Fossils are most often formed from organisms that have a solid and resistant skeleton. Hard parts, such as bones and teeth, are more likely to survive the ravages of time compared to their softer counterparts, which tend to decompose rapidly. When an organism with such hard parts dies and is quickly buried, this sets the stage for the long, slow process of fossilization.

Once buried, the hard parts of the organism undergo a transformation. Over time, minerals from the surrounding sediment seep into the pores of the bones or shells. This mineral infusion can turn the organic material into stone, preserving the shape and structure of the original organism. In some cases, the original material is completely replaced by minerals, creating a detailed stone replica.

Some soft tissues can fossilize, though this is rare. Insects trapped in amber or mammoths preserved in ice are examples of how soft tissues can be fossilized under exceptional conditions.