[AndyTheBear]

Eeek, I will take your word that C14 becomes Nitrogen 14. And upon reflection I agree it always makes it appear younger...whether or not its added before or after death. The only cases of it making something appear younger is if the control sample one uses to estimate the ambient C14 was what got extra C14 added.

But the ratio between C14 and normal Carbon will decline on a curve, not linearly due to half life. If I start with 1024 marbles and every day somebody takes away half of them the sequence would be:

day 1: 1024
day 2: 512
day 3: 256
day 4: 128
day 5: 64
day 6: 32
day 7: 16
day 8: 8
day 9: 4
day 19: 2
day 20: 1

Between day 1 and 2 I lost 512 marbles. Between day 19 and 20 I only lost 1. Thus if I chart the number of marbles divided by some constant denominator or any other constant unit, I will have a curve that declines more quickly and than slows its decline. The half life is a constant sure, but the half life is the second derivative. The first derivative is not constant.

[calenel]

Half-lives are the result of (mathematical) exponential decay of the form Ae^-kt, where A is the amount you start with, t time and k is some value specific to the isotope in question (and e is Euler's number, of course). The linear term is in the exponent. None of the derivatives are constant - I don't think I said that. But the amount of time it takes for half of any given amount to decay is constant, which is what I intended to convey. If we assume that (continuing your marbles metaphor) everybody starts out with 1024 marbles, we can determine how long they've been losing their marbles by how many they have left. That is the gist of carbon dating (or any of the other similar radio-dating methods). Of course, with 14C they have discovered a few anomalous years where 14C seems to have been produced in substantially larger quantities than typically, perhaps due to solar activity or some star going nova somewhere, making 14C dating less accurate than it is portrayed, but that is a side note.