The correct answer is called Correlating
Explanation
Correlating or correlating rock layers is an instrument to determine the age of rocks, it means fossils are used to determine the age of rock layers, for this process it is necessary the fossil had lived a short time so they are sure it appears in only one layer and belongs just to one specific age. Later these fossils are matched to different rocks or layers and thus, different areas with the same fossils can be studied and compared to determine the age of each of the layers above or under the fossil. Also, the word correlation refers to two or more objects, people or other being related to each other as in the case of fossils and rock whose age is related and thus can be correlated or matched up.