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Carbon dating and half times

  1. Aug 17, 2006 #1
    The first half time of radioactive carbon (14C) that got some consensus is the Libby date of 5568 years, which is still used..

    See Wikipedia

    The latter is very fortunate, calibration tables, like the current INTCAL04, being independent of half times for determining age. So calibrated datings are 'correct' albeit with considerable margins. What is not correct however, with wrong half times, is the presumed original concentration of radiocarbon (delta14C) in the atmosphere and in the calibration table it can be seen that the concentration is assumed to increase strongly with age.

    This could be partly explained by the difference in atmospheric CO2 concentration, the speed of the carbon cycle and the production rate of 14C as function of the cosmic radioactivity. But a lot of those changes don't make sense and up until now, there have been little if any serious attempt to explain the strong variation in assumed 14C ratios. Could it be that the half time is wrong instead and that this accumulation of 14C is actually non existent?

    Such a simple explanation I did not even dare to challenge myself, expecting that determining halftimes involves advanced, well established physics, way above my perception. However:


    Consequently, The most suitable half time for radio carbon should be 6030 years. I do wonder if such a rebellion has even a remote change to get accepted in the most conservative environment ever.
    Last edited: Aug 17, 2006
  2. jcsd
  3. Aug 20, 2006 #2


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    Well one can certainly call into question the half-life of any radionuclide, but then one should have evidence to support one's contention.



    The half-life of Carbon-14 is approximately 5700-5730 years.

    The apparent ratio of C-14 to C-12 in the atmosphere is 1.3 x 10-12 and sensitivities of approximately 1 x 10-15 have been obtained.


    Also, it has occurred to me that perhaps the ratio of C-14 to C-12 in the atmosphere may vary, and could actually be lower if there was a source with a different (lower, and perhaps much lower) ratio. That source would be geologic, e.g. a volcano or melting glaciers in which the C-14 has decayed over several half-lives. Effects on C-ratio my be geographically local or regional.

    But were there such sources during the past 20,000-30,000 years or so?
  4. Aug 21, 2006 #3
    Well, let this be the evidence. (Source INTCAL04 Reimer et al)

    When recalculating the original delta 14C in the atmosphere, using the calibration tables, a strong linear trend is obvious which would dissapear if the half value of 14C was to be 6030 years instead of 5730 years.

    My guess is that volcanoes as source of depleted carbon is not that prominent. Nevertheless, volcanic tracers in the greenland ice cores do show a high activity throughout the last glacial transition around 20-10 Ky before past in contrast to the last glacial maximum and the Preboreal, suggesting a major tectonic active period.

    Here we compare the detrended delta14C (from the previous graph) with the d18O variation in the Greenland ice core (GISPII) which is (incorrectly) assumed to be temperatures. It may be clear why nobody really has attempted to explain all those spikes in the delta14C. We can speculate a little.

    The variation in 14C ratio also depends on variation in cosmic radio activity which is supposed to be correlated with the earth magnetic field. The last (sort of disputed) paleomagnetic excursion (field collapse) was the Mono Lake event at 26000 years BP, which also correlates with a strong 10Be spike in the ice cores. So that spike seems to be covered.

    Furthermore we observe that the stronger variation of delta 14C between 15Ky BP and 11Ky appears to correlate with the d18O spikes of the Bolling Allerod event and the Younger Dryas. As there is a strong fractination going on in the CO2 exchange between the oceans and the atmosphere. 14C dissolves much faster in water and outgasses slower than 12C. These periods are known to have strong changes in the thermohaline current which might have changed the CO2 exchange equilibrium between atmosphere and ocean which might explain the delta 14C spikes.

    All of this does not explain the 20-18 Ky spike. Concurrent with that event is the end of the Last Glacial aximum and the synchronous global warming, for what it is worth. I have also no idea about the recent increases in the Holocene at about 8000 years BP and 1400 years BP.
  5. Sep 3, 2006 #4
    Calculation of half-lives is normally based on the assumption that the particular atoms are unaffected by background radiation. In a laboratory setting this approach works, but in the real world radioactive decay will be affected by background radiation. Decay is measured in half-lives rather than atoms per time period, because the amount of the substance present affects the decay rate. 5 pounds of a 10 pound "chunk" of an element will decay in "x" years. 2.5 pounds of the remainder will decay in the next "x" years.

    Interaction with other radioactive elements is likely in the broader environment. This interaction may increase the number of radioactive isotopes of an element in an area or increase the rate of decay. I'm not sure what elements might produce carbon as a decay byproduct.

    The outside influences on radioactivity cannot be easily determined, however, it is likely that cosmic radiation varies in different areas of the galaxy with activity varying over thousands of years rather than just the relative handfall that scientists have been measuring it. Cosmic events that could produce radiation are relatively rare in earth's immediate neighborhood. You might check to see if the spikes you mention occurred during a time when earth was in a region where radiation from a supernova might have affected it.

    One reason I'm not enthusiastic about radiocarbon dating is the uncertainty about its accuracy. Another problem is that when dating burned wood the dating would show the age of the wood, not the date of the fire. Moreover, the outside or newest part of the wood usually burns first, so the wood might show a date a century or more before the fire.
  6. Sep 3, 2006 #5
    Well, another problem of dating charcoal is fractination during the oxidation. The heavier 14C isotopes resist more to oxidation. Consequently one has to correct for that, actually for any fractination process. For that the d13C value is used with even a lot more complications.

    But actually any radiologic dating method has it's own problems. Carbon dating is not necesarely inferior because of the complications. And if there is a real error of about 5% in the half time (not 5530 but 6030 years), what about the accuracy of other half times?
  7. Aug 28, 2010 #6
    Reviving this thread because of this News release of Stanford. It's now hypothesed that neutrinos could affect half life of unstable isotopes.

    That may be an understatement. Just about everything that relies on isotope dating techniques may need revision.

    I have always wondered about the difference in 14C half lives, Libby, (5568±30y), Cambridge ( 5730±40y), Jenks and Sweeton 1952 (6030±86y) as elaborated upon by Chiu et al. Could it be that all of them were right at the time?
    Last edited: Aug 28, 2010
  8. Aug 28, 2010 #7
    I've just joined this discussion and have read the new article w.r.t neutrinos affecting the half-life of 14C. The ice age dating of phenomena seems to go increasingly awry from around 10,000 years ago imo. I have a pet theory that this is linked to the 3D orbit of the Earth relative to the ecliptic (rotational plane) of the Sun's inner core. Imagine an asymmetric neutrino emitting innermost core of the Sun. As the Earth's inclination orbit varies, it will rise above and below the Sun's innermost core ecliptic. This could give an increase in the number of incident neutrino particles, so increasing the decay rate of 14C. Relative alterations to the carbon dating adjustment scale should improve correlations of different dating techniques imo. The 1,500 year ice age cycle is also relevant as well as the 100,000 year inclination cycle and would indicate that this is a cycle within the Sun's innermost core imo.

    Attached Files:

    Last edited: Aug 29, 2010
  9. Aug 28, 2010 #8
    Indeed there is a ~200 years challenge to solve in late Pleistocene dating, especially the start of the Younger Dryas. Was this around 12.9 Ka Cal BP (12900 calendar years before present) or 12.7 ka Cal BP?

    But the discrepancy here appears to be mainly deviation in annual layer counting, when comparing for instance the GRIP and GISP-II ice core data.
  10. Aug 28, 2010 #9


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    Screw that, everything we know about nuclear and particle physics would need revision.

    But the short of it is, nobody believes this claim.
  11. Aug 29, 2010 #10
    I thought science was about falsifying rather than not-believing.
    Last edited: Aug 29, 2010
  12. Aug 29, 2010 #11
    Good point, although your implied statement "nobody believes this claim" isn't even close to the tone of the Discover article. Why would you say that for? You sound particularly biased against a 'new physics'? Are you are mathematician by any chance?
    This is the tone of the article imv.
    Last edited: Aug 29, 2010
  13. Aug 29, 2010 #12
    You're right Andre of course. Here's an interesting article which made some predictions about the nature of neutrinos Where Cosmology and Particle Physics Meet
    The Discover article said:
    This happens to resonate well with my personal model due to inner core tidal bulges producing energy waves which would propogate to the Sun's surface, producing flares. I can even go further now and speculate that neutrinos are of a helical form and hence a force carrier for innermost exotic core matter. Maybe this is going to be a little too much to get your head around just yet though..
    Last edited: Aug 29, 2010
  14. Aug 29, 2010 #13
    I think, it's a bit early for speculations. Actually when somebody is reporting variation in half values of unstable isotopes, we have a verifiable claim there, I'd first wait for scrutinizing audits of their hardware, methods, observations and see if it can be reproduced. Then I'd design my own alternate experiment measuring different half times of different isotopes and see if the results concur.

    If so, only then it's time to look around and see if there is another signal corrollating with the variation.
  15. Aug 30, 2010 #14
    You sound as if you have your own lab and financial backing Andre! I'm a penniless thinker who likes to speculate about not only bending the well-established 'laws' of physics but produce an entirely new picture from scratch. I think I need to start a new thread entitled 'Where Cosmology Meets Particle Physics' or something similar. The carbon dating issue is an interesting one, but as alxm says, it's currently small fry compared to the 'new physics' angle. Best of luck Andre.
  16. Aug 30, 2010 #15
  17. Sep 3, 2010 #16


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  18. Sep 3, 2010 #17
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