Fossils are the remains, relics or remains of ancient creatures preserved in rocks, and the most common ones are bones and shells. The word fossil comes from the Latin word fossillis, which means digging. Fossil is the main research object of paleontology, which provides evidence for studying the life history of animals and plants in geological period. Records of fossils in ancient books in China, such as Ji Ran in the Spring and Autumn Period and Wu Jin in the Three Kingdoms Period, all refer to the "keel" produced in Shaanxi, that is, the bones and teeth of ancient vertebrates.
Shan Hai Jing also has a description of "stone fish" (that is, fish fossils); There are descriptions of ancient insects in amber of Tao Hongjing during the Qi and Liang Dynasties in the Southern Dynasties. In Song Dynasty, Shen Kuo had a correct understanding of the origin of snail and mussel fossils and Wandu fish fossils. So far, the earliest bacterial fossils found are filamentous bacterial fossils from Walla Onna group in Australia 3.5 billion years ago.