Fossils are used by scientists to construct geologic time scales , that are determined by rock formations and other geologic information. Fossils can be used to determine the time period an unknown rock layer was deposited. Certain fossils have been found to occur only in specific layers of rock. Fossils that have this characteristic are called index fossils. When scientists find index fossils in rock layers in different locations, they are able to establish time relationships between these areas.
Fossils also help scientists speculate about past environments at the time of sediment deposition.
Information about the climate and sediment deposition can be hypothesized. Fossils are responsible for our way of life. Coal, oil, and natural gas are fossil fuels that are the remains of prehistoric plants and animals. These organisms died and were trapped beneath layers of sedimentary rock and lost most of the minerals they contained, leaving mostly carbon. The remaining carbon was heated to form fossil fuels.