• Soft tissues can be preserved as carbon films. This process is called carbonization.
These carbonized plant fossils were preserved as a thin carbon film. (Photograph by Parvinder Sethi)
• Many fossils are molds or casts. Molds form when the original material has been removed, leaving a cavity with the same shape as the organism. Casts form when molds fill with new material.
This sample shows both molds and casts of brachiopods. The square contains a mold, or the print of an original shell. The oval contains a cast, a sediment-filled cavity. Brachiopods are clam-like organisms with two shells. (Photograph by Parvinder Sethi)