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. Ripple Marks, Bay Beach

4. Fossil Ripple Marks, Baraboo Range

5. Modern Mud Cracks

6. Fossil Mud Cracks, Virginia

7. 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 1861-1865 World War II 1939-1945 Glaciers Left Wisconsin About 11,000 Years Ago

8. Superposition: Mindoro Cut, Wisconsin

9. Geologic Map

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

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

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

13. 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

14. Dinosaur Tracks, Texas

15. Rubbing Rock? Wisconsin

16. Rubbing Rock? California

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

18. Pseudofossils

19. Johannes Beringer’s “Fossils”

20. 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

21. Fossil Tree in Lava Flow, Hawaii

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

23. Correlation

24. The Geologic Time Scale QuaternaryLatin, “fourth”1822 TertiaryLatin, “third”1760 CretaceousLatin creta, “chalk”1822 JurassicJura Mountains, Switzerland1795 TriassicLatin, “three-fold”1834 PermianPerm, Russia1841 CarboniferousCarbon-bearing1822 DevonianDevonshire, England1840 SilurianSilures, a pre-Roman tribe1835 OrdovicianOrdovices, a pre-Roman tribe1879 CambrianLatin Cambria, “Wales”1835

25. Absolute Ages: Early Attempts The Bible Add up Dates in Bible Get an Age of 4000-6000 B.C. For Earth John Lightfoot and Bishop Ussher - 4004 B.C. (1584) Too Short

26. 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

27. 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.

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

29. Radiometric Dating: Half-Life

30. Present Radiometric Dating Methods Cosmogenic C-14 5700 Yr. Primordial K-Ar (K-40) 1.25 B.Y. Rb-Sr (Rb-87) 48.8 by U-235 704 M.Y.

31. The Geologic Time Scale

32. 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.

33. 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.