Answer:
By calculating the amount of decayed daughter elements.
Step-by-step explanation:
The age of the rock in years is considered as its absolute age. The absolute age is found by determining the concentration of some radioactive elements in the rock. At the time of the formation of rock, small concentrations of radioactive elements get comprised usually. With the passing of time, the parent radioactive elements go through decay process at a regular rate into non-radioactive daughter elements. By calculating the rate at which decaying of a parent element takes place and then by finding the proportion of parent element to the daughter element in the rock, the age of rocks in years can be calculated.