Answer: Index fossil correlation
Relative dating refers to the age estimation method in which the order of the past events is determined to compare the age of an object, rock or organism with the respect to the other. This method gives the estimated or approximate age of the entity under consideration. It does not give the absolute age. Index fossils are the fossils which are found in a particular geological time. They have a short life span and wide geographical distribution. These fossils can be used to determine the relative age. As, these fossils can be compared with the layers of strata and rocks, where they are found, to know their approx age.