What is the most accurate half time for carbon dating?

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In summary, the first half time of radioactive carbon (14C) that got some consensus is the Libby date of 5568 years, which is still used. However, a more accurate half-life of 5730±40 years has been determined, known as the Cambridge half-life. A possible explanation for discrepancies in carbon dating results and atmospheric concentrations of radiocarbon is an underestimation of the 14C half-life. A recalculated half-life of 6030 years has been proposed as a more suitable estimate. The variation in 14C ratio is also influenced by cosmic radioactivity and the Earth's magnetic field. Further research and accurate measurements of the 14C half-life are needed for radiocarbon-based studies.
  • #1
Andre
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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

Carbon dating was developed by a team led by Willard Libby. Originally a Carbon-14 half-life of 5568±30 years was used, which is now known as the Libby half-life. Later a more accurate figure of 5730±40 years was determined, which is known as the Cambridge half-life. However laboratories continue to use the Libby figure to avoid inconsistencies when comparing raw dates and when using calibration curves to obtain calendrical dates.

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:

http://radiocarbon.ldeo.columbia.edu/pubs/2006Chiu.pdf

An under-estimate of the 14C half-life is a possible explanation for excessively elevated Δ14C values. If the calorimetry estimated 14C half-life, 6030 years, is validated by new half-life measurements, it could explain much of the linear component of the radiocarbon calibration curves and the discrepancy between Δ14C values derived from corals and modeled Δ14C values based on paleointensity combined with a range of carbon cycle scenarios. We conclude that the variation in paleointensity and a possible offset in the absolute value of 14C half-life together control the overall shape and amplitude in the Δ14C record for the past 50,000 years.

A re-determination of the 14C half-life is urgently needed for radiocarbon-based research. After the 14C half-life is accurately measured and eplicated by multiple techniques, our coral data will provide an opportunity to examine subtler carbon cycle influences on the younger half of the Δ14C record.

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.
 
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  • #2
Well one can certainly call into question the half-life of any radionuclide, but then one should have evidence to support one's contention.

Radio-carbon dating is a method of obtaining age estimates on organic materials. The word "estimates" is used because there is a significant amount of uncertainty in these measurements. Each sample type has specific problems associated with its use for dating purposes, including contamination and special environmental effects. More information on the sources of error in carbon dating are presented at the bottom of this page.
http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/carbondating.htm

Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

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?
 
  • #3
Astronuc said:
Well one can certainly call into question the half-life of any radionuclide, but then one should have evidence to support one's contention.

Well, http://home.wanadoo.nl/bijkerk/d14C.GIF [Broken]. (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 disappear if the half value of 14C was to be 6030 years instead of 5730 years.

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?

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.

http://home.wanadoo.nl/bijkerk/d14C-d18O.GIF [Broken] 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.
 
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  • #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.
 
  • #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?
 
  • #6
Reviving this thread because of this News release of Stanford. It's now hypothesed that neutrinos could affect half life of unstable isotopes.

"It's an effect that no one yet understands," agreed Sturrock. "Theorists are starting to say, 'What's going on?' But that's what the evidence points to. It's a challenge for the physicists and a challenge for the solar people too."

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 http://radiocarbon.ldeo.columbia.edu/pubs/2006Chiu.pdf. Could it be that all of them were right at the time?
 
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  • #7
Andre said:
Reviving this thread because of this News release of Stanford. It's now hypothesed that neutrinos 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 http://radiocarbon.ldeo.columbia.edu/pubs/2006Chiu.pdf. Could it be that all of them were right at the time?
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 http://www.maths.qmul.ac.uk/~lms/research/neutrino.html [Broken]. 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.
 

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  • #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 ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/grip/isotopes/gripd18o.txt and ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gispd18o.txt ice core data.
 
  • #9
Andre said:
Just about everything that relies on isotope dating techniques may need revision.

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

But the short of it is, http://blogs.discovermagazine.com/80beats/2010/08/26/scientist-smackdown-are-solar-neutrinos-messing-with-matter/" [Broken]
 
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  • #10
I thought science was about falsifying rather than not-believing.
 
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  • #11
alxm said:
Screw that, everything we know about nuclear and particle physics would need revision.

But the short of it is, http://blogs.discovermagazine.com/80beats/2010/08/26/scientist-smackdown-are-solar-neutrinos-messing-with-matter/" [Broken]
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?
“Data is data. That’s the final arbiter. But the more one has to bend [well-establish physics], the evidence has to be that much more scrutinized.”
This is the tone of the article imv.
 
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  • #12
Andre said:
I thought science was about falsifying rather than not-believing.
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
Of all the scattered pieces of physics that the TeV scale will serve to illuminate, neutrino physics is one of the most remarkable — not least because it shows up in so many different contexts. The recent discovery that neutrinos have mass is particularly significant for "vertical" questions like whether and how the forces of nature may be aspects of the same force... Neutrino mass and neutrino oscillations may be a key to grand unified theories, theories that regard the electromagnetic, weak, and strong forces as aspects of a single kind of interaction. The still-mysterious nature of neutrinos may even hold the answer to the origin of all matter in the universe.
(See diagram) If neutrinos and antineutrinos are the same particle, when an ordinary neutrino (blue) collides with a Higgs boson, it transforms into a short-lived, very massive antineutrino (red), which soon converts back to an ordinary neutrino. This so-called seesaw mechanism may mean that neutrinos and antineutrinos are the ultimate source of all matter in the universe.
The Discover article said:
The Purdue-Stanford team cites an example of a 2006 solar flare, saying that they saw a dip in decay rates in a manganese isotope before the occurrence that lasted until after it was gone. Sullivan, however, says he isn’t convinced this is experimentally significant, and anyway it doesn’t make sense: Solar neutrinos emanate from the interior of the sun—not the surface, where flares emerge. Moreover, he says, other solar events like x-ray flares didn’t have the same effect...
And in response to number two—why would you tie neutrinos to a flare, when they emanate from the sun’s interior?—Jenkins and Fischbach write that we know some flares are tied to events deep inside the sun. “We therefore consider it possible that events in the core may influence flares,” they write, “but this remains to be established. We have never claimed that all flares are related to events in the core.”
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..
 
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  • #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.
 
  • #14
Andre said:
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.
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

What is carbon dating?

Carbon dating is a scientific method used to determine the age of organic materials by measuring the amount of carbon-14 present in the sample. This is based on the fact that carbon-14 is constantly formed in the Earth's atmosphere and is absorbed by living organisms. When an organism dies, the amount of carbon-14 decreases over time through radioactive decay, making it possible to estimate how long ago the organism died.

How does carbon dating work?

Carbon dating works by measuring the ratio of carbon-14 to carbon-12 in a sample, which is then compared to the known ratio in living organisms. The rate of carbon-14 decay is constant, so by measuring the amount of carbon-14 remaining in a sample, scientists can calculate how long it has been since the organism died.

What is the half-life of carbon-14?

The half-life of carbon-14 is approximately 5,730 years. This means that it takes 5,730 years for half of the carbon-14 in a sample to decay into nitrogen-14. This is an important factor in carbon dating, as it allows scientists to accurately determine the age of a sample by measuring the amount of carbon-14 remaining.

What are the limitations of carbon dating?

Carbon dating is limited to samples that contain organic materials, such as wood, bone, and cloth. It is also only accurate up to about 50,000 years, as after this time the amount of carbon-14 remaining in a sample is too small to be measured accurately. Additionally, external factors such as contamination or environmental changes can affect the accuracy of carbon dating results.

How is carbon dating used in archaeology?

Carbon dating is commonly used in archaeology to determine the age of artifacts and fossils. By dating organic materials found at a particular site, archaeologists can establish a timeline of when the site was occupied and gain insights into the lives of the people who lived there. Carbon dating has been a crucial tool in helping archaeologists understand human history and cultural development over time.

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