if the strong force, or the weak force jumped to a slightly different value a few or many centuries ago. We don't think that happened as we have some independent means of dating things and they check reasonably close. Neil
    Last edited by neilzero; 2012-May-08 at 02:01 AM.

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    Quote Originally Posted by LoneTree1941 View Post
    How can we determine the half life of C14 is 5,730 (+ or -) years, when we haven't lived to see it? How is it quantifiable evidence without a longitudinal study where we actually observe it decaying and time-line the data?
    You don't have to measure decay over the entire half life, just the rate of decay and then extrapolate the half life from that.

    Another problem is the assumption that the rate of decay has been constant over the eons...
    We have never observed anything that changes the rate of decay and our theories don't suggest that external factors will change it.

    (Actually, there have been some small, unconfirmed annual variations reported but they don't matter to this.)

    Also, radiocarbon dating is correlated against various other methods (e.g. tree rings).

    Is there any accounting for unseen energy between two objects as well as radioactive changes in the atmosphere, global changes (ice age/slows decay and warmer climates which increases decay) and lastly anti-matter.

    Would any of those have an effect that would alter the decay time substantially enough to be relevant in the process.
    None of those affect the rate of decay (although changes in the atmospheric mix of carbon isotopes have to be accounted for).

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    Quote Originally Posted by LoneTree1941 View Post
    How can we determine the half life of C14 is 5,730 (+ or -) years, when we haven't lived to see it? How is it quantifiable evidence without a longitudinal study where we actually observe it decaying and time-line the data?

    Another problem is the assumption that the rate of decay has been constant over the eons...

    Is there any accounting for unseen energy between two objects as well as radioactive changes in the atmosphere, global changes (ice age/slows decay and warmer climates which increases decay) and lastly anti-matter.

    Would any of those have an effect that would alter the decay time substantially enough to be relevant in the process.
    neilzero already gave some answers, but there are other ways where C14 half life can be (and is) verified: tree rings. Each year leaves a telltale imprint of the weather/climatological conditions that year in the size of that year's ring. Those rings can be matched on long dead trees too. See this wiki article. The wiki article on C14 dating also lists some other methods for verification, like coral growth.

    ETA: Duh.. .beaten by Strange, but I got linkies!
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    Quote Originally Posted by LoneTree1941 View Post
    How can we determine the half life of C14 is 5,730 (+ or -) years, when we haven't lived to see it? How is it quantifiable evidence without a longitudinal study where we actually observe it decaying and time-line the data?
    We actually do observe it decaying and time-line the data. "Half-life" is just a convenient term used when discussing the decay rate of radioactive isotopes. C14 is hardly the only radioactive isotope in existence, some have half-lives of seconds, minutes, hours, etc.

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    95 miles an hour? But officer, I have only been driving for fifteen minutes!
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    Quote Originally Posted by LoneTree1941 View Post
    How can we determine the half life of C14 is 5,730 (+ or -) years, when we haven't lived to see it? How is it quantifiable evidence without a longitudinal study where we actually observe it decaying and time-line the data?
    I think it's been explained pretty well already. Going a bit further, we actually have calculations for the half-life of isotopes (128 tellurium) that are much longer (trillions of times) than the age of the universe. I'm not sure how that was calculated, but isotopes don't decay all at the same time (they're not like fruit, for example, which gradually decay), but decay at random. So if you put 1,000 atoms in a box and notice that one decays each day, then you can calculate the half-life from that. A similar process would be, suppose you have 100 dice and you toss them all at once. You notice that about one-sixth show a 1. You can guess that the chance of rolling a 1 is 1/6, even without rolling a single die many times.
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    A lot of information about radionuclide dating in general - including discussion about that "assumption about constant decay rates":
    http://www.rationalskepticism.org/cr...ous-t1783.html
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    I appreciate all the answers; they're all very helpful to me!

    LT

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    Quote Originally Posted by Jens View Post
    ... we actually have calculations for the half-life of isotopes (128 tellurium) that are much longer (trillions of times) than the age of the universe. ...
    And looking at the other end, there are lots of isotopes with half-lives much shorter than a human lifetime, and we have measured the samples to extinction (many half-lives). As a side issue to a project I was on 37 years ago, I used equipment to count the photons from the decay of Gold-192 (about five hour half-life) over 10 half-lives many times. There was never a statistically significant deviation from perfect half-life curves. I did the same for scores of isotopes in the 190-200 mass range, but I give this as an example to show that while we haven't measured C-14 for more than one half-life, we are applying a broader idea.
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