1. Chapter 3- The Rock and Fossil Record

3. Study of Earth’s history
Geology
Study of
Earth’s history

4. Many Geologists had different theories about our changing Earth
2 Main Theories:
Uniformitarianism
Catastrophism

5. Uniformitarianism Developed by: James Hutton 1788
Stated that the key to understanding Earth’s history was all around us – the geologic processes that we observe today have always occurred.
Ex: erosion, climate change

6. Catastrophism
Principle that states that all geologic change occurs suddenly and rarely
Allows scientists to believe that the Earth isn’t as old as Hutton suggested
Ex: asteroid impacts, earthquakes, volcanic eruptions

7. Charles Lyell 1830s Challenged principle of catastrophism
No evidence of catastrophes, obvious evidence of uniformitarianism

8. Uniformitarianism Wins!!
The 2 scientists who finally convinced the public of uniformitarianism were:
James Hutton
Charles Lyell
James Hutton
Charles Lyell

9. Extinction of Dinosaurs
Even though Uniformitarianism is the main belief how earth changes, it does not rule out that some events in Earth’s history were caused by catastrophes.

10. Extinction of the Dinosaurs
Example
Extinction of the Dinosaurs
A big asteroid was thought to have struck the Earth with such force, causing dirt to completely block sun-light changing the climate to inhabitable for plant and animal life.

11. Paleontology
Science of studying fossils to learn about past life on Earth

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

13. Superposition
Fossils/Rocks closer to Earth’s surface will be younger than Fossils/Rocks found closer to Earth’s center.

15. Disturbing Forces
The law of superposition only holds true IF there have been no disturbing forces such as:
Earthquakes
Magma intrusions
Folding or tilting of rock layers

17. The Geologic Column
A collection of Fossil/Rock sequences from all over the world
Geologists use the geologic column to compare to other rock sequences.
This can help geologist determine the age and other information about a certain area.

19. Disturbed Rock Layers
Faults- A break in Earth’s crust, that force the crusts to slide opposite of each other.
Intrusion- Molten rock (from metamorphic stage) pushes up between existing rock layers.

20. Folding- When Earth’s layers bend and buckle from internal forces such as tectonic plates
Tilting- Internal forces slant rock layers instead of folding them.

21. 6
What is the story here?

22. 8
What is the story here?

23. Law of Cross-Cutting Relationships
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

24. 11
What is the story here?

25. Missing Pieces of the Record
Missing rock layers create gaps in rock layer sequences called unconformities.

26. 3 Types of Unconformities:
Disconformity
Nonconformity
Angular unconformity

27. Disconformity- Sequence of parallel rock is missing- hard to see but very common

29. 1
What is the story here?

30. 2
What is the story here?

31. Nonconformity- Sedimentary rock layers lie on top of an eroded surface on non-layered igneous rock or metamorphic rock. (layers on top of non-layered rock)

33. Angular Unconformity- Exists between horizontal rock layers and eroded tilted/folded rock layers. The tilted or folded layers were eroded before horizontal layers formed above them.

36. 5
What is the story here?

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

40. Radioactive Decay
An unstable atom turns into a stable atom . When this happens, electrons are released.

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

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

44. Radiometric Dating
Method of using radioactive decay to determine how old a rock is.
Ratio of parent to daughter material or unstable to stable isotopes found.

45. Ex: Say it takes 10,000 yrs for parent material in a rock to decay…
Ex: Say it takes 10,000 yrs for parent material in a rock to decay….and you find equal amounts of parent material and daughter material in the sample… This means that ½ of the original material has decayed making the rock 10,000 years old. (1/2 life)

47. Half-life
If ¼ of your sample is parent material and ¾ is daughter material and you know that it takes 10,000 years to decay ½ of the original sample, how old is the rock?
20,000 years old because 10,000 decayed twice is
10,000 x 2 = 20,000
1 half life is 10,000….2 half-lives is 20,000…..3 half-lives is 30,000.

48. Elements used in Radiometric Dating
Uranium-238 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 with a ½ of 5,000 years
** In a rock carved village that was said to have been built 2, years ago, which type of radiometric dating would you use to investigate the burial mounds?

49. Fossils
A fossil is any naturally preserved evidence of life. You can find fossils in:
Rocks
Amber
Ice
Tar

50. Fossils can:
indicate changes in the environment
give us a time frame for the life span of certain plants and animals (index fossils are used) ex. Phacops lived in shallow oceans YRS ago

51. Fossilization
Formation of fossils

52. 1. Mummification
Found in dry places because most bacteria can not survive in these places

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

62. 3. Tar Seeps/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

63. Found in LaBrea Tar Pits near Los Angeles

65. 4 - Freezing
Low temperatures protect and preserve organisms and keep out bacteria

68. 5 - Petrification
Mineral solutions replace organic materials

69. Permineralization- when minerals fill in pore space of an organism’s tissues and is preserved
Petrification- When the organism is completely replaced by minerals (petrified wood is actually stone)

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

75. 6 - Imprints
Made in soft mud or clay and preserved in sedimentary rock

86. 7 – Molds and Casts
Formed when sediments fill an imprint and then cement to form rocks with the reverse impression of the organism

91. 8 - Coprolites
Fossilized waste materials

93. 9 - Gastroliths Some animals have stones in their digestive system
These stones help them break their food into smaller parts
The stones become gastroliths when the organism is dead

94. Pleiosaur Gastroliths

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

97. What Determines a New Era?
The geologic column is divided into EONS, ERAS, PERIODS, PERIODS, and EPOCHS based on:
Major changes in Earth’s surface
Major changes in climate
Major changes in the type of organisms

98. Divisions of Time
Eons
Eras
Periods
Epochs

99. Hadean Era = PreCambrian Time
Begins with formation of Earth
Ends about 542 Ma (‘mega annum = 1M years)
88% of Earth’s history
Blue-green algae, marine worms, jellyfish, single celled organisms

100. Paleozoic Era
542 Ma to 251 Ma
Begins with dramatic increase in plant and animal species
Ends with Pangaea
Divided into 7 periods
Cambrian
Ordovician
Silurian
Devonian
Mississippian Carboniferous
Pennsylvanian Carboniferous
Permian
Ends with 90% marine and 70% land extinction

101. Mesozoic Era
251 Ma to 65.5 Ma
Pangaea breaks up, Sierra Nevada and Andes form
“Age of Reptiles”
3 periods:
Triassic
Jurassic
Cretaceous
Ends with mass extinction – KT Boundary

102. Cenozoic Era 65.5 Ma to present
Continents move to present day positions
Alps, Himalayas form
“Age of Mammals”
2 periods:
Tertiary
Quaternary

103. Tertiary Period 65.5 Ma to 1.8 Ma Begins at KT Boundary
Ends at last Ice Age
5 epochs:
Paleocene
Eocene
Oligocene
Miocene
Pliocene

104. Quaternary Period 1.8 Ma to present Begins with last Ice Age 2 epochs:
Pleistocene
Holocene

105. Holocene Epoch
Began 11,500 years ago
Modern humans

107. Earth’s Clock
If Earth was 12 hours old, 1 hour=383million years, 1 minute= 6.4 million years and 1 second = 106,000 years!!! In the scheme of things, a human life span would be less than an eye blink long!!!!!