What unstable isotope would be best to refine the date of bones found in a cave hearth built by humans between 30,000 and 50,000 years ago?

Carbon - 14 Isotope

Explanation:

Carbon - 14 is an unstable and weak radioactive carbon isotope that is used to determine the age of an organic matter (i.e Carbon Dating).

The unstable isotope that would be best to refine the date of bones found in a cave hearth between 30,000 and 50,000 years ago is carbon-14 (C-14). Usually, C-14 is used to estimate the age of decomposed organisms that existed within any age less than 50,000 years ago from a recent date; therefore, C-14 would be best for any age between 30,000 and 50,000 years ago.