What is the best method of radioactive decay for something that is approximately 48,000 years old?

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Carbon dating is the best method of radioactive decay.

Explanation:

Radio carbon dating or carbon dating is a method of finding the age of the object containing "organic material" using isotopes of carbon. It is used to measure residual radioactivity. Carbon "14 is an isotope" of carbon which is weakly radioactive. This is formed in the "upper atmosphere" with cosmic ray neutrons effect on nitrogen 14 atoms. Radio carbon dating results represent when the organism was alive but not in use.