From the rock record and fossil record, scientists can infer the history of the Earth and the changes that have occurred over time. The rock record provides information about the physical and chemical properties of rocks and their formation, while the fossil record provides evidence of the past life on Earth.
One specific example of evidence from the rock record is the principle of superposition. This principle states that in a sequence of undisturbed rocks, the oldest rocks are at the bottom and the youngest rocks are at the top. By studying the order of rock layers, scientists can determine the relative ages of the rocks and the events that occurred during their formation.
Another example of evidence from the fossil record is the concept of index fossils. Index fossils are fossils of organisms that lived during a relatively short period of geologic time and were widespread, making them useful for dating rocks and correlating geologic events. For example, the trilobite species Phacops rana is an index fossil of the Ordovician period, which helps scientists to identify and date rocks of that age.
Overall, the evidence from the rock and fossil record helps scientists to organize geologic time by providing a relative timeline of events and the evolution of life on Earth.