Fossils are the preserved remains or traces of ancient organisms that can be used to identify the age of rocks. There are several ways fossils can form including mummification in dry places, preservation in amber or tar seeps, freezing, petrification through mineral replacement, carbon imprints, or as molds and casts. Trace fossils are fossilized tracks or burrows that reveal animal behaviors. Index fossils and key beds containing distinctive fossils are used to date rock layers and correlate locations. Together fossils provide evidence of plate tectonics through the past distribution of organisms.

1. Fossils

2. Fossils:
 The trace or remains of an organism that lived long
ago, most commonly preserved in sedimentary rock, can
be used to identify the relative or absolute age of a rock

3. Paleontology
 The study of fossils and ancient organisms

4. Mummification
 Typically occurs in dry places where bacteria can’t
survive

5. Amber:
 Organisms trapped in ancient tree sap

6. Tar Seeps:
 Thick petroleum that comes to the surface and is
covered by water

7. Freezing:
 Low temperatures protect an organism from bacteria

8. Petrification:
 Minerals in water seep in and replace original organic
materials

9. Imprints:
 Carbonized imprints left behind after the organic
material decays

10. Molds and Casts
 Molds are empty impressions filled by rock while casts
are replica of their original organism

11. Gastroliths:
 Smooth stones in the digestive system of dinosaurs to
help grind up and digest food

12. Trace Fossil:
 A fossilized mark that formed in sedimentary rock by the
movement of an animal on or within a soft sediment (i.e.
a footprint)

13. Index Fossils:
 A fossil that is used to establish an age of a rock
because it is distinct, abundant, and widespread, and
only existed for a short span of geological time, can be
used to determine the absolute age of a rock layer

14. Evidence of Plate Tectonics
 Fossils of marine life on mountain tops and shallow
water organisms in deep water prove crustal movement

15. Key Beds:
 Rock layers that contain distinctive characteristics (such
as volcanic ash) or fossil content that allow one to
correlate rock layers in different areas