The study of fossils, i.e. palaeontological evidences support theory of organic evolution, i.e. evolution in plants and animals. The transitional fossil organisms show evolutionary relationship between two groups and are called connecting links, e.g. Archaeopteryx is a connecting link between reptiles and birds.
The study of fossil in different sedimentary layers indicates the geological period in which they existed, the life forms varied over time and life forms that are restricted to certain geological time scale. Hence, new forms of life have evolved at different times in the history of earth. All this forms palaeontological evidence. The ages of these fossils are estimated by using methods like radiocarbon and ting.