Fossils and their formation

The formation of fossils is known as fossilisation: it is a rare phenomenon that occurs under specific conditions and is particularly supported by aquatic environments. Fossilisation is a process of mineralisation, in other words the replacement of living tissue by mineral substances. It mostly involves the hard parts of organisms such as bones, teeth and shells because these elements are mineralised and more resistant to degradation. The soft tissues such as skin, muscles and internal organs decompose quickly, disappear more easily and are therefore rarely preserved. Certain organisms fossilise better than others so fossil biodiversity is not an accurate reflection of past biodiversity.

A fossil is the remains or trace of an animal or plant that lived in the past and the organic particles of which have been transformed into mineral particles.

The discovery of a fossil can be a matter of luck or can be the result of targeted research and it is rare to uncover complete organisms. Palaeontology is the science that analyses fossils, their living environment, their evolution and the relationships between species. Most of the time, palaeontologists initially examine the discovered remains in situ and then in the laboratory.

Ammonite (Cephalopod)

Lower Jurassic, Sinemurian

From - 199 to - 190 Ma

1. An ammonite in its natural environment.
2. When it dies, the ammonite settles on the sea floor. The soft tissues decompose.
3. Gradually sediments cover and fill the shell.
4. Eventually the shell becomes completely buried. Fossilisation begins.
5. Fossilisation is under way. The process lasts millions of years.
6. The ammonite is exposed on the surface of the rock through erosion, folding, etc.
7. Palaeontologists can now extract the fossil using special tools.