1. Chapter 17 The Rock Record
Page 322

2. BELLWORK: Order the following rock layers from oldest  youngest

4. How old is the Earth????? 4.6 billion years old How do we know???
By the geologic record

5. §17-1 Determining Relative Age
Objectives:
State the principle of uniformitarianism.
Explain how the law of superposition can be used to determine the relative age of rocks.
Compare the 3 types of unconformity.
Apply the law of crosscutting relationships to determine the relative age of rocks.

6. Uniformitarianism
originated with Scottish geologist James Hutton in 1785
history could be interpreted in terms of processes currently observed.
For example, he suggested that deep soil profiles were formed by the weathering of bedrock over thousands of years.

7. Relative Dating of Rocks
In sedimentary rocks, Age is based on position
“Law of Superposition”

8. Law of Superposition

9. Unconformities Gaps in the geologic record. Periods of erosion
Unknown time of creation.

10. Nonconformity igneous intrusions into the sedimentary rock layers.
When was it created??
igneous intrusions into the sedimentary rock layers.

13. Disconformity
Hard to recognize because all layers are horizontal.

14. Cross-Cutting Relationships
Anything which deforms or cuts across a rock is younger than the rock itself

15. Here are some real life examples of cross-cutting relationships:

17. §17-2 “Determining Absolute Age”
Objectives:
Summarize the limitations of using the rates of erosion and deposition to determine the absolute age of rocks.
Describe the formation of varves.
Explain how the process of radioactive decay can be used to determine the absolute age of rocks.

18. Relative Age = little sister, big brother, mom & granddad
Absolute age =>
Little sister is 2 Years old
Big brother is 6 years old
Mom is 30 years old
Granddad is 65 years old

19. Relative Age based on Rates of Erosion
Only works for the past 10-20,000 years.
Example:
Niagara Falls is 9900 years old based on current erosion of the edge of 1.3 m per year

20. Relative Age based on rates of deposition
30 cm every 1000 years for sedimentary rock
BUT if there is a flood or other event this is not very accurate.

21. Varve Count Varve = yearly layers of sediment
A lot like counting tree rings.
Each year has:
a light colored, course layer of sediment &
a dark,fine layer of sediment.

22. Dating using Radioactive Decay
Uranium- 238 is the most widely used element.
It breaks down at a predictable rate to Lead-206:
½ every 4.5 billion years

25. Gizmo on Radioactive Decay
Activity today is:
Gizmo on Radioactive Decay
Explorelearning.com

26. §17-3 The Fossil Record Objectives:
Describe 4 ways in which entire organisms can be preserved as fossils.
List 4 examples of fossilized traces of organisms.
Describe how index fossils can be used to determine the age of rocks.

27. Paleontologists – study fossils
Fossils can only be found in sedimentary rock

28. SO HOW DOES AN ANIMAL BECOME A FOSSIL?
                           
                                
                              
Millions of years later sand hardens to rock and the shell or its imprint is preserved as a fossil.
Illustrations: M. Leverock.

29. Preservation is the Key !!
Remains Instantly Covered by
Mud
Sand
Silt/clay
Other organisms

30. Mummification
Occurs in deserts

31. Amber = pine sap
Actually preserves insects perfectly including the DNA
This is how the scientists created the dinosaurs in the movie “Jurassic Park”!!

32. Tar Seeps
Like the La Brea Tar Pits in California.

33. Freezing
Like “Ice Man” & the mammoth found in Siberia.
                                                                  

34. Petrification
Example:
The Petrified Forest in Arizona

35. Trace Fossils
3D imprints are called “molds”

36. Very Gross trace fossils
Coprolites
Fossilized poop
Show scientists what the animals ate.
Gastroliths
Stomach Stones used by dinosaurs to grind their food
Like birds do today.

37. Interpreting the fossil record
Used to date rocks
How environments have changed
Remember Wegener?
How animals were affected & adapted to the environment
Remember Darwin?

38. Index Fossils Example: Trilobites
Formed from organisms that were widespread but only lived for a short period of geologic time
Example: Trilobites