Carbon Dating

[NavajoEverclear]

Well evidently carbon dating does work, but how? I know it measures date by the state of the decay of the nucleus of the carbon atom---- but wouldn't it be true that none of the carbon is new? I'm i don't know when all the carbon was created or surfaced or whatever, but i know i'm not made of new carbon. My body is made from eating food that ate food that ate food--- shouldn't the carbon i'm made of really be as old as anything ancient as found in dinosaurs? So you see what i'm saying-- i don't understand how you can tell the age of it if i know i'm also made of ancient atoms, how come i dont have a carbon dating of a bazillion years (well i haven't recently got my carbon analyzed in such a way but i know it shouldn't say i'm that old). Is there something about life that preserves the atom from decaying, so only when an organism dies and is not taken up as food for another that the decay has time to begin?

[Skye]

It's based on the decay of carbon-14 to carbon-12. Most of the Earth's carbon-14 is created when electromagnetic radiation from the sun hits the carbon in carbon dioxide within the atmosphere. This is then taken in by plants during photosynthesis and by animals when they eat plants. When an animal or plant dies, they stop taking in any more carbon of any kind, but the carbon-14 continues to decay to carbon-12, meaning the percentage of carbon-14 falls as time goes by.

[JaKiri]

(It's assumed that the amounts of C14 in each living creature as a proportion remains constant, due to the interaction with the constantly created stuff, and this level was constant for the last few thousand years)

[NavajoEverclear]

i guess that answers the question, i still dont understand exactly how an organism keeps it from decaying during its life (so we know it didn't start decay till the thing died, otherwise something being built out of carbon that constantly decays, the dating would show from the creation of the atom, which would go back a very long time before being made part of the one it is finally found in and not recycled back)

[VendingMenace]

i guess that answers the question, i still dont understand exactly how an organism keeps it from decaying during its life (so we know it didn't start decay till the thing died, otherwise something being built out of carbon that constantly decays, the dating would show from the creation of the atom, which would go back a very long time before being made part of the one it is finally found in and not recycled back)

 

Most certainly carbon is decaying inside of you while you are still alive. Carbon 14 does not stop decaying just becuase it is in your body. But you are constantly getting more carbon from nature. This carbon from nature is in a particular ratio, so you are always at this ratio, until you die. Lets see if i can explain this in more depth...

 

Well, the idea is this...

 

While you are alive, you constantly are taking in carbon (through breathing in CO and CO2, and eating things that have carbon in then, like plants and animals). As such, you are in equilibrium with nature, as far as the ratio of carbon 14/ carbon 12 is concerned. That is, as long as you are alive, since you are taking in carbon from nature, it is assmed that you will have the same carbon 14/12 ratio as is found in nature.

 

Once you die, however, you stop taking in carbon from nature. Thus, you never get back carbon 14. When the carbon 14 in your bady decays, you get no more. Thus, over time, the carbon 14/12 ratio in you body will decrease. By measuring this ratio we find in a corpse, the ration found in nature, and given the half-life for carbon 14, we can estimate how long ago you would have kicked the bucket.

 

I hope this makes sense. The key is that while you are alive, even though carbon is decaying in you, you are constantly getting more from the environment. Thus, you are in equilibruim with your environment. Since the ration of carbon 14/12 in the world has not really changed, as far as we know, you can be assumed to always have the same ratio of carbon 14/12 in your body...until you die. Then this ratio starts going down.

 

If I am not quite being clear, feel free to ask more questions, and i will endevor to try and answer them

[NavajoEverclear]

Thanks lots that clears everything up, i thought carbon dating was done by measuring how far broken down the nucleus of carbon was (being unstable with all the extra nuetrons), actually thats what my biology teacher told me. So what your saying is its not that, its the ratio of carbon in your body, not the state of each atom of it? That i understand.

[aman]

That all made me ponder the question, if you were raised on polar ice melt from 100,000 years ago for your entire life, would your bones show signifigant difference in carbon dating?

Just aman

[VendingMenace]

So what your saying is its not that, its the ratio of carbon in your body

 

exactly

 

cool, now to clear up a few other things, just for your own personal edification...

 

i thought carbon dating was done by measuring how far broken down the nucleus of carbon was

 

the way you phrase this, it makes it sound like the nucleaus goes through a gradual degridation process, much like your shoes. That is, your shoes just kinda slowly wear down until one day, you can't use them anymore. This, however, is not how nuclear decay works. Carbon is either carbon 14 or carbon 12. There are not stages between. So, in nuclear degredation, it is like you have a carbon 14 atom sitting around and then BAM!, it releases a particle and now it is carbon 12.

 

Yeah, so the point being, radioactive decay is a stepwise mechanism and not a gradual process.

 

That is why we have to look at the ratio of carbon. If we were to just look at an individual atom we would find that it is either carbon 14 or carbon 12. This would tell us nothing. But the ratio of these carbons DOES tell us something. But i think you have grasp that

 

Cool. Well, like i said, if you have any more questions, please don't hesitate to ask

[Skye]

That all made me ponder the question, if you were raised on polar ice melt from 100,000 years ago for your entire life, would your bones show signifigant difference in carbon dating?

 

If I understand you correctly, i.e. drinking the water from 100,000 year old ice, you wouldn't get alot of carbon from it, so it wouldn't really affect radiocarbon dating. On the other hand, I think it's possible that an organism living off oil that is buried underground could be dated as close to the age of the oil, because it's source of carbon would be the oil. Course the carbon-14 decays relatively fast so that alot of oil supplies wouldn't be accurately measured.

[aman]

Your right, H2O, stupid question cus it was getting late, I hate apologizing the next day.

A person tending peat fires for his entire life might seam older than he was since the CO2 would be higher in C12 ratio.

Just aman

[VendingMenace]

that is exactly correct. In fact, there was a lab at Lawrence Livermore National labs that was doing things along these lines. They were growing plants in C14 free/limited environments, then harvesting the plants and dating them (come on, i no us scientists have bad social lives, but PLANTS? you gotta stick to your own species, man) Anyways, the plants appeared to be much older than they actually were. It was kinda cool, though expected.

[aman]

I see it works for plants but I forgot there is no exchange of carbon from CO2 in the air to the body. I'll go back to taking my medication, sometimes my Mom said she could handle both of me being crazy but drew the line at both of me being stupid.

Just aman

[Skye]

At least you're both funny

[swansont]

Skye said in post #2 :

It's based on the decay of carbon-14 to carbon-12

 

Not quite. C-14 decays to N-14. It's a beta decay, so a neutron changes into a proton, and emits an electron and antineutrino.

 

For C-14 to decay to C-12, it would need to emit two neutrons. Neutron emission can happen for some nuclei, but that requires an large excess of neutrons, and doesn't happen in this case.

[Skye]

Sorry, my mistake.