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
Uniformitarianism
Assumption: We Can Use Cause And Effect to Determine Causes of Past Events
Finding: Earth History Dominated by Small-scale Events Typical of the Present.
Catastrophes Do Happen But Are Uncommon

3. Uniformitarianism Continuity of Cause and Effect
Apply Cause and Effect to Future - Prediction
Apply Cause and Effect to Present - Technology
Apply Cause and Effect to Past – Uniformitarianism
The Present is the Key to the Past

4. Ripple Marks, Bay Beach

5. Fossil Ripple Marks, Baraboo Range

6. Modern Mud Cracks

7. Fossil Mud Cracks, Virginia

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

9. Superposition: Mindoro Cut, Wisconsin

10. Geologic Map

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

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

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

14. 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

15. Dinosaur Tracks, Texas

16. Rubbing Rock? Wisconsin

17. Rubbing Rock? California

18. Pseudofossils
Look Like Fossils But Aren't
Dendrites
Concretions

19. Pseudofossils

20. Natural or Sculpture?

21. Johannes Beringer’s “Fossils”

22. Beringer’s Book

23. 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

24. Fossil Tree in Lava Flow, Hawaii

25. Good Index Fossils Abundant Widely-distributed (Global Preferred)
Short-lived or Rapidly Changing

26. Correlation

27. The Geologic Time Scale
Quaternary
Latin, “fourth”
1822
Tertiary
Latin, “third”
1760
Cretaceous
Latin creta, “chalk”
Jurassic
Jura Mountains, Switzerland
1795
Triassic
Latin, “three-fold”
1834
Permian
Perm, Russia
1841
Carboniferous
Carbon-bearing
Devonian
Devonshire, England
1840
Silurian
Silures, a pre-Roman tribe
1835
Ordovician
Ordovices, a pre-Roman tribe
1879
Cambrian
Latin Cambria, “Wales”

28. Absolute Ages: Early Attempts
The Bible
Add up Dates in Bible
Get an Age of B.C. For Earth
John Lightfoot and Bishop Ussher B.C. (1584)
Too Short

29. 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

30. Age of The Sun
If sun gets its heat from burning or other chemical reactions, could only last 10,000 years or so.
Best 19th century guess: sun was slowly contracting.
Problem: only 30 million years ago, sun would have extended out to earth's orbit!
Geologists wanted more time, but you can't fight the laws of physics...
Sun actually gets its energy from nuclear reactions and can keep going for billions of years
The Geologists were right after all. Go Team.

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

32. Radiometric Dating: Half-Life

33. Present Radiometric Dating Methods
Cosmogenic
C Yr.
Primordial
K-Ar (K-40) 1.25 B.Y.
Rb-Sr (Rb-87) 48.8 by
U M.Y.

34. The Geologic Time Scale

35. 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.
Uplift of White Mtns. (N.H.) Granites
8 km/150 m.y. = 1 cm/190 yr.

36. 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.
Deposition of Niagara Dolomite
100 m/ 1 m.y.? = 1 cm/100 yr.

37. 1 Second = 1 Year 35 minutes to birth of Christ 1 hour+ to pyramids
3 hours to retreat of glaciers from Wisconsin
12 days = 1 million years
2 years to extinction of dinosaurs
14 years to age of Niagara Escarpment
31 years = 1 billion years

38. Were The Dinosaurs Failures?
Dinosaurs: 150,000,000 years
Recorded History: 5000 years
For every year of recorded history, the dinosaurs had 30,000 years
For every day of recorded history, the dinosaurs had 82 years
For every minute of recorded history, the dinosaurs had three weeks