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furshur
SFN Regular
USA
1536 Posts |
 Posted - 01/30/2004 : 13:41:50 [Permalink]
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Jarrid,
Just a little more on how radiometric dating is done.
Carbon-14 (6 protons & 8 neutrons) decays to Nitrogen (7 protons and 7 neutrons). It is called beta decay - esentially a negative charge flys out of a neutron, 'turning it' into a proton. Carbon-14 has a halflife of ~5730 years
So....
If you have 1 gram of Carbon-14 initially the following would be true:
Year 0............1 grams of C-14,........0 grams of N
Year 5730.......0.5 grams of C-14,......0.5 grams of N
Year 11460.....0.25 grams of C-14,.....0.75 grams of N
Year 17190....0.125 grams of C-14,....0.875 grams of N
Year 22920...0.0625 grams of C-14,...0.9375 grams of N
and so on.
Whatever the amount of C-14 you have, in 5730 years 1/2 of it will be gone.
As stated earlier C-14 is a little different than some other types of dating because the STARTING amount of C-14 is based on the amount that a living thing has at death. The C-14 in a body should be at an equilibrium with the percentage of C-14 in the environment.
When the organism dies the clock starts so to speak. That is, no more C-14 will be metabolized by the organism so the C-14 level should not increase after death. So if a certain sample of living wood has X amount of C-14 in it, and a wood sample tested has 1/4 of that amount, then the sample is 11,460 years old.
There are some difficulties that have to be taken into acount. The equilibrium level of the C-14 at the time of the organisms death, the possibility of the introduction of C-14 contamintaion in to the sample and others. But this is a very powerful tool that has been verified by many different methods.
This is simplified somewhat but it is generally how the testing is done.
Hope this helps.
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If I knew then what I know now then I would know more now than I know. |
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Jarrid
Skeptic Friend
101 Posts |
Posted - 01/30/2004 : 15:50:46 [Permalink]
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| Ok...I think I understand what you are saying. You used the example of wood, and if wood has X amount of C-14..etc...how do you know what the X amount is so that you can find out that there is only 1/4th of it left? |
I don't have to go swimming through an outhouse to know I wouldn't like it." |
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filthy
SFN Die Hard
USA
14408 Posts |
Posted - 01/30/2004 : 16:28:43 [Permalink]
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There doesn't seem to ba anything fresh on Toumai, so I'm putting up a couple of older articles.
http://www.primeorigins.co.za/news/994720.htm
This one pretty much covers the discovery.
http://www.smh.com.au/articles/2002/07/13/1026185124750.html
And here is the other side of the argument. It in interesting to note that if it is indeed a female gorrila, it is still equally valuable for research.
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"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist! 
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jmcginn
Skeptic Friend
343 Posts |
Posted - 01/30/2004 : 16:40:38 [Permalink]
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Jarrid,
quote:
Ok...I think I understand what you are saying. You used the example of wood, and if wood has X amount of C-14..etc...how do you know what the X amount is so that you can find out that there is only 1/4th of it left?
Because we know the atmospheric percentage of C-14 thus we know the original C-14 in the piece of wood since it will be the same percentage. This is because trees get all of their carbon from the atmosphere as do all plants. (We animals get our carbon from plants thus our C-14 levels are also the same as the atmosphere).
Edited to add the following:
For example if we had a 100g sample of carbon from a piece of wood. And we knew that the atmosphere concentration of C-14 was 1% of all carbon in the air (this is not the real percentage mind you). Then we would know that the time the tree died this sample would have had 1g of C-14 in it. If we found it really had 0.5g then we would know the wood was ~5700 years old. |
| Edited by - jmcginn on 01/30/2004 16:44:31 |
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jmcginn
Skeptic Friend
343 Posts |
Posted - 01/30/2004 : 16:41:43 [Permalink]
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Dave,
Thanks, I had a long hiatus due to both work and school, but now I am taking a semester off so more time to have fun :> |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/30/2004 : 20:48:46 [Permalink]
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Cool, jmcginn. Pardon if I've forgotten, but what are you schooling for, and how much do you have left before reaching whatever goal it is that you've got right now?
Back to radiocarbon dating: it should perhaps be noted that although carbon-14 is slightly heavier than the non-radioactive carbon-12, the two act the same ways chemically. In other words, when simple chemical reactions are occuring, there's no preference for one or the other. Plants, for example, process the carbon dioxide (one carbon atom, two oxygen atoms) they inhale the same way, whether the carbon in that molecule is radioactive or not.
That's why the carbon in living things is found in the same percentages of C-12 and C-14 as exist in the atmosphere: plants, animals, bacteria (etc.) simply can't tell the difference.
(Interesting side note: found a reference which says there are about 15 decays per minute per gram of carbon in living creatures. That's 180,375 decays per minute in an average 65-kilo human, or about 95 billion decays per year. That's about 0.00221 nanograms of carbon turning into nitrogen every year, inside us. Thankfully, we're highly redundant in terms of molecular processes, but it's still just a little freaky to think about...) |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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jmcginn
Skeptic Friend
343 Posts |
Posted - 02/02/2004 : 09:25:57 [Permalink]
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Dave,
I am returning to school after a long break. I majored in biology and chemistry my first run around and nearly completed but then dropped out for the lure of the computer industry (I'm a software engineer now). Now I am returning hoping to eventually get my doctorate in physical anthropology. My main interest is platyrrhine evolution (New World monkeys).
Interesting notes on the decay rates. That's allot of radioactive decay going on in our own bodies from the very building blocks of our own body including even our own DNA ;> |
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