1. Geologic Time and Earth History

2. Two Conceptions of Earth History:
Catastrophism
Assumption: Great Effects Require Great Causes
Earth History Dominated by Violent Events
Catastrophes Do Happen But Are Uncommon
Uniformitarianism
Earth History Dominated by Small-scale Events Typical of the Present.
Such events as erosion and deposition

3. Fossil Ripple Marks, Baraboo Range

4. Modern Mud Cracks

5. Fossil Mud Cracks, Virginia

6. Two Kinds of Ages Relative - Know Order of Events But Not Dates
Civil War Happened Before W.W.II
Bedrock in North America Formed Before The Glaciers Came
Absolute - Know Dates
Civil War
World War II
Glaciers Left N.A. About 11,000 Years Ago

7. Superposition: Mindoro Cut, Wisconsin

8. Remains of Ancient Plants And Animals, Evidence of Life
Fossils
Remains of Ancient Plants And Animals, Evidence of Life

9. Commonly Preserved: Hard Parts of Organisms: Bones Shells
Hard Parts of Insects
Woody Material

10. Rarely Preserved Soft or Easily Decayed Parts of Organisms:
Internal Organs
Skin
Hair
Feathers

11. Types of Fossils Original Material Casts & Molds
Replacement (Petrified Wood)
Carbonized Films (Leaves)
Footprints, Tracks, Etc.
“Trace Fossils” – Our only preserved record of behavior of fossil organisms

12. Dinosaur Tracks, Texas

13. Natural or Sculpture?

14. Where Fossils Occur Almost Exclusively in Sedimentary Rocks
Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil
Rare Exceptions:
Some Fossils in Low-grade Metamorphic Rocks
Trees Buried by Lava Flow
To Be Preserved, Organisms Have to Be:
Buried Rapidly After Death
Preserved From Decay

15. Fossil Tree in Lava Flow, Hawaii

16. CORRELATION
The process of matching up rock layers from different locations.

17. Correlation

18. Absolute Ages: Early Attempts
Salt in Ocean
If we know rate salt is added, and how much salt is in ocean, can find age of oceans.
Sediment Thickness
Add up thickest sediments for each period, estimate rate.
Both methods gave age of about 100 million years
Problem: Rates Variable

19. The Fundamental Rule of Absolute Ages
The Earth is older than everything on or in it
-Except its atoms
-All ages are minimum ages

20. Some Geologic Rates Cutting of Grand Canyon 2 km/3 m.y. = 1 cm/15 yr
Uplift of Alps
5 km/10 m.y. = 1 cm/20 yr.
Opening of Atlantic
5000 km/180 m.y. = 2.8 cm/yr.

21. Some Geologic Rates Movement of San Andreas Fault
5 cm/yr = 7 m/140 yr.
Growth of Mt. St. Helens
3 km/30,000 yr = 10 cm/yr.