What is a fossil?

Fossils are witnesses of past life forms and past habitats. It is usually remains of a living element (animals, plants, humans...) or it can be traces (dinosaur footprints, different layers of a mountain...). A fossil is always preserved by natural process. Geologist can check the age of a fossil through radiometric dating methods. Fossils are very rare. The living creature needs to die in the right place. Meaning it needs to die on a seabed or on a river bed. There are no scavengers and no elements to disturb the process. Then time will do it's job. The chemicals and minerals will create a reaction that will start the recrystallization. After many, many years the rocks will erode and start pushing the fossils towards the top. That's the moment where the archeologist or geologist will find it. If not the fossil will just dissolve into sand, silt or mud.