Theory behind carbon dating
By measuring the ratio of the radio isotope to non-radioactive carbon, the amount of carbon-14 decay can be worked out, thereby giving an age for the specimen in question.
But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.
Voila, now you can tell how old a sample of organic matter is.
Some notes: 1) Obviously, this technique only works for dead organic material.
On the other hand, if tons of half-lives have passed, there is almost none of the sample carbon 14 left, and it is really hard to measure accurately how much is left.
Animals, including humans, consume plants a lot (and animals that consume plants), and thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms.The majority of 14C on earth comes from the atmosphere where it is created when cosmic rays hit nitrogen molecules in the atmosphere.Because of this, the amount on earth is very consistent.When the plant dies it no longer gets any more carbon and the amount of C-14 will start to decrease.We can take a plant sample and measure the amount of carbon in it and from that we can calculate how radioactive it should be.
Search for theory behind carbon dating:
This equilibrium persists in living organisms as long as they continue living, but when they die, they no longer 'breathe' or eat new 14 carbon isotopes Now it's fairly simple to determine how many total carbon atoms should be in a sample given its weight and chemical makeup.