1. DO NOW: Discuss with your table: Where in this picture would you expect to find the OLDEST rocks? Where would you expect to find the NEWEST rocks? What kinds of events might change that?

2. Chapter 3 The Rock and Fossil Record
Section 1: Earth’s Story and Those Who Listened

4. The Rock and Fossil Record
Geology- Study of Earth’s history

5. Paleontology
The science of studying fossils to learn about past life on Earth.

6. How does Earth Change?
Most changes on the Earth are slow – erosion, deposition, pressure, melting.
Some changes are quick – volcanos, earthquakes, asteroid impacts,

7. Chapter 3 The Rock and Fossil Record
Section 2: Relative Dating: Which Came First?

8. Relative Dating
Finding an estimated age of objects on Earth by comparing it with rocks and fossils.

9. The Law of Superposition
Superposition - Fossils/Rocks closer to Earth’s surface will be younger than Fossils/Rocks found closer to Earth’s center.

11. Disturbing Forces The law of superposition does not always hold true!
Sometimes there are disturbing forces that cause rocks to tilt, fold, or get flipped upside down.
This can be due to:
Earthquakes
Magma intrusions
Folding or tilting of rock layers

12. Law of Crosscutting Relationships
Any rock layer that cuts across any other rock layer is younger than the one it cuts across.
What can cut across a rock layer?
Intrusions – magma can seep in between rocks and then harden to intrusive igneous rock
Faults – cracks in rocks along which the rocks move
F, A, and C are older than B
E is older than B

15. Disturbed Rock Layers
1.) Fault- A break in Earth’s crust, that force the crusts to slide opposite of each other.
2.) Intrusion- Molten rock pushes up between existing rock layers.

16. Disturbed Rock Layers
3.) Folding- When Earth’s layers bend and buckle from internal forces such as tectonic plates
4.) Tilting- Internal forces slant rock layers instead of folding them.

17. Disturbed Rock Layers
All of these disturbances are younger than the rock layers they affect!
The rock layers had to have been there already for the change to take place.

18. 6
What is the story here?

19. What is the story here?

20. What is the story here?

21. The Geologic Column
A collection of undisturbed fossil/rock layers from all over the world with oldest rocks at the bottom.
An “IDEAL” picture of what rocks would be present if there had been no disturbing forces.
Geologists use it to compare to other rock sequences and find out what’s missing.

22. Pd 1

23. Index Fossils
Index fossils are fossils of organisms that lived for a short period of time all over the world.
If you find an index fossil in a piece of rock, you know how old that rock is.

24. Common Index Fossils
Trilobites are fossils that are found in the MAUV LIMESTONE layer of the Grand Canyon. Trilobites are known to have only existed on Earth 543 to 505 million years ago, so the Mauv Limestone must be million years old!

25. This layer of Bryce Canyon is called the Winsor Layer
This layer of Bryce Canyon is called the Winsor Layer. It contains fossils of cephalopods which were only on Earth from 199 to 145 million years ago. So, the Winsor Layer is million years old.

26. Missing Pieces of the Record
Missing rock layers create gaps in rock layer sequences called unconformities.
Unconformity - a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

27. 3 Types of Unconformities:
Disconformity
Nonconformity
Angular unconformity

28. 3 Types of Unconformities
1.) Disconformity- Sequence of parallel rock is missing! It is hard to see but very common.

29. Disconformity

30. 3 Types of Unconformities
2.) Nonconformity - Sedimentary rock layers lie on top of an eroded surface of a non-layered igneous or metamorphic rock.
Layers are on top of non-layered rock

31. Nonconformity

32. 3 Types of Unconformities
3.) Angular Unconformity - exists between horizontal rock layers and eroded tilted or folded rock layers.
The tilted or folded layers were eroded before horizontal layers formed above them.

33. Angular Unconformity

34. Angular Unconformity

35. 5
What is the story here?

38. Chapter 3 The Rock and Fossil Record
Section 3: Absolute Dating: A Measure of Time

39. Absolute Dating
Absolute Dating -A very accurate way of dating and measuring the age of rocks and fossils.
Geologists do this by using Isotopes and Radioactive Decay

40. Isotopes Isotopes are unstable forms of elements.
They change, at a predictable pace, into stable forms of the elements.
Some isotopes change quickly and some change slowly.
When the isotope changes, it’s called radioactive decay.

41. Radioactive Decay An unstable atom turns into a stable atom.
Unstable = parent
Stable = daughter

42. Radioactive Decay
Because radioactive decay occurs at a steady pace, scientists can use the relative amounts of stable daughter and unstable parent atoms present in an object to determine the object’s age.

43. Radiometric Dating
Using radioactive decay to determine how old a rock is
Scientists determine a ratio of the unstable isotope is present compared to how much of the stable isotope is present.

45. In other words….
An element changes forms over time helping scientist accurately date things

46. Half Life
The amount of time it takes for one half of the parent isotope to turn into daughter isotope
Newly formed rock = 100% parent
After 1 half life = 50% parent

48. The element we measured has a half life of 10,000 years.
EXAMPLE
The element we measured has a half life of 10,000 years.
This rock is two half lives old because ¾ of it has changed to daughter. The rock is 20,000 years old.
This rock is three half lives old because 7/8 of it has changed to daughter. The rock is 30,000 years old.
This rock is four half lives old because 15/16 of it has changed to daughter. The rock is 40,000 years old.
This rock is newly formed
This rock is one half life old because half of it has changed to daughter. The rock is 10,000 years old.

49. Example The half life of the element we measured is 8 years.
If ¼ of your sample is parent material then ______ is daughter material.
If ¼ of the your sample is parent material, how many half lives has it been through?
3/4 2

50. Example The half life of the element we measured is 2000 years.
If 1/16 of your sample is parent material then how many half lives has it been through? ___________
How old is it? ______________ 4
4 x 2000 = 8000 years

51. Example
If the mineral you’re studying has a half life of 12,000 years, identify the fraction of parent and daughter isotopes and the ages of each of these rock samples.

52. Examples of Elements used in Radiometric Dating
Uranium decays to lead-206
1/2 life is 4.5 billion years
Potassium 40- decays to Argon and Calcium
1/2 life of 100,000 years
Carbon-14 -decays to carbon-12
1/2 life of 5,000 years

53. The Rock and Fossil Record Section 4: Looking At Fossils
Chapter 3
The Rock and Fossil Record
Section 4: Looking At Fossils

54. Fossils Any naturally preserved evidence of life.
Fossils can indicated changes in the environment and can give us a time frame for the life span of certain plants and animals

55. Fossilization
Formation of fossils

56. 1. Mummification
In dry areas organisms can die and be preserved because of low humidity and most bacteria can not survive in these places.

61. 2. Preservation in Amber Amber is hardened tree sap
Amber traps insects and preserves them

66. 3. Tar Seeps/Tar Pits
Thick petroleum oozes to Earth’s surface and traps animals
You can see the fossils of ice age animals from 10,000 to 40,000 years old, such as a saber tooth Tiger

67. Found in LaBrea Tar Pits near Los Angeles

69. 4.) Freezing
Low temperatures protect and preserve organisms and keep bacteria out

72. 5.) Petrification Minerals replace an organism’s tissues.
Petrified wood is actually stone and fossilized.

73. Petrified Wood- It is all made of minerals now

78. 6.) Imprints
Made in soft mud or clay and preserved in sedimentary rock.

89. 7.) Casts
Formed when sediments fill an imprint (mold) and then cement to form rocks with the reverse impression of the organism

94. 8.) Coprolites
Fossilized waste materials

96. 9.) Gastroliths
Fossilized stones from inside an organism’s digestive system to help break food into smaller parts.
The stones become gastroliths when the organism is dead

97. Pleiosaur Gastroliths

99. The Rock and Fossil Record Section 5 – Time Marches On
Chapter 3
The Rock and Fossil Record
Section 5 – Time Marches On

100. Geologic Time Scale
Divides Earth’s 4.6 billion year history into time intervals (4 Eons)

101. Divisions of Time
Eons Eras  Periods Epochs
Biggest Smallest

102. What Determines a New Era?
The geologic column is divided into EONS, ERAS, PERIODS, & EPOCHS based on major changes in:
Earth’s surface
Climate
Type of organisms

103. The Phanerozoic Eon is all of the time that Earth has been here – 4
The Phanerozoic Eon is all of the time that Earth has been here – 4.6B years. It’s divided into:
Paleozoic Era – 251M-542M years ago
Mesozoic Era – 65M-251M years ago
Cenozoic Era – 65Myears ago to today
542MYA MYA MYA TODAY
Paleozoic Mesozoic Cenozoic

105. Paleozoic Era 542 to 251 million years ago
Begins - with dramatic increase in plant and animal species.
Ends - with landform called Pangaea and mass extinction of 90% marine species and 70% land species.

106. Pangea

107. Known as “Age of Reptiles” Pangaea breaks up
Mesozoic Era
251 to 65.5 million years ago
Known as “Age of Reptiles”
Ex. Dinosaurs
Pangaea breaks up

108. Cenozoic Era
65.5 million years ago to present
“Age of Mammals”
Continents move to present day positions.