Can someone explain the theory behind carbon-dating? It’s been awhile, but IIRC, it’s based on the idea that the carbon last consumed by an animal is retained within the animal’s mortal remains.
A certain percent of the carbon atoms will be Carbon-14 isotopes.
And, with knowledge of the half-live of the C-14 isotope, scientists can approximate the age of the bones, fossil, etc. Can any SDoper elaborate on this?
Thanks! - Jinx 
The theory is something like this :
1> Living things have a certain concentration of C-14 absorbed from the atmosphere in theier bodies. Now why the concentration of C-14 is same in all living things is something I never understood or for that matter why the concentration of C-14 in the atmosphere was same as today is beyond me.
2> Once dead the Concentration of C-14 decreases exponentially.
So Cd = Concentration at the time of death of C - 14
And Cc = Concentration at current time of C-14 in the dead body
So Cc/Cd = exp(-kt) ( t is time, k is a constant) … 1
Half life is the time t(1/2) for Cc/Cd to become 0.5 (1/2)
So, 0.5 = exp(-k*t(1/2))
or k = ln(0.5)/-t(1/2) … 2
So, if you know t(1/2) , you can find out k from (2). Plug, k back into (1) and if you know Cd (assume to be same as the concentration in living things dying now) and measure Cd (the concentration of C-14 in the fossil). You can find t, the time for which the thing has been dead.
The C14 is continually replenished by bombardment of atmospheric nitrogen by cosmic rays. Most of that C14 winds up as atmospheric carbon dioxide. There is no evidence that the ratio of atmospheric C14 to C12 from this process has changed significantly over the practical interval for carbon dating.
Well, there’s a little evidence. Tree ring data shows an anomaly of ± 2% in [sup]14[/sup]C production over the last 1000 years (Fig. 3 here). This site details [sup]14[/sup]C discrepancies over the past ~5000 years.
The first barrier you’ll need to overcome with Carbon dating is actually starting a conversation with a piece. This stage is a lot easier for the Human than it is for the Carbon. This is the trickiest area, as first impressions count - a lot! A piece of Carbon is almost always just automatically interested when a Human comes over and talks to it. Humans, however, are not. They usually make up their mind on whether they want anything to do with an inanimate mineral almost before it even opens it’s mouth. Therefore, the first step, and this goes for both Humans and Carbon, in asking someone out is to be presentable and project confidence.
This only covers the merest first step of Carbon dating, but, if you follow this general advice, you will realise the next steps on your own.
Happy dating!
Coffeeguy
This site gives an abbreviated explanation of several methods for calibrating carbon dating methods.
Hmm…doesn’t this assume the animal is no longer exposed to the atmosphere? So, carbon dating tells us when the animal was eventually buried by, say a mudslide, but it cannot tell us when the animal actually died, correct? So, isn’t this a gross error in using this method? Also, wouldn’t a larger animal have absorbed more Carbon-14 from the atmosphere than, say, smaller animals?
I am reviving this thread as the issue has come up once again in my life…raising new questions about how this can work. Leap of faith, perhaps??? - Jinx
Animals and plants only absorb carbon when they’re alive. Plants get it by photosynthesis, absorbing it from the atmosphere by photosynthesis (take in carbon dioxide; emit oxygen; carbon remains). Animals get it by eating plants or other animals. So as long as the ratio of carbon12:carbon14 in the atmosphere remains constant, the ratio of carbon14 entering organic matter will stay the same.
Dead tissue doesn’t absorb carbon, so once the organism dies, the amount of carbon14 in the organic tissue decreases at a fixed rate.
At least, that’s what I remember from Biology 20. Maybe one of our science types will be along soon to elaborate.
Oh, with regard to size of the organism - that doesn’t matter. It’s the ratio of carbon12:carbon14 in the remains that matters, not the absolute amount of carbon14.