2. REMAINS OR TRACES OF PREHISTORIC LIFE Inclusions found in sediment & sedimentary rocks A Tool for interpreting the geologic past Important time indicators

3. Unaltered Remains – original parts are still intact Altered Remains – parts are changed “Turned into Stone” Trace Fossils – indirect evidence of prehistoric life

4. Conditions Favoring Preservation Rapid burial protects soft parts from environment Possession of hard parts Better chance of being preserved The Record of life in geologic past is incomplete Only 10% of all past life on Earth has been preserved in the rock record, fossilized.

5. PETRIFICATION MOLDS & CASTS CARBONIZATION PRESERVATION TRACE FOSSILS

6. O rganic matter is completely replaced by minerals “ The fossil is turned to stone ” Permineralization Cavities & pores are filled with precipitated minerals Replacement Original Cell material is replaced with mineral Microscopic details visible

7. IMPRESSIONS (Imprints) A replica of organisms surface preserved in sedimentary rock Two types: Molds - shell or other structure is buried, then dissolved leaving a hollow cavity Cast - hollow space of mold fills with minerals Replica of the original organism

9. Pressure squeezes out liquids and gases from buried organic matter leaves behind a thin residue of carbon

10. AMBER PRESERVATION Organism preserved in hardened resin of ancient trees (tree sap) Resin surrounds organism preventing decay

11. FREEZING (DESICCATION)

12. Preservation in Tar Smilidon

13. Indirect evidence of prehistoric life Tracks Burrows Gastroliths Stomach stones used to grind food Coprolites Fossil dung stomach contents

14. Two major scientific developments help explain the fossil record: Theory of Evolution – Charles Darwin Life forms have evolved over time from simpler to more complex life forms Mechanism - “Natural Selection” Individuals that are better adapted to their environment are more likely to survive and reproduce than others of the same type. Adaptation – organisms possess certain traits that affect their ability to survive and reproduce.

15. Principle of Fossil (Faunal) Succession (One of the most important principles in historical geology) Fossil organisms succeed one another in a definite and determinable order Fossil content can interpret geologic time period.

16. Fossil remains of living things are present in the rock layers at different locations and exist with a discrete period of time Any time period can be recognized by its fossil content Age of rock unit “A” Age of rock unit “B”

17. INDEX FOSSILS Widespread Geographically Occur in large numbers Limited to a short span of geologic time

18. Correlation matching of rocks of similar ages in different regions Correlation often relies upon fossils William Smith (late 1700s) - sedimentary strata in widely separated area could be identified and correlated by their distinctive fossil content

20. Fossils can be important indicators of past environments & temperatures Compared to current environments an living organisms Ripple marks & Mud cracks

23. Fossil Teeth Teeth with Flat surfaces for grinding vegetation Fossil pollen from grasses in same rock layer Indicates animals lived in a grassland environment Sharp teeth for eating meat Abundant fossils of plant eaters Indicates plant eaters were main food source for meat eaters.

24. Clam shells – limestone; shallow seas Thick shelled fossil animals – inhabited shorelines with pounding & surging waves Thin Shelled Fossil animals – lived in deep, calm offshore waters Fossilized Coral – warm tropical marine environment Type & positioning of fossils can indicate positions of ancient shorelines