The carbon-14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with molecules of nitrogen (NFigure 1: Diagram of the formation of carbon-14 (forward), the decay of carbon-14 (reverse).
Carbon-14 is constantly be generated in the atmosphere and cycled through the carbon and nitrogen cycles.
The entire process of Radiocarbon dating depends on the decay of carbon-14.
This process begins when an organism is no longer able to exchange Carbon with their environment.
The time that it takes for half of a sample to decay is known as the half life of the isotope.