Question

What happens to soft parts of organisms when cast fossils form?

Answer 1

It decays in sediment, the hard parts particularly the bones are left behind. if an organism completely dissolves in sedimentary rock, it can leave an impression.

Answer 2

Answer:

The soft parts of the organisms get decompose, leaving the hard bones or shells behind. Over the period sediments forms over the top of the hard bones or shells which hardens it into a rock. Hard bones and shells forms cast. Cast fossils are formed when plant, animal, or organism die and get buried between layers of mud and silt.