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.

What is the minimum age for carbon dating?

Since there are practical limits to the age range of the method, most samples must be younger than 50,000 years and older than 100 years. Most samples require chemical pre-treatment to ensure their purity or to recover particular components of the material.