Fossils are a very important marker to know the past history.The fossils are the background for the geological research because only direct fossil can tell us the past environmental history. The fossil may from tree leaf, hard bone or some time the tiny microscopic microorganisms. The index fossil is so important to reveal a specific age of the depositional environments. An index fossil is the specific fossil type which was lived in a certain time and location. Example of Index fossil is Conodont. Conodon can tell us the Permian Triassic Boundary of the geological time across which the biggest Permian mass extinction has occurred at 251.94 Ma.