Answer:
The correct option is A. Measuring radioactive decay of element isotopes
Explanation:
At the time of formation of rock, certain kinds of radioactive isotope elements get trapped in the rock. These radioactive isotopes are unstable and decay over a period of time forming daughter elements. A rock which will have more number of radioactive elements will be newer to a rock containing non-radioactive daughter elements.
The radioactive decay of each element can be measured by the half-life of elements. This is the primary technique to determine the absolute age of a rock.
