Definition:Radiometric Dating/Radiocarbon Dating

Definition
Radiocarbon dating is a specific application of radiometric dating which is used to determine how long a piece of organic matter has been dead.

Because of bombardment by cosmic rays, the ratio of (radioactive) carbon-14 to (stable) carbon-12 in the atmosphere of Earth is fairly constant.

This ratio is known.

The ratio of carbon-14 to carbon-12 in a living organism is the same as it is in Earth's atmosphere, by biological respiration.

However, when the organism dies, it no longer respires, and the carbon in its body stays where it was at the time of its death.

As time passes, the carbon-14 decays to nitrogen-14 via the process of beta decay.

The half-life of carbon-14 is known to be $5700 \pm 40$ years.

Also see

 * Formula for Radiocarbon Dating