Which method is extensively used to define evolutionary relationships ?

Explanation

Fossils are the remains or impressions of the dead animals and plants that lived in the past.
Fossils are the direct evidence of evolution. If the fossils are found closer to the surface then they are more recent than the fossils found in deeper layers. One can find evolutionary relationships between ancient and present organisms by study of fossils.
We also come to know the time period of evolutionary process by studying fossils.