# Silly question about real-world carbon-dating decay calculation

I came across a PreCalc decay problem dealing with trying to date an old piece of wood found at a archaeological dig. The half-life of carbon-14 was given as 5600 years.

The problem was: 2% of the original carbon amount remains. When was the tree cut down?

My question is: How do they know the original amount of carbon-14 in the wood? Did someone plant a new tree of the same type and measure the initial amount of carbon-14?

Also, is the amount of carbon-14 uniform across all samples of this wood? Does it start and decay exactly the same for all samples of this type of wood? What if it's just a particularly high concentration in this piece of wood b/c of was facing the sun (or whatever) Would you take several samples from the wood?

Also, does this belong in some Science subforum?

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This belongs in another forum. – copper.hat Feb 5 '13 at 19:22
The tinier the sample, the more variation there is. More samples is always better. If sample is very old, little Carbon $14$ is left, so measurements are unreliable. There is some variation caused by conditions, not a large amount. There have also been variations in the relative amount of Carbon $14$ in the atmosphere. A huge amount of work has been done to refine the basic idea used in textbook examples. – André Nicolas Feb 5 '13 at 19:34