Question

What parts of an organism become a fossil?

Answer 1

Usually the hard parts of an organism become fossilized.

Explanation:

The soft parts often disintegrate before they can be turned to stone (petrified)
The hard parts can be preserved and slowly one molecule at a time replaced by minerals . Most fossils have been petrified or turned to stone.
Some fossils are preserved soft parts but they are not common. One example would be the preservation of footprints The footprints are covered by a layer of sediments before the footprint can be erased by wind, water and other forms of erosion.