1. Earth History
What Fossils, Rocks, Rock Formations, and Life Tell us about the Age of the Earth?

2. Interpretation of Evidence
What do you see?

3. Interpretation of Evidence
We can all see the same evidence, but we may not all “see” the same conclusion.
What do we do about that?
How can the scientific process (i.e. method) help us develop more reliable answers about Earth’s past?
Does this get everyone to the same conclusion?

4. Evidence of the Earth’s Age
Fossils
Age of rocks
Rock Formation
Clues we Use

5. Fossils What is a fossil?
The remains or imprint of an ancient organism
There are plant and animal fossils

6. Fossils Conditions needed for fossil formation
Organisms made with hard parts like bones, teeth, etc. will fossilize better.
Soft-bodied organisms like jellyfish will deteriorate before fossils can form.
Protection from scavengers and the elements
Rain. Blowing sediments can wear away bone.

8. Types of Fossil Preservation
Mineral Replacement
Organism dies and leaves hard remains (e.g. bones) in soil.
Empty spaces in bone fill with minerals via groundwater
Original organic material decays leaving permineralized remains
Permineralized remains – fossils, which spaces are filled with groundwater.
DNA is usually destroyed

9. Types of Fossil Preservation
Carbon Films
Sediments bury dead organism
Sediments pile up; heat and pressure build
Gases and liquids are forced from the remains
Thin carbon film is left

10. Types of Fossil Preservation
Molds and Casts
Sediments bury dead
organism
Compaction and cementation turn sediment surrounding remains into rock
The remains dissolve and leave a cavity called a mold.
The mold fills with sediment and a cast is made
Cast
Mold

11. Types of Fossil Preservation
Trace fossils
Fossilized tracks or other evidence that suggest the activity of an organism
Dinosaur tracks or burrows

12. Types of Fossil Preservation
Original remains
Can sometimes be preserved in amber or ice. (Like on Jurassic Park)

13. Fossils
Index fossils – remains of species that existed on Earth for a short time, were abundant, and were widespread geographically.

14. Summary Fossils Relative Age of Rocks What conditions are required?
What types are there?
What are index fossils?
Relative Age of Rocks
Laws
Unconformities