Join the Unexplained Mysteries community today! It's free and setting up an account only takes a moment.
- Sign In or Create Account -
Sign in to follow this  
Followers 2
Riaan

A radiocarbon dating question

116 posts in this topic

I hope that one of you will be able to explain the following.

As I understand, RC dating depends on the environmental conditions that existed during the life of a plant, and specifically the ratio of C14/C12 isotopes found in the plant. When the plant dies, the C14 starts decaying, while the C12 content remains unchanged. What I do not understand is why the calibrated RC dates diverge increasingly with age.

For example: a plant grew for a couple of days in a specific environment and died 1 000 years ago. The same plant had grown and died under identical conditions 10 000 years ago. The C14/C12 ratio of both plants at the time of death should therefore be identical. The only difference in the RC dates should then be 9 000 years as determined by the C14 rate of decay. No correction should be required (is this assumption wrong?). However, the difference between the calibrated dates is nearly 10 500 years.

I am sure it is simply due to my lack of understanding about how the process works.

1 person likes this

Share this post


Link to post
Share on other sites

The source of the C12 and C14 for plants is the atmospheric CO2 that they absorb via photosynthesis. The ratio of C12 and C14 in the atmosphere has and does fluctuate with time, and thus two plant specimens of the same species in the same locale but separated by a thousand or more years can indeed have a different C12/C14 ratio at the time of death. The C12/C14 ratio has been recorded naturally such as in tree rings and certain mineral deposits, so we can sort of adjust or calibrate findings base on this record.

Share this post


Link to post
Share on other sites

Posted (edited)

I hope that one of you will be able to explain the following.

As I understand, RC dating depends on the environmental conditions that existed during the life of a plant, and specifically the ratio of C14/C12 isotopes found in the plant. When the plant dies, the C14 starts decaying, while the C12 content remains unchanged. What I do not understand is why the calibrated RC dates diverge increasingly with age.

For example: a plant grew for a couple of days in a specific environment and died 1 000 years ago. The same plant had grown and died under identical conditions 10 000 years ago. The C14/C12 ratio of both plants at the time of death should therefore be identical. The only difference in the RC dates should then be 9 000 years as determined by the C14 rate of decay. No correction should be required (is this assumption wrong?). However, the difference between the calibrated dates is nearly 10 500 years.

I am sure it is simply due to my lack of understanding about how the process works.

C14 is not a "natural" element, it is nitrogen that has been bombarded with cosmic rays, by which it acquired 2 extra neutrons and suddenly chemically works exactly as if it would be carbon. That is called a isotope (or "a element similar to"). These isotopes are not stable and will, sooner or later, loose those two neutrons again, and it is again nitrogen that reacts like nitrogen.

There are variation in the C14 concentration of the earth, that to start with, therefore it is necessary to use calibration equivalents, normally sourced from dateable strata such as layers of lakes.

As for the medium life, the isotopes decay continuously. It is not like suddenly half the isotopes disappear suddenly after 5,500 years. If you put a Geiger counter to anything radioactive every time it clicks a isotope has just decayed. It is just that statistically after 5500 years half of the C14 should be back to nitrogen. And, so far, within a percent or two it happens every time.

So, basically you are right, within a small variation the same organism will accumulate the same amount of carbon under same conditions, just, the longer the time, less of it will still be in the remains.

Edited by questionmark
1 person likes this

Share this post


Link to post
Share on other sites

The source of the C12 and C14 for plants is the atmospheric CO2 that they absorb via photosynthesis. The ratio of C12 and C14 in the atmosphere has and does fluctuate with time, and thus two plant specimens of the same species in the same locale but separated by a thousand or more years can indeed have a different C12/C14 ratio at the time of death. The C12/C14 ratio has been recorded naturally such as in tree rings and certain mineral deposits, so we can sort of adjust or calibrate findings base on this record.

My question is this: assuming that they had absolutely identical C12/C14 ratios at death (the environmental conditions just happened to be identical), but died 9 000 years apart, calibrated RC dating would place their deaths 10 500 years apart. Can't figure out what I am missing here.

Share this post


Link to post
Share on other sites

My question is this: assuming that they had absolutely identical C12/C14 ratios at death (the environmental conditions just happened to be identical), but died 9 000 years apart, calibrated RC dating would place their deaths 10 500 years apart. Can't figure out what I am missing here.

That is quite simple, if it is 9000 years apart the older sample will have only 1/4 (giver or take a little) of the C14 ratio the younger sample has, because the C14 of the older sample had a longer time to reconvert to nitrogen.

Once the organism is dead is accumulates no more carbon and therefore no more carbon 14.

1 person likes this

Share this post


Link to post
Share on other sites

That is quite simple, if it is 9000 years apart the older sample will have only 1/4 (giver or take a little) of the C14 ratio the younger sample has, because the C14 of the older sample had a longer time to reconvert to nitrogen.

Once the organism is dead is accumulates no more carbon and therefore no more carbon 14.

I am having trouble explaining myself, it seems. I assume that when an organism dies, its carbon composition is frozen. The C14 isotopes then start decaying and from this decay, which can be measured (this may be where I am going wrong), the age of organism can be calculated. Let's say the carbon reservoir and carbon absorption of a plant is constant and has never changed throughout history - will there be a need for calibration? One would simply determine the C14 decay and calculate the age of the organism. In my hypothetical example I assume this to have been the case at those two moments in time. To me it looks like RC calibration makes no provision for this example.

Share this post


Link to post
Share on other sites

I am having trouble explaining myself, it seems. I assume that when an organism dies, its carbon composition is frozen. The C14 isotopes then start decaying and from this decay, which can be measured (this may be where I am going wrong), the age of organism can be calculated. Let's say the carbon reservoir and carbon absorption of a plant is constant and has never changed throughout history - will there be a need for calibration? One would simply determine the C14 decay and calculate the age of the organism. In my hypothetical example I assume this to have been the case at those two moments in time. To me it looks like RC calibration makes no provision for this example.

But C14, as I tried to explain to you above (and a few others a dozen times) IS NOT CARBON, it is nitrogen that acquired two extra neutrons through cosmic radiation and therefore NOT STABLE, it will decompose sooner or later, whether the organism is alive or dead, capiche? If the organism is alive it will accumulate new C14 for the decomposed, while if it is dead it cannot accumulate any carbon anymore and therefore no C14 either.

Share this post


Link to post
Share on other sites

But C14, as I tried to explain to you above (and a few others a dozen times) IS NOT CARBON, it is nitrogen that acquired two extra neutrons through cosmic radiation and therefore NOT STABLE, it will decompose sooner or later, whether the organism is alive or dead, capiche? If the organism is alive it will accumulate new C14 for the decomposed, while if it is dead it cannot accumulate any carbon anymore and therefore no C14 either.

My mistake - could someone please fix the Wikipedia article on radiocarbon dating? Should it rather be called nitrogen dating? Of course it is not stable. Given the same starting point, the rate of decay of the two samples will be constant along an exponential curve. This rate of decay will presumably no longer be affected by the external environment, as the plant no longer absorbs any carbon/nitrogen from its surroundings (is this true?). The raw RC date will then reflect the exact time difference of 9000 years, because of the fact that the two samples had the same starting date and that the only change in the C12/C14 ratio is due to the C14 decay. Calibration of this date would in my opinion be incorrect.

Share this post


Link to post
Share on other sites

My mistake - could someone please fix the Wikipedia article on radiocarbon dating? Should it rather be called nitrogen dating? Of course it is not stable. Given the same starting point, the rate of decay of the two samples will be constant along an exponential curve. This rate of decay will presumably no longer be affected by the external environment, as the plant no longer absorbs any carbon/nitrogen from its surroundings (is this true?). The raw RC date will then reflect the exact time difference of 9000 years, because of the fact that the two samples had the same starting date and that the only change in the C12/C14 ratio is due to the C14 decay. Calibration of this date would in my opinion be incorrect.

Basically yes, as soon as an animal/plant dies it no longer uses carbon as combustible and whatever it has in it at that point in time is what will be found in its remains.

Calibration is more complicated than the ratio, because radiation varies. In fact at this point in time we have about 100% more C14 on the planet than there ever was before due to atomic testing. That is why I mentioned lakes above. Just like tree rings undisturbed lakes layer sediment of mineral and organic origin year after year. So to determine what is normal samples are taking from these layers and tested. To this point we have samples that go as far back as 40,000 years and therefore a good idea what the natural radiation incidence was until then. Taken that in consideration the measurements are corrected giving a date within a few percent of error.

Share this post


Link to post
Share on other sites

But C14, as I tried to explain to you above (and a few others a dozen times) IS NOT CARBON, it is nitrogen that acquired two extra neutrons through cosmic radiation and therefore NOT STABLE, it will decompose sooner or later, whether the organism is alive or dead, capiche? If the organism is alive it will accumulate new C14 for the decomposed, while if it is dead it cannot accumulate any carbon anymore and therefore no C14 either.

C14 is carbon.

You are correct that is it produced from nitrogen being struck by cosmic rays, and that it is not stable, but the nuclear equation is 147N + 10n --> 146C + 11p.

In short N14 gains a neutron, forming N15, then loses a proton becoming C14.

Share this post


Link to post
Share on other sites

C14 is carbon.

You are correct that is it produced from nitrogen being struck by cosmic rays, and that it is not stable, but the nuclear equation is 147N + 10n --> 146C + 11p.

In short N14 gains a neutron, forming N15, then loses a proton becoming C14.

If it was carbon it would stay carbon until radiated and acquiring neutrons to be something else, it does not, sooner or later it will loose those neutrons and is what it always was: nitrogen. It just assumed the role of carbon for some time (albeit between a second and a billion years). You can irradiate lead until it becomes a gold isotope, it still is not gold.

Share this post


Link to post
Share on other sites

Posted (edited)

Basically yes, as soon as an animal/plant dies it no longer uses carbon as combustible and whatever it has in it at that point in time is what will be found in its remains. ... Calibration is more complicated than the ratio, because radiation varies.

This is exactly what bothers me - here you refer to the radiation that varies. I assume you mean the radiation (C14) absorbed by the organism when it was still alive. In my hypothetical example the radiation and everything else is exactly the same for the two samples. If you meant a varying rate of decay in the organism, that is also the same in my example. In other words, the level of decay can be calculated accurately from the exponential curve, which is by definition the 'raw' RC date. If you now apply the calibration curve, you get a totally incorrect answer.

On calibration - the need for calibration arose because of the variation in the level of C14 in the atmosphere. I am reasonably familiar with the processes followed for the creating the calibration curves (as you refer to). However, the calibration curves do not seem to make provision for my hypothetical case, which could actually occur. I really don't know what to think. Do you agree that if you have the same starting point (C12/C14 ratio, etc), calibration cannot be done? If not, why not?

PS: Nearly midnight in South Africa, will check again tomorrow.

Edited by Riaan

Share this post


Link to post
Share on other sites

This is exactly what bothers me - here you refer to the radiation that varies. I assume you mean the radiation (C14) absorbed by the organism when it was still alive. In my hypothetical example the radiation and everything else is exactly the same for the two samples. If you meant a varying rate of decay in the organism, that is also the same in my example. In other words, the level of decay can be calculated accurately from the exponential curve, which is by definition the 'raw' RC date. If you now apply the calibration curve, you get a totally incorrect answer.

On calibration - the need for calibration arose because of the variation in the level of C14 in the atmosphere. I am reasonably familiar with the processes followed for the creating the calibration curves (as you refer to). However, the calibration curves do not seem to make provision for my hypothetical case, which could actually occur. I really don't know what to think. Do you agree that if you have the same starting point (C12/C14 ratio, etc), calibration cannot be done? If not, why not?

PS: Nearly midnight in South Africa, will check again tomorrow.

yes, and one died 9000 years before the other (or almost twice the half life), therefore there should be about 1/4 of the C14 as found in the younger sample. And that is how you measure the age of the sample.

Share this post


Link to post
Share on other sites

But C14, as I tried to explain to you above (and a few others a dozen times) IS NOT CARBON, it is nitrogen that acquired two extra neutrons through cosmic radiation and therefore NOT STABLE, it will decompose sooner or later, whether the organism is alive or dead, capiche? If the organism is alive it will accumulate new C14 for the decomposed, while if it is dead it cannot accumulate any carbon anymore and therefore no C14 either.

QM - With all due respect, and as Insanity pointed out, 14C (and 13C) are both isotopes of 12C. From a metabolic perspective, lifeforms utilize 14C in the same manner(s) as 12C, hence their incorporation. Due to the metabolic incorporation aspect, induced 14C is utilized as a marker in current medical research.

While the isotope 14C does decay to 14N, prior to decay it is considered to be a carbon.

.

2 people like this

Share this post


Link to post
Share on other sites

This is exactly what bothers me - here you refer to the radiation that varies. I assume you mean the radiation (C14) absorbed by the organism when it was still alive. In my hypothetical example the radiation and everything else is exactly the same for the two samples. If you meant a varying rate of decay in the organism, that is also the same in my example. In other words, the level of decay can be calculated accurately from the exponential curve, which is by definition the 'raw' RC date. If you now apply the calibration curve, you get a totally incorrect answer.

On calibration - the need for calibration arose because of the variation in the level of C14 in the atmosphere. I am reasonably familiar with the processes followed for the creating the calibration curves (as you refer to). However, the calibration curves do not seem to make provision for my hypothetical case, which could actually occur. I really don't know what to think. Do you agree that if you have the same starting point (C12/C14 ratio, etc), calibration cannot be done? If not, why not?

PS: Nearly midnight in South Africa, will check again tomorrow.

Actually, they do. The calibration curves are based upon proxies that reflect the variations in atmospheric 14C. If you choose to run the IntCal or OxCal programs on a series of dates, you will find that the spread of the intercepts can vary depending upon the atmospheric 14C of a given period. However, you will generally find that as your raw data begins to exceed circa 3-4 kya, the disparity between the raw data and the calibrated date will increase. In the case of disparities, the calibrated dates will generally be earlier than the raw data.

.

Share this post


Link to post
Share on other sites

I am having trouble explaining myself, it seems. I assume that when an organism dies, its carbon composition is frozen. The C14 isotopes then start decaying and from this decay, which can be measured (this may be where I am going wrong), the age of organism can be calculated. Let's say the carbon reservoir and carbon absorption of a plant is constant and has never changed throughout history - will there be a need for calibration? One would simply determine the C14 decay and calculate the age of the organism. In my hypothetical example I assume this to have been the case at those two moments in time. To me it looks like RC calibration makes no provision for this example.

A plant that lived 9,000 years previous to another plant might have more (or less) C14 than its counterpart because during the older plants life, there was more (or less) C14 in the atmosphere than there was during the younger plant's life.

Harte

Share this post


Link to post
Share on other sites

Posted (edited)

QM - With all due respect, and as Insanity pointed out, 14C (and 13C) are both isotopes of 12C. From a metabolic perspective, lifeforms utilize 14C in the same manner(s) as 12C, hence their incorporation. Due to the metabolic incorporation aspect, induced 14C is utilized as a marker in current medical research.

While the isotope 14C does decay to 14N, prior to decay it is considered to be a carbon.

.

Chemically until it decays it is a carbon like isotope, not carbon. And because most people don't get that they have problems with understanding carbon dating.

Edited by questionmark

Share this post


Link to post
Share on other sites

A plant that lived 9,000 years previous to another plant might have more (or less) C14 than its counterpart because during the older plants life, there was more (or less) C14 in the atmosphere than there was during the younger plant's life.

Harte

Hi Harte,

Perhaps my formulation of the problem is incorrect - would it have been possible for the atmospheric conditions to be the identical 9000 years apart? If so, calibration of the data presents a problem. If not, calibration will be required.

I am assuming that the rate of C14 decay is fixed (exponential) and is not influenced by any other external factors during the process of decay up to the point where we modern human beings analyze it. The number of C14 atoms N(t) is described by N0 e-gt, where g is the decay constant, g=ln(2)/5730, and t=time in years. If N0 was the same 10000 and 1000 years ago, respectively, as I postulate in my example, then this simple equation should predict a difference of exactly 9000 years. If you calibrate these dates, the difference becomes 10500 years. How is this possible, unless N0 was different at these two points in time?

Share this post


Link to post
Share on other sites

Hi Harte,

Perhaps my formulation of the problem is incorrect - would it have been possible for the atmospheric conditions to be the identical 9000 years apart? If so, calibration of the data presents a problem. If not, calibration will be required.

I am assuming that the rate of C14 decay is fixed (exponential) and is not influenced by any other external factors during the process of decay up to the point where we modern human beings analyze it. The number of C14 atoms N(t) is described by N0 e-gt, where g is the decay constant, g=ln(2)/5730, and t=time in years. If N0 was the same 10000 and 1000 years ago, respectively, as I postulate in my example, then this simple equation should predict a difference of exactly 9000 years. If you calibrate these dates, the difference becomes 10500 years. How is this possible, unless N0 was different at these two points in time?

Because in those 9000 years there could have been a flare of solar activity, therefore more cosmic radiation and with that more C14, just as an example.

Share this post


Link to post
Share on other sites

Because in those 9000 years there could have been a flare of solar activity, therefore more cosmic radiation and with that more C14, just as an example.

I am not disputing that N0 could have been different, as for example due to your flare of solar activity. However, in my example I assume that there was a modern scientist who recorded the atmospheric conditions exactly 10 000 years ago, and another who did the same 1 000 years ago, and N0 turned out to be exactly the same in both cases. It is certainly a possibility that this could have happened in reality, I would think. If so, C14 decay gives a difference of 9000 years, while the calibrated difference is 10500 years.

Share this post


Link to post
Share on other sites

Posted (edited)

Hi Harte,

Perhaps my formulation of the problem is incorrect - would it have been possible for the atmospheric conditions to be the identical 9000 years apart? If so, calibration of the data presents a problem. If not, calibration will be required.

I am assuming that the rate of C14 decay is fixed (exponential) and is not influenced by any other external factors during the process of decay up to the point where we modern human beings analyze it. The number of C14 atoms N(t) is described by N0 e-gt, where g is the decay constant, g=ln(2)/5730, and t=time in years. If N0 was the same 10000 and 1000 years ago, respectively, as I postulate in my example, then this simple equation should predict a difference of exactly 9000 years. If you calibrate these dates, the difference becomes 10500 years. How is this possible, unless N0 was different at these two points in time?

Possible, yes. But evidenced, then no:

A series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed 14C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Mono Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

http://courses.washi...-50ka_Sci04.pdf

cormac

Edited by cormac mac airt

Share this post


Link to post
Share on other sites

Posted (edited)

I am not disputing that N0 could have been different, as for example due to your flare of solar activity. However, in my example I assume that there was a modern scientist who recorded the atmospheric conditions exactly 10 000 years ago, and another who did the same 1 000 years ago, and N0 turned out to be exactly the same in both cases. It is certainly a possibility that this could have happened in reality, I would think. If so, C14 decay gives a difference of 9000 years, while the calibrated difference is 10500 years.

Not so long ago I posted in the Archeology forum (and should still be there) the methods used to reconstruct the biological conditions of the past (including carbon ratios), one very popular is to collect samples out of the beds of ancient lakes, as seen here:

800px-Channel-StellartonFm-CoalburnPit.JPG

Every layer you see here represents a year in geological history, and every one has samples from which you can determine the abnormalities due to climate or solar activity. Before I forget it, every layer here is between 1/4 and 1" thick.

Edited by questionmark

Share this post


Link to post
Share on other sites

Chemically until it decays it is a carbon like isotope, not carbon. And because most people don't get that they have problems with understanding carbon dating.

That makes no sense. If it's still nitrogen, why don't they call it that? You're changing the atomic number so you're changing it into another element, how ever impermanently. It even has a very specific place on the nuclide table:

https://en.wikipedia.org/wiki/Table_of_nuclides_%28complete%29

If we accept your argument, then no isotopes or transuranics exist as discrete elements because they all decay into something else from the initial nuclear reaction that created them, the latter artificially.

It's a convenient way of thinking of it I suppose but it's not accurate.

Share this post


Link to post
Share on other sites

That makes no sense. If it's still nitrogen, why don't they call it that? You're changing the atomic number so you're changing it into another element, how ever impermanently. It even has a very specific place on the nuclide table:

https://en.wikipedia...ides_(complete)

If we accept your argument, then no isotopes or transuranics exist as discrete elements because they all decay into something else from the initial nuclear reaction that created them, the latter artificially.

It's a convenient way of thinking of it I suppose but it's not accurate.

As long as they decay they are what they decay into, being bombarded by neutrons and by that changing molecular bounding properties is an aberration of the natural state, not a new state.

Let me simplify that: Even dressed in silk a monkey remains a monkey.

Share this post


Link to post
Share on other sites

Possible, yes. But evidenced, then no:

http://courses.washi...-50ka_Sci04.pdf

cormac

Thanks, a very useful reference. You may remember the reason behind all my questions - in my book Thera and the Exodus I, link many others, link the biblical plagues of Egypt and the Exodus to an eruption of Thera. I show that that the eruption must have occurred during the reign of Amenhotep III, ca. 1360 BCE. However, this link is summarily rejected by scholars as the final eruption of Thera was dated to ca. 1613 BCE by the RC dating of an olive tree found in Thera's ash.

It is perhaps more than a coincidence that the uncalibrated RC date for the calibrated date of 1610 BCE is 1364 BCE, which is very close to my postulated date. Assuming that 1360 BCE was the actual year of the eruption, the result of the RC dating process of the olive tree would have shown a decay to 66.4% (1360 BCE is 3373 years ago, exp(-3373g)=0.664, N0=1). If, however, the eruption occurred in 1613 BCE (3626 years ago), what value of N0 would give the same level of decay? The answer is N0 = 0.664/exp(-3626g) = 1.031. In other words, a 3% change in N0 results in a 253 year difference, for the same level of decay. How accurately can scientists predict the C14 content of the atmosphere that long ago?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 2

  • Recently Browsing   0 members

    No registered users viewing this page.