Fossils and Geologic Time Topics

• Introduction
• Fossil Basics
• Methods of Preservation
  1. Petrifaction
  2. Perminera-
     lization
  3. Carboniza-
     tion
  4. Molds and Casts
• Important Animal and Plant Fossils
• Selected Virginia Fossils
• Tips For Fossil Collecting
• Geologic Time

Methods of Fossil Preservation (Part 2)

Carbonization

• 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)

Molds and Casts

• 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)

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