C (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago, although special preparation methods occasionally make accurate analysis of older samples possible.

Is radioactive decay random?

Radioactive decay is a random process. Although the rate of decay for a specific radionuclide can be calculated from knowledge of the number of radioactive atoms and the half-life, there is no way of knowing which specific radioactive atom will decay in which time interval.