Fossils

Fossils are the remains or traces left of prehistoric life.

1. The chances of being fossilized are improved if:
   • there is rapid burial.
   • the organism has hard parts.
2. There are many types of fossils:
   1. Mold - when a buried shell or bone is dissolved away by underground water. Just shows surface details.
   2. Cast - when a mold is filled with minerals.
   3. Petrified - internal voids filled with minerals.
   4. Replacement - the organism's material is replaced with minerals. Can show microscopic detail !
   5. Amber - hardened resins from trees trap organisms.
   6. Carbonization - fine sediments encases organism. Pressure over time leaves only a thin layer of carbon.
   7. Impression - when carbon of carbonization is lost, leaving just details in sediment.
   8. No change - more recent organisms may not be altered. Example: mastodon teeth on the island.
   9. Traces - indirect evidence of life:
      • Burrows - the Devil's Corkscrew.
      • Tracks -
      • Coprolites - droppings.
      • Gastroliths - stomach stones.
3. Fossils can be used to correlate (show relationships among) sediments.
   1. William Smith (1769-1839). English canal builder who noticed each rock strata contained unique fossils.
   2. Smith used fossils to correlate strata over wide areas.
   3. Principle of biotic succession: fossil organisms succeed one another in a definite and determinable order. Time periods can be recognized by its fossil content.
   4. Certain organisms are widely distributed but lived for a short time. These fossils are called index fossils.