Radioactive dating involves determining which of the following?

Half-life decay

Index fossils

Depth of layers

Geologic time

I'm pretty sure the answer is half life decay, we did an experiment in my science class on it last year.

Half-life decay

Explanation:

Radiometric dating or radioactive dating, as it is also known, is a very useful procedure to determine the age of different ancient elements like minerals and rocks, comparing the present amount of a certain isotope which is radioactive in the material with its decay products, through the use of established decay standards.