Old Dominion University
A to Z Index  |  Directories


Terri Mathews




GEOL442

GEOL 302

GEOL 110

GEOL 112

GEOL 110 lab




Geology 110


 Fossils 



Learning Objectives



A fossil is the trace or remains of a once living organism.

Fossilization is more likely if the organism has hard parts (bones, shells) and is buried rapidly.  There are different ways that a fossil can be preserved:

A) Direct Fossilization: fossilization of the organism
 

    1) Unaltered Hard Parts: the actual hard part (shell or bone) is simply buried and remains intact.

2) Altered Hard Parts:

      Replacement: mineral material replaces the tissues of the organism molecule by molecule.

Permineralization: mineral material is deposited within the cells of the organism.  If the mineral material is dissolved then some of the original organism will remain.

    3) Carbonization: Pressure from overlying rock strata squeeze organic compounds out of an organism leaving a carbon film behind.  Common method for soft organisms.

4) Mold: the depression left behind by an organism.  Retains detail of the external structure.

5) Cast: a mold that has been filled in with mineral material.

6) Other: some rare methods of fossilization: these methods tend to preserve soft tissue and in some cases the skin and hair of an organism.

B) Indirect Fossilization: no part of the organism remains or is represented but there is evidence that the organism existed.

    1) Tracks, Trails, Footprints

2) Gastroliths: gizzard stones

3) Coprolite: preserved dung

4) Artifacts: useful for studying human evolution.





Fossils can also help reconstruct past environments:

Paleoecology: The study of ancient ecosystems.  Geologists look at modern ecosystems and the hard parts contained within to understand ancient ecosystems.

An understanding of paleoecology can help geologists determine:

    Ancient Environments
    Paleolatitudes
    Geographic movements
    Presence of Land Bridges