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. Law of Superposition When Rock is deposited in layers
the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it. 

11. Geologic Map

12. What is a fossil? What do fossils tell us?
A fossil is the preserved remains of a once- living organism.
What do fossils tell us?
Fossils give clues about organisms that lived long ago. They help to show that evolution has occurred.
They also provide evidence about how Earth’s surface has changed over time.
Fossils help scientists understand what past environments may have been like.

13. HOW IS A FOSSIL FORMED? 1. Sediment 2. Layers 3. Movement 4. Erosion
An animal is buried by sediment, such as volcanic ash or silt, shortly after it dies. Its bones are protected from rotting by the layer of sediment.
2. Layers
More sediment layers accumulate above the animal’s remains, and minerals, such as silica (a compound of silicon and oxygen), slowly replace the calcium phosphate in the bones.
3. Movement
Movement of tectonic plates, or giant rock slabs that make up Earth’s surface, lifts up the sediments and pushes the fossil closer to the surface.
4. Erosion
Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.

14. Dinosaur Tracks, Texas

15. Rubbing Rock? Wisconsin

16. Rubbing Rock? California

17. Pseudofossils Look Like Fossils But Aren't
Dendrites- Dendrites are delicately branched deposits of black minerals (typically manganese oxides) that have been precipitated from water seeping through fractures in fine-grained rocks.
Concretions-
A concretion is a compact aggregate of mineral matter found in a host rock which usually has a different composition. Most concretions are roughly spherical, but they can also be cylindrical, disc-shaped or irregular, perhaps even resembling a fossilised animal part, such as a limb bone or skull.

18. Pseudofossils (Dendrite)

19. Natural or Sculpture?

20. Johannes Beringer’s “Fossils”

21. Beringer’s Book

22. FIVE MAIN TYPES OF FOSSILS
Petrified
Fossils
Molds and
Casts
Carbon Films
Trace
Fossils
Preserved
Remains

23. PETRIFIED FOSSILS The word “petrified” means “turning into stone.”
PETRIFIED FOSSIL The Field Museum in Chicago displays a fossil of a Tyrannosaurus rex.
The word “petrified” means “turning into stone.”
Petrified fossils form when minerals replace all or part of an organism.
Water is full of dissolved minerals. It seeps through the layers of sediment to reach the dead organism. When the water evaporates, only the hardened minerals are left behind.

24. MOLDS AND CASTS MOLD FOSSIL
This mold, or imprint, is of an extinct mollusk called an ammonite.
A mold forms when hard parts of an organism are buried in sediment, such as sand, silt, or clay.
The hard parts completely dissolve over time, leaving behind a hollow area with the organism’s shape.
A cast forms as the result of a mold.
Water with dissolved minerals and sediment fills the mold’s empty spaces.
Minerals and sediment that are left in the mold make a cast.
A cast is the opposite of its mold.
CAST FOSSIL This ammonite cast was discovered in the United Kingdom.

25. CARBON FILMS
FERN FOSSIL This carbon-film fossil of a fern is more than 300 million years old.
All living things contain an element called carbon.
When an organism dies and is buried in sediment, the materials that make up the organism break down.
Eventually, only carbon remains.
The thin layer of carbon left behind can show an organism’s delicate parts, like leaves on a plant.

26. FANCY FOOTWORK This dinosaur footprint was found in Namibia, Africa.
TRACE FOSSILS
Trace fossils show the activities of organisms.
An animal makes a footprint when it steps in sand or mud.
Over time the footprint is buried in layers of sediment. Then, the sediment becomes solid rock.
FANCY FOOTWORK This dinosaur footprint was found in Namibia, Africa.

27. PRESERVED REMAINS
Some organisms get preserved in or close to their original states. Here are some ways that can happen.
Tar An organism, such as a mammoth, is trapped in a tar pit and dies. The tar soaks into its bones and stops the bones from decaying.
Ice An organism, such as a woolly mammoth, dies in a very cold region. Its body is frozen in ice, which preserves the organism—even its hair!
Amber An organism, such as an insect, is trapped in a tree’s sticky resin and dies. More resin covers it, sealing the insect inside. It hardens into amber.

28. 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

29. Fossil Tree in Lava Flow, Hawaii

30. Using Fossils to find the age?
Index Fossil
Law Of Superposition

31. Index Fossils
Using a known fossil age to date anything found in the same sediment layer

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

33. 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”

34. 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

35. 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

36. 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.

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

38. Radiometric Dating: Half-Life

39. 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.

40. The Geologic Time Scale

41. 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.

42. 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.

43. If 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

44. 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