READ: Important Vocabulary Terms

READ: Important Vocabulary Terms

• A fossil is any remains or traces of an ancient organism. 
  
• Body fossils are left behind when the soft parts have decayed away. 
  
• Trace fossils are remains such as burrows, tracks, or fossilized poop. 
  
• Amber ancient tree sap that can contain preserved organisms. 
  
• Permineralization: After a bone, wood fragment, or shell is buried in sediment, mineral-rich water moves through the sediment. This water deposits minerals into empty spaces and produces a fossil. Fossil dinosaur bones, petrified wood, and many marine fossils were formed by permineralization.
  
• Mold: When the original bone or shell dissolves and leaves behind an empty space in the shape of the material, the depression is called a mold. 
  
• Cast: Sediments that have filled in a mold that is the shape of the original organism or part. Many mollusks (clams, snails, octopi, and squid) are found as molds and casts because their shells dissolve easily.
  
• Replacement: The original shell or bone dissolves and is replaced by a different mineral. 
  
• Compression: Some fossils form when their remains are compressed by high pressure, leaving behind a dark imprint. 
  
• An index fossil can be used to identify a specific period of time. Organisms that make good index fossils are distinctive, widespread, and lived briefly. Their presence in a rock layer can be used to identify rocks that were deposited at that period of time over a large area.