1. Chapter 16- The Rock & Fossil Record
8th Grade Science
Chapter 16- The Rock & Fossil Record
© Fall 2005, Pflugerville ISD, 8th Grade

2. Chapter 16- The Rock & Fossil Record
Section 1: Earth’s Story & Those Who First Listened
Section 2: When on Earth?
Section 3: Looking at Fossils
Section 4: Time Marches On
Unit 4 : Chapter 16

3. “The present is the key to the past.” -James Hutton
What Do You Think?
We study the past because if we don’t, we are doomed to repeat it. But how can studying the present help us understand earth’s history?
What are some processes you can see today that also occurred millions of years ago?
Unit 4 : Chapter 16 : Section 1

4. Earth’s Story & Those Who Listened
“The present is the key to the past.”
Father of modern geology
James Hutton
Unit 4 : Chapter 16 : Section 1

5. Earth’s Story & Those Who Listened
Hutton knew that Hadrian’s wall was built by the Romans in historical times
Hadrian’s Wall, England
Unit 4 : Chapter 16 : Section 1

6. Earth’s Story & Those Who Listened
Only 1600 years old, the wall was already starting to weather and erode
Hadrian’s Wall, England
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7. Earth’s Story & Those Who Listened
Hutton wondered how long it would take to erode a mountain
Arthur’s Seat Volcano, Edinburgh, Scotland
Unit 4 : Chapter 16 : Section 1

8. Earth’s Story & Those Who Listened
Hutton decided that it would take millions of years, making the earth very ancient
Arthur’s Seat Volcano, Edinburgh, Scotland
Unit 4 : Chapter 16 : Section 1

9. Earth’s Story & Those Who Listened
Hutton realized that erosion and deposition have been going on for a long time
Arthur’s Seat Volcano, Edinburgh, Scotland
Unit 4 : Chapter 16 : Section 1

10. Earth’s Story & Those Who Listened
Uniformitarianism is Hutton’s belief that geologic processes are uniform and do not change over time
James Hutton
Unit 4 : Chapter 16 : Section 1

11. Earth’s Story & Those Who Listened
Hutton’s views of a billion-year-old earth clashed with most scientists’ belief in catastrophism
James Hutton
Unit 4 : Chapter 16 : Section 1

12. Earth’s Story & Those Who Listened
Most scientists supported catastrophism, the idea that all geologic change happens quickly
Unit 4 : Chapter 16 : Section 1

13. Earth’s Story & Those Who Listened
These scientists used huge floods, eruptions and catastrophes to explain rapid geologic change
Unit 4 : Chapter 16 : Section 1

14. Earth’s Story & Those Who Listened
Today, scientists think that sudden events are the cause of some changes in earth’s past
Unit 4 : Chapter 16 : Section 1

15. Earth’s Story & Those Who Listened
But they agree that the earth is billions of years old, and that most change is gradual
Unit 4 : Chapter 16 : Section 1

16. When on Earth? What Do You Think?
Suppose your friend piles his stuff on his floor and never cleans his room. Under the top layer of clothes, you find a pizza box. Under this is a bunch of CDs then some homework and under this is a ham sandwich.
Arrange these four layers from oldest to youngest…
Unit 4 : Chapter 16 : Section 2

17. Unit 4 : Chapter 16 : Section 2
When on Earth?
The Principle of Superposition states that younger rocks lie over older rocks
Grand Canyon
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18. Unit 4 : Chapter 16 : Section 2
When on Earth?
The Principle of Superposition is used to find the relative ages of rock layers
Grand Canyon
Unit 4 : Chapter 16 : Section 2

19. Unit 4 : Chapter 16 : Section 2
When on Earth?
The Law of Cross-Cutting Relationships can tell geologists the relative age of a fault or intrusion
Unit 4 : Chapter 16 : Section 2

20. Unit 4 : Chapter 16 : Section 2
When on Earth?
The dike is the youngest feature, because the other layers were cut by it
Unit 4 : Chapter 16 : Section 2

21. Unit 4 : Chapter 16 : Section 2
Relative Dating
Use your knowledge to order the layers, faults and intrusions in the next slide from oldest to youngest
Unit 4 : Chapter 16 : Section 2

22. Unit 4 : Chapter 16 : Section 2
Relative Dating
Unit 4 : Chapter 16 : Section 2

23. Unit 4 : Chapter 16 : Section 1
Relative Dating
Geologists can use rock layers from many locations to create a geologic column
James Hutton
Unit 4 : Chapter 16 : Section 1

24. Unit 4 : Chapter 16 : Section 2
Relative Dating
Unit 4 : Chapter 16 : Section 2

25. Unit 4 : Chapter 16 : Section 2
Relative Dating
The geologic column is an ideal sequence of rock layers that contains all known rock formations and fossils on Earth
Unit 4 : Chapter 16 : Section 2

26. Unit 4 : Chapter 16 : Section 2
When on Earth?
An unconformity is a surface that represents a missing part of the geologic column
Hutton’s Unconformity
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27. Formation of an Unconformity
Sediment is eroded from a hill and deposited in a valley
30-15 Million Years Ago
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28. Formation of an Unconformity
The area is uplifted and exposed to erosion, then the land surface is eroded away
15-5 Million Years Ago
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29. Formation of an Unconformity
Deposition resumes
Can you spot the unconformity?
5 Million Years Ago- Present
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30. Unit 4 : Chapter 16 : Section 2
Absolute Dating
When animals eat, they ingest radioactive Carbon-14
Unit 4 : Chapter 16 : Section 2

31. Unit 4 : Chapter 16 : Section 2
Absolute Dating
Nitrogen-14
Carbon-14
Carbon-14 decays into Nitrogen-14
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32. Unit 4 : Chapter 16 : Section 2
Absolute Dating
By comparing the amount of C-14 to N-14, geologists can calculate the age of a fossil
Unit 4 : Chapter 16 : Section 2

33. Unit 4 : Chapter 16 : Section 2
Absolute Dating
Since C-14 has a half-life of only 5730 years, other isotopes are used to date older rocks
Unit 4 : Chapter 16 : Section 2

34. Unit 4 : Chapter 16 : Section 1
Absolute Dating
The oldest rocks on Earth have been dated to 4.5 billion years, confirming Hutton’s beliefs
James Hutton
Unit 4 : Chapter 16 : Section 1

35. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
What Do You Think?
Imagine that a geologist 65 million years from now has unearthed fossils of your life. What would she find?
Unit 4 : Chapter 16 : Section 3

36. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
A fossil is the remains or physical evidence of an organism preserved by geologic processes
Saber-Tooth Cat Fossil
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37. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Fossilized tree sap is called amber
Fossil Amber with Insect Inclusions
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38. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Animals caught in amber are perfectly preserved
Fossil Amber with Insect Inclusions
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39. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Fossils of mammoths, extinct for 12,000 years, have been found frozen in Arctic ice
Woolly Mammoth
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40. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
A trace fossil is naturally preserved evidence of animal activity
Theropod Track
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41. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
This dinosaur track is located in Glen Rose, Texas, in Dinosaur Valley State Park
Theropod Track
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42. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
A mold is a cavity in rock where a plant or animal was buried
Ammonite Fossil
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43. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
A cast is an object made when sediment fills a mold and becomes rock
Ammonite Fossil
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44. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Unit 4 : Chapter 16 : Section 3

45. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Which of these is the mold and which is the cast?
Ammonite Fossil
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46. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
Most animals are not buried fast enough to form fossils
Whale Bones
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47. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
These whale bones will be broken down before they can form fossils
Whale Bones
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48. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
The trilobite Phacops lived for a short time 400 million years ago
Trilobite Fossil
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49. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
An index fossil is one found for a short time in rock layers around the world
Trilobite Fossil
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50. Unit 4 : Chapter 16 : Section 3
Looking at Fossils
If Phacops is found in a rock layer, the rock must be about 400 million years old
Trilobite Fossil
Unit 4 : Chapter 16 : Section 3

51. Unit 4 : Chapter 16 : Section 4
Time Marches On
What Do You Think?
If the history of Earth were the length of one calendar year, on what date do you think modern humans arrived?
Unit 4 : Chapter 16 : Section 4

52. Unit 4 : Chapter 16 : Section 4
Time Marches On
Humans evolved in the last half-hour of New Years Eve!
Humans First Arrived
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53. Unit 4 : Chapter 16 : Section 4
Time Marches On
The Geologic Time Scale divides Earth’s history into eons, eras, & periods
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54. Unit 4 : Chapter 16 : Section 4
Time Marches On
Since most fossils are from the Phanerozoic Eon, this is the eon that is given the most attention
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55. Unit 4 : Chapter 16 : Section 4
Time Marches On
The Phanerozoic is actually the shortest of the four eons
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56. Unit 4 : Chapter 16 : Section 4
Time Marches On
In the Paleozoic Era, life in the oceans, as well as all major plant groups, flourished
Paleozoic Era mya
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57. Unit 4 : Chapter 16 : Section 4
Time Marches On
With a mass extinction at the end of the Paleozoic, the remaining reptiles thrived
Mesozoic Era mya
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58. Unit 4 : Chapter 16 : Section 4
Time Marches On
Known as the Age of Reptiles, birds and small mammals appeared late in the Mesozoic
Mesozoic Era mya
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59. Unit 4 : Chapter 16 : Section 4
Time Marches On
Mammals flourished after a mass extinction killed the dinosaurs
Cenozoic Era 65 mya- Present
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60. Unit 4 : Chapter 16 : Section 4
Time Marches On
The Cenozoic is known as the Age of Mammals
Cenozoic Era 65 mya- Present
Unit 4 : Chapter 16 : Section 4

61. Let’s Review!
- 1 -
What did James Hutton mean by the comment, “The present is the key to the past”?
Unit 4 : Chapter 16

62. How can you tell the age of rocks and fossils?
Let’s Review!
- 2 -
How can you tell the age of rocks and fossils?
Unit 4 : Chapter 16

63. Describe how a geologist would use an index fossil…
Let’s Review!
- 3 -
How is a fossil created?
Describe how a geologist would use an index fossil…
Unit 4 : Chapter 16

64. What type of event ended both the Paleozoic and Mesozoic Eras?
Let’s Review!
- 4 -
What type of event ended both the Paleozoic and Mesozoic Eras?
What geologic time period was occurring 200 million years ago?
Unit 4 : Chapter 16

65. Web Sites to Visit: .
Unit 4 : Chapter 16

66. Pre-AP Extensions
Unit 4 : Chapter 16