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.