For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.Stratigraphy is a branch of geology that studies rock strata with an emphasis on distribution, deposition, age and evidence of past life.Steno's idea that fossils are older than the rock in which they are found hints at this principle, but Hutton is most often given credit for this principle.states that fossil organisms succeed one another in a definite, irreversible, and determinable order.The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.Nicolas Steno, William Smith, Georges Cuvier, Alexandre Brongniart, and James Hutton developed the basic rules for the science of stratigraphy.Relative dating uses the principles or laws of stratigraphy to order sequences of rock strata.These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.
Steno also noticed that fossil seashells could be found in rocks and mountains far from any ocean. Steno proposed that if a rock contained the fossils of marine animals, the rock formed from sediments that were deposited on the seafloor. Relative age means age in comparison with other rocks, either younger or older.Fossils are important for working out the relative ages of sedimentary rocks.Throughout the history of life, different organisms have appeared, flourished and become extinct.In a family like this it’s hard to tell how people are related simply by age. Early geologists had no way to determine the absolute age of a geological material.With rock units we use certain principles to tell their ages relative to each other. If they didn’t see it form, they couldn’t know if a rock was one hundred years or 100 million years old.What they could do was determine the ages of materials relative to each other. They could also determine when a process occurred relative to those rocks. The laws of stratigraphy can help scientists understand Earth’s past.