As it's difficult to determine the absolute age of the rocks the scientist measures the relative ages of rocks as the ages are a comparative study of the risks by the scientists and the geologist as they map the earth for the various sources.
There findings of the carbon signatures of the rocks and hence tend to give the presence of older and younger rocks composition on earth like the sedimentary rocks are arranged in the strata and layered information hence os easy to point out the exact or specific year of the rock.
