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Author Topic: How does carbon dating work?  (Read 4047 times)

Paul Anderson

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How does carbon dating work?
« on: 08/06/2008 19:52:56 »
Paul Anderson  asked the Naked Scientists:

If a carbon atom is in existence at the beginning of the Earth and it spends some of itís time in a bacteria, then a fish, then a amphibious animal and then a land animal, then a tree, which is used for making railway sleepers, and then a sleeper is cut up to make a chair.

If the chair is lost in the bog and found many years later, how do they carbon date it, if the carbon has had such a history? Might not the carbon dating of the chair coincide with some time during which the carbon may have been a sleeper?

Regards,

Paul,  NZ

What do you think?


 

Offline RD

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How does carbon dating work?
« Reply #1 on: 08/06/2008 21:12:50 »
Carbon dating tells when the organism it came from stopped respiring: when it stopped exchanging gasses with the atmosphere, (i.e. died).

So the carbon date in your example would correspond to when the tree to make the sleeper was felled.

[The inclusion of a bog in your example complicates matters. Organic material from the bog could contaminate the artifact to give an incorrect carbon date, e.g. if you buried an Ikea chair in a ancient bog, contamination could give the modern chair an ancient carbon date]. 
« Last Edit: 08/06/2008 21:16:26 by RD »
 

Offline Madidus_Scientia

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How does carbon dating work?
« Reply #2 on: 09/06/2008 02:57:46 »
Cosmic rays from the sun will often collide with an atom in the atmosphere, causing a neutron to be released. When one of these neutrons collides with a nitrogen atom, (nitrogen-14; seven protons, seven neutrons) the nitrogen atom is turned into a carbon-14 atom (six protons, eight neutrons) and a hydrogen atom.
This carbon-14 atom will then combine with oxygen to form carbon dioxide, which is taken in by plants for photosythesis. Non-plant life either consumes the plants to take in c14, or consumes the animal that consumed the plant, etc.

So the ratio of carbon-14 to normal carbon-12 in the atmosphere and in living organisms remains pretty much constant. The carbon atoms in a living thing will decay but are always being replaced, so the ratio remains constant until the organism dies.

So by comparing the carbon-14 to carbon-12 ratio in a once living thing to something still living, the age can be determined reasonably accurately. This will only work up to about 60,000 years though, after that all of the c14 will have decayed and the true age cannot be determined.
 

Offline SquarishTriangle

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How does carbon dating work?
« Reply #3 on: 09/06/2008 06:43:28 »
Well it all starts when one carbon atom meets eyes with another, thinks about her day and night and before too long, works up the courage to leave in her letterbox words of love on a daisy-scented note...

(Oh, it never gets old...or does it?)
 

lyner

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How does carbon dating work?
« Reply #4 on: 09/06/2008 09:02:58 »
But they're only kids. One's 12 and the other is 14!
 

Offline Madidus_Scientia

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How does carbon dating work?
« Reply #5 on: 09/06/2008 09:59:55 »
...and they live happily ever after and have long and fruitful half-lives
 

paul.fr

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How does carbon dating work?
« Reply #6 on: 09/06/2008 10:42:18 »
i thought it ended in tragedy.
 

Offline SquarishTriangle

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How does carbon dating work?
« Reply #7 on: 09/06/2008 11:20:40 »
And on their 60th anniversary, they gave each other...diamonds. :)
 

Offline Madidus_Scientia

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How does carbon dating work?
« Reply #8 on: 09/06/2008 13:27:03 »
and they'll still be dating for a while yet
 

lyner

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How does carbon dating work?
« Reply #9 on: 09/06/2008 14:21:02 »
I heard they broke up spontaneously.
 

Offline SquarishTriangle

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How does carbon dating work?
« Reply #10 on: 09/06/2008 14:48:10 »
Was that before or after the evil man in the white coat threw them in the accelerator mass spectrometer?
 

Offline Bored chemist

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How does carbon dating work?
« Reply #11 on: 09/06/2008 19:44:12 »
The man with the accelerator isn't evil. It's the other sort of carbon dating specialist who has nothiing better to do than wait for carbon atoms to die. Th  guy with the mass spec can tell them apart while they are still alive (though does have to separate them to count them).
 

Offline SquarishTriangle

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How does carbon dating work?
« Reply #12 on: 10/06/2008 02:18:14 »
It's the other sort of carbon dating specialist who has nothiing better to do than wait for carbon atoms to die.

*Will never complain about life again.*
 

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How does carbon dating work?
« Reply #12 on: 10/06/2008 02:18:14 »

 

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