How do most fossils form?
Most fossils form when the organism is buried under water bourn sediments and then the organic material is replaced by mineral materials.
Most fossils are found in sedimentary layers. The placement of the fossils in thick sedimentary layers indicates that the organic material was buried under sediments of an aquatic nature.
The fossils most frequently found are mineralized, such as fossilized wood. The organic material is dissolved and replaced by minerals.