Fossils are the remains, relics or remains of ancient creatures left in rocks, most commonly bones and shells. 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.
In the long geological age, countless creatures lived on the earth, and many of their dead bodies or traces left by life were buried by the sediment at that time. In the following years, the organic matter in these biological remains was completely decomposed, and the hard parts such as shells, bones, branches and leaves were petrified with the surrounding sediments and turned into stones.
Conditions for the formation of fossils
1, biological conditions: organisms that form fossils must have hard structures, such as biological shells, bones, teeth, trunks, spores, pollen, dried fruits, etc. It is difficult for molluscs to form fossils, such as jellyfish and snails, and it is extremely difficult for hair, skin and muscles of organisms to form fossils. Because hardware is mainly composed of minerals, it has a strong ability to resist various destructive effects.
2. Preservation conditions of biological remains: If the body part of a living thing is crushed, rotted or severely weathered, it may change or cancel the possibility of this living thing becoming a fossil.
3. Time factor: living things must be buried quickly, isolated from the air, and avoid oxidation, otherwise these living things will soon be eaten by other living things or rotted and unable to form fossils. Even hard shells and bones will quickly corrode and melt into the soil.