Help Calibrate C-14

[grace24]

I have spent a few weeks studying how C-14 work and things of that nature, but i get confused when scientists uses C-14 to calibrate tree rings of that sort. C-14 only last to about 40,000 years or so, and it is not the only method they use. To date older things such as rocks etc. they use other methods such as uranium-lead.

So... How do they calibrate C-14 with tree rings? How do they compare dates with each other?

 

[shernren]

The best tree-ring chronologies go back about 26,000 years:

Dendrochronology - Wikipedia, the free encyclopedia

so even the oldest tree-rings are well within the range of C14.

 

[Assyrian]

I have spent a few weeks studying how C-14 work and things of that nature, but i get confused when scientists uses C-14 to calibrate tree rings of that sort. C-14 only last to about 40,000 years or so, and it is not the only method they use. To date older things such as rocks etc. they use other methods such as uranium-lead.

So... How do they calibrate C-14 with tree rings? How do they compare dates with each other?

Carbon dating, as you probably realise, depends on the amount of Carbon 14 in the atmosphere back in the past when the sample was alive, the level varied with cosmic ray intensity, fluctuations in the earth's magnetic field and even ocean circulation. While it didn't vary that much, it varies enough over to distort carbon dating readings. With dendrochronology you can have an absolute reading of the age of, say, a timber beam found in an archaeological site. Take a Carbon 14 read on the wood and instead of being say 2,800 years old from dendrochronology, radio carbon dating says 2,600. That means if you go to another site and the radiocarbon says '2,600' years old, you know from dendrochronology that this means it is really 2,800 years old. What they have actually done is produce a graph of all the dendrochronology dates compared to C14 readings for the same sample. Then you can read off any uncalibrated C14 reading against the real date.

Check out the graph in Radiocarbon dating - Wikipedia, the free encyclopedia



For older dates, layers of sediment in lakes called varves can be used.
Have a look at Glenn Morton's page on radiocarbon dating and lake suigetsu

 

[philadiddle]

Here is a highly technical paper on the calibration curved for C14 dating that goes back about 26,000 years. It has an error margin of about ±163 years over the entire 26,000 years of the curve. For the first 6,000 years the margin of error is only about ±16 years.

http://digitalcommons.library.arizo...umber3/azu_radiocarbon_v46_n3_1029_1058_v.pdf

 

[grace24]

Take a Carbon 14 read on the wood and instead of being say 2,800 years old from dendrochronology, radio carbon dating says 2,600.

I'm lost here. Just to clarify, so it's not the 2,800. We'll go with 2,600 that C-14 read from the wood instead, right?

That means if you go to another site and the radiocarbon says '2,600' years old, you know from dendrochronology that this means it is really 2,800 years old.

I'm lost here again. I might be too slow, sorry. So you go to another site (along with C-14 we just read from the wood to be 2,600), how does that connect to dendrochronology that this mean it is really 2,800 years old? How does 2,600 simply change into 2,800 now? I thought the wood was 2,600?

 

[philadiddle]

I'm lost here. Just to clarify, so it's not the 2,800. We'll go with 2,600 that C-14 read from the wood instead, right?

It's the other way around. We go from the wood and adjust the C14 reading to that. Tree rings are very reliable, but the C14 ratio in the atmosphere changes over time, so we adjust for that by comparing C14 to dating methods that are more accurate to calibrate it. That makes C14 dating just as accurate.

I'm lost here again. I might be too slow, sorry. So you go to another site (along with C-14 we just read from the wood to be 2,600), how does that connect to dendrochronology that this mean it is really 2,800 years old? How does 2,600 simply change into 2,800 now? I thought the wood was 2,600?

So if we get a simple C14 reading of 2,600 years, then we know from the comparison we made to dendrochronology in the example above that that is actually 2,800 years old.

To explain it a different way think of this; We have a piece of wood that we can date by both dendrochronology and C14 dating. We know that dendrochonology is accurate to the year and we know that C14 dating will be close, but there will be a margin of error. So when the tree ring dating method gives us an age of 2,800 years we know that that is accurate to the year. If the C14 method gives us 2,600 years we know that it is close but not perfect. Since, in this example, we have the ability to compare C14 dating to dendrochronology then we can adjust the reading up to 2,800 years. Now we know that if something reads 2,600 years it is actually 2,800 years old. So now when we don't have another dating method at our disposal, and all we can use is C14 dating, if we get an age of 2,600 years with a straight line method we know we can adjust it up to 2,800 years because of the other example.

(Note: the numbers used are ficticious, I don't think you actually have to adjust it by that many years but that's besides the point.)

 

[grace24]

It's the other way around. We go from the wood and adjust the C14 reading to that. Tree rings are very reliable, but the C14 ratio in the atmosphere changes over time, so we adjust for that by comparing C14 to dating methods that are more accurate to calibrate it. That makes C14 dating just as accurate.

So suppose the wood is 2,800, we go from here and adjust the C-14 reading to the wood? The C-14 here comes from the other sample, right? So if this sample of C-14, say 2,600, and if we get 2,800 from the wood, so this makes C-14 2,800? So actually all we did was change 2,800 from the wood and use that age for the C-14 sample.

 

[philadiddle]

So suppose the wood is 2,800, we go from here and adjust the C-14 reading to the wood? The C-14 here comes from the other sample, right? So if this sample of C-14, say 2,600, and if we get 2,800 from the wood, so this makes C-14 2,800? So actually all we did was change 2,800 from the wood and use that age for the C-14 sample.

I'm sorry but these questions are confusing. I'm not sure what you're asking.

 

[Sophophile]

So suppose the wood is 2,800, we go from here and adjust the C-14 reading to the wood? The C-14 here comes from the other sample, right? So if this sample of C-14, say 2,600, and if we get 2,800 from the wood, so this makes C-14 2,800? So actually all we did was change 2,800 from the wood and use that age for the C-14 sample.

Hi Grace

Maybe I can help simplify this.

Tree ring dating gives us exact years - one ring equals one year. So if we count 1003 rings, that means the tree is exactly 1003 years old.

On the other hand, measuring Carbon-14 doesn't give years at all. It just gives a percentage -- the percentage of C14 remaining.

We know C14 decays over time, and we know the rate of decay, but we don't have perfect information about the starting amount of C14. So we can guess the age of something from the percentage of C14 remaining, but it will only be a rough guess.

Now here's the interesting part: We can carbon-date trees. This means we can count the rings in a tree, and we can also carbon date the same tree. We can then compare the tree-ring count of exact years to the carbon dating guess, and see how far off the carbon-dating guess is.

It turns out if you do this procedure on thousands of tree samples, a pattern emerges: Look at the first graph in Assyrian's post above. The blue line is the C14 guess. The red line shows exact years counted from tree rings. This shows that carbon-dating guesses are too old, and the problem gets worse the older the tree is.

However, the C14 error is a systematic error. It follows a predictable pattern (and in fact we know the cause of this, which is related to the levels C14 in the atmosphere changing over time). This means that we can correct the C14 error, because we know very accurately what the error is for any particular time in the past. This process of correcting for a known error is called calibration.

Because we can calibrate the C14 dating process, we can use it reliably on samples other than trees.

Hope this helps!

S.

 

[grace24]

Now here's the interesting part: We can carbon-date trees. This means we can count the rings in a tree, and we can also carbon date the same tree. We can then compare the tree-ring count of exact years to the carbon dating guess, and see how far off the carbon-dating guess is.

Oh i see now. What i didn't know and confused about is that you have to carbon date the same tree you are counting. I thought you carbon date something different, then come back to a new tree and count the rings. But actually you count the same tree you are carbon dating in order to calibrate where the error are. Am i right?

Thanks for clarifying the chart to me. I knew i was confused. I might be wrong though, but on the chart the difference between the carbon dating and the tree rings is by 1000 years?

 

[Sophophile]

Oh i see now. What i didn't know and confused about is that you have to carbon date the same tree you are counting. I thought you carbon date something different, then come back to a new tree and count the rings. But actually you count the same tree you are carbon dating in order to calibrate where the error are. Am i right?

Yes, that's the idea.

I don't want to be misleading, however. The actual science is a little more complex. For example, it is not a single tree that is dated by tree-ring counting, but sequences of many trees whose tree-rings overlap.

Thanks for clarifying the chart to me. I knew i was confused. I might be wrong though, but on the chart the difference between the carbon dating and the tree rings is by 1000 years?

That's about right. But its important not to think of the carbon dates as "years" (i.e. the blue line). Scientists call them "radiocarbon years" because they know they do not represent actual calendar years before they have been calibrated.

The way this all works is simple. There is a tiny amount of the radioactive carbon isotope C14 throughout the atmosphere and ocean. The percentage of C14 stays roughly constant at 1 part per trillion. It stays constant because, on the one hand, C14 is constantly produced in the upper atmosphere by cosmic rays and, on the other hand, C14 undergoes radioactive decay and turns into (non-radioactive) Nitrogen-14, and the rate of production is in equilibrium with the rate of decay.

Now, all livings things are made of carbon and breathe/eat/live in water and air that contains carbon. Therefore, while alive, they contain the same percentage of C14 in their bodies as the atmosphere and the ocean - 1 part per trillion.

But when living things die, they stop exchanging carbon with their environment -- no more carbon, and no more C14, enters their dead body from the environment. However, the C14 that was in their body at death continues to undergo radioactive decay. The rate of radioactive decay of C14 is well known - it takes 5,800 years for half of any given amount of C14 to decay into N14.

Therefore, if we find a dead organism, and we measure the C14 in its body at 0.5 parts per trillion, we know that is about half the amount of C14 that was in its body when it was alive. And since we know the half-life of C14 is 5,800 years, then we know the organism was last alive about 5,800 years ago.


Cheers
S.

 

[pastorkevin73]

If Carbon dating is as accurate is being presented, then how is it that one scientist can take a sample and date it then another scientist comes along does the same test and comes up with a completely different date. Or am I thinking of a different method of dating?

 

[laconicstudent]

If Carbon dating is as accurate is being presented, then how is it that one scientist can take a sample and date it then another scientist comes along does the same test and comes up with a completely different date. Or am I thinking of a different method of dating?

Can you please show us the study documenting this inconsistency of which you speak?

 

[philadiddle]

If Carbon dating is as accurate is being presented, then how is it that one scientist can take a sample and date it then another scientist comes along does the same test and comes up with a completely different date. Or am I thinking of a different method of dating?

What is your source for the inconsistency that you're claiming?

 

[pastorkevin73]

I honestly cannot remember where I heard or read this. I might even be wrong as to this method of dating (as I mention in my question: Or am I thinkg of a different method?). I'm not asking anyone to take my word for it, I just can't remember the reference I got this from. What I can remember is that there was a form of dating that wasn't accurate. If I am thinking of some other dating method perhaps one of you could point me in the right direction. However, I do have the question: Is is possible to get more than one date through carbon dating on the same sample if more than one person attempts to date?
BTW, I'm not trying to argue here, I an honestly seeking the correct answer on this matter. I don't want to use any information I have if it isn't true.
Thanks, ye all!

 

[Papias]

Pastorkevin wrote:

BTW, I'm not trying to argue here, I an honestly seeking the correct answer on this matter. I don't want to use any information I have if it isn't true.

Thanks, and that is clear. I'm sorry that these discussions can get heated at times, and greatly appreciate coming across someone honestly discussing this. I'll apologize in advance if I sound too forceful. I agree that regardless of where we each are, we don't want to use any false information.

I honestly cannot remember where I heard or read this.

I'm not asking anyone to take my word for it, I just can't remember the reference I got this from.

I'm not trying to be unfairly accusative to creationists, but have seen this repeatedly. Creationists will often mispresent data so as to make it sound like a dating method is inaccurate, when the data doesn't say that at all. Often by exaggerating simple variation (any method has some variation), or misrepresenting lower limits of detection. For instance, C14 testing on the shroud of Turin by several different scientists at labs around the world gave dates that varied between 1260 AD to 1390 AD. That's the simple noise of the experiment. (
Radiocarbon dating of the Shroud of Turin
) Someone trying to cast doubt on the method could say that those dates "are different", but they aren't different. They all say its from a 13th to 14th century time, and all rule out dates earlier or later. Also, creationists will sometimes just plain make stuff up.

I might even be wrong as to this method of dating (as I mention in my question: Or am I thinkg of a different method?).

What I can remember is that there was a form of dating that wasn't accurate. If I am thinking of some other dating method perhaps one of you could point me in the right direction.

Possible, but like I said, it's quite possible that C14 was simply misrepresented by a creationist. Often, creationists simply aren't aware there are other dating methods, and will lie about C14 by default when they are just out to cast date on all dating methods, since all the dating methods agree and rule out a literal reading of Genesis (including written historical records).

If it was another dating method, say, one that tests for things hundreds of millions of years old, one scientist may have mesured a date of 177 +/- 5 million years ago, while a second measured 180 +/- 6 million years ago, in which case a creationists may have howled "they gave dates that disagreed with each other by three million years!!!!!!", when in actuality, the measurements agreed within the expected variance. See how that works? The first date is actually "172 to 182", and the second is "174 to 186" - they overlap, and hence agree.

Since we can know which one the person you heard from was talking about, it doesn't matter.

However, I do have the question: Is is possible to get more than one date through carbon dating on the same sample if more than one person attempts to date?
Thanks, ye all!

In general, no. With literally hundreds of tests being done across the world every year, even a test that is 99.7% accurate will have some mistakes somewhere, sometimes. Often, disagreements found are quickly discovered to be due to obvious causes, like a mistake in calculating, or a mistake in sample preparation (contamination must be carefully guarded against) and so on. But, as I said, with thousands of tests done since the test started, and hundreds done every year, the test has been so repeatedly shown to be accurate that disputing it is like disputing that gasoline can burn.

Papias

http://www.nature.com/nature/journal/v337/n6208/abs/337611a0.html

 

[laconicstudent]

I honestly cannot remember where I heard or read this. I might even be wrong as to this method of dating (as I mention in my question: Or am I thinkg of a different method?). I'm not asking anyone to take my word for it, I just can't remember the reference I got this from. What I can remember is that there was a form of dating that wasn't accurate. If I am thinking of some other dating method perhaps one of you could point me in the right direction. However, I do have the question: Is is possible to get more than one date through carbon dating on the same sample if more than one person attempts to date?
BTW, I'm not trying to argue here, I an honestly seeking the correct answer on this matter. I don't want to use any information I have if it isn't true.
Thanks, ye all!

Nobody can ever remember the reference. Honestly, it is just one of those anecdotes from the internet that likely has no basis in reality.

 

[pastorkevin73]

Pastorkevin wrote:



Thanks, and that is clear. I'm sorry that these discussions can get heated at times, and greatly appreciate coming across someone honestly discussing this. I'll apologize in advance if I sound too forceful. I agree that regardless of where we each are, we don't want to use any false information.




I'm not trying to be unfairly accusative to creationists, but have seen this repeatedly. Creationists will often mispresent data so as to make it sound like a dating method is inaccurate, when the data doesn't say that at all. Often by exaggerating simple variation (any method has some variation), or misrepresenting lower limits of detection. For instance, C14 testing on the shroud of Turin by several different scientists at labs around the world gave dates that varied between 1260 AD to 1390 AD. That's the simple noise of the experiment. (
Radiocarbon dating of the Shroud of Turin
) Someone trying to cast doubt on the method could say that those dates "are different", but they aren't different. They all say its from a 13th to 14th century time, and all rule out dates earlier or later. Also, creationists will sometimes just plain make stuff up.



Possible, but like I said, it's quite possible that C14 was simply misrepresented by a creationist. Often, creationists simply aren't aware there are other dating methods, and will lie about C14 by default when they are just out to cast date on all dating methods, since all the dating methods agree and rule out a literal reading of Genesis (including written historical records).

If it was another dating method, say, one that tests for things hundreds of millions of years old, one scientist may have mesured a date of 177 +/- 5 million years ago, while a second measured 180 +/- 6 million years ago, in which case a creationists may have howled "they gave dates that disagreed with each other by three million years!!!!!!", when in actuality, the measurements agreed within the expected variance. See how that works? The first date is actually "172 to 182", and the second is "174 to 186" - they overlap, and hence agree.

Since we can know which one the person you heard from was talking about, it doesn't matter.



In general, no. With literally hundreds of tests being done across the world every year, even a test that is 99.7% accurate will have some mistakes somewhere, sometimes. Often, disagreements found are quickly discovered to be due to obvious causes, like a mistake in calculating, or a mistake in sample preparation (contamination must be carefully guarded against) and so on. But, as I said, with thousands of tests done since the test started, and hundreds done every year, the test has been so repeatedly shown to be accurate that disputing it is like disputing that gasoline can burn.

Papias

Thank you Papias. You have been of great help. Your answer for the overlap especially was helpful. Thank you. This is much clearer to me.

 

[Papias]

You're welcome! I'm glad to have been able to help.