Answer:
When plant or animals after being alive are preserved in sedimentary rocksis called "taphonomy" or fossilization; when they die in a watery environment, and after soft tissues are decomposed, the hard body parts such as shells and bones are turned into a mold when the sediments harden over time.
High pressure is key to generate the mineralization.
Anoxic preservation is also key, which is the condition of being shielded and safe from oxygen to avoid erosion or corrosion.
And of course, the entity must contain hard body parts that could linger over time.
Step-by-step explanation: