Evidence that evolution of life forms has indeed taken place on earth has
come from many quarters. Fossils are remains of 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. Some of them appear similar to modern
organisms (Figure 6.2). They represent extinct organisms (e.g., Dinosaurs).
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 timespans. Hence, new forms of life have arisen at different times in the history
of earth. All this is called paleontological evidence
