How do fossils help in understanding the history of Earth?

Fossils are described as the remains of the hard parts of life-forms found in rocks.Rocks form sediments and a cross-section of earth's crust indicates the arrangement of sediments one over the other during the long history of earth. Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment. Fossils help in understanding the history of Earth by showing the arrangement of sediments and indicating the geological period in which life-forms existed.The study of fossils in different layers shows that life-forms varied over time and that new forms arose at different periods in Earth’s history.A study of fossils in different sedimentary layers indicates the geological period in which they existed. The study showed that life-forms varied over time and certain life forms are restricted to certain geological time- spans. Hence, new forms of life have arisen at different times in the history of earth. All this is called paleontological evidence.