1. Geologic History
A new way to look at time

2. How Can Rocks Help? Been around for a long time
Record geologic history
Show changes in life forms
Does this give us a complete record of Earth’s history? NO
Crust is constantly recycled
Like a book with pages missing

3. Archbishop James Ussher
Created a timeline of human history
Related it to the history of the Earth
Earth created in 4004 BCE
He wasn’t right so why was he important?
Earth was over 5000 years old.
First person to make a timeline of Earth’s history

4. James Hutton Scottish physician “The key to the future is the past”
Uniformitarianism
Same processes happening now as historically
Shaped Earth over a long period of time
Not cataclysmic events (Catastrophism)
Gentleman farmer

5. Relative Dating Sequences events
Does not tell how long ago they happened
Uses rock layers
3 major laws (6 total)

6. Original Horizontality
Assumes rock layers were originally laid down horizontally.
Layers can be tilted or folded as time goes on so the more wiggles the older the rock

7. Law of Superposition IMPORTANT
Layers on the bottom are older than layers on the top

8. Law of Cross-Cutting Relationships
IMPORTANT
Anything that cuts through another layer is younger than the layers it cuts through
2 types of cross-cutters

9. Cross-Cutters Faults: Intrusions: Displace layers Go through layers
Faults are drawn as thin lines and you can see where the layers have been moved.
Intrusions are drawn as oddly shaped blobs. They “intrude” into the surrounding layers of rock.
Both can cut across the other.

10. Law of Included Fragments
IMPORTANT
AKA inclusions
Fragments in the rock are always older than the rock itself
Pieces of rock from below found in layers of rock above

11. Unconformities Not a law, but important Shows a stop in deposition
Erosion surface
Irregular surface between layers
Associated with included fragments

12. Let’s Practice… E G L C H M D J A N K B f
Fix f to F
Fix animation on B
Unconformities between E and G, C and M, D and N, and F and B

13. Correlation of Rock Layers
Rock layers in different places can be matched up
Gives more information
Must be near each other
Carmel Formation and Navajo Sandstone
Moenkopi Formation and Kaibab Limestone
Missing second circle.

14. Radioactive Dating AKA Radiometric Dating or Numerical Dating
Tells how old something is
Uses radioactive isotopes
Compare and contrast with relative dating.

15. Parent and Daughter Parent material: Daughter material:
Radioactive or unstable
Original material
Daughter material:
Non-radioactive or stable
Altered or new material
Parent material decays (or changes) into daughter material

16. Half-Life Expresses the rate of radiometric decay
How long it takes for half of the parent material to turn into daughter material

17. How’s it Work? Uses known rates of decay
Compare the ratio of parent material to daughter material
Match it with the known rates of decay

18. Common Radioactive Isotopes
Parent
Daughter
Half-Life
(in years)
Uranium-235
Lead-206
4.5 billion
Uranium-238
Lead-207
713 million
Thorium-232
Lead-208
14.1 billion
Rubidium-87
Strontium-87
47.0 billion
Potassium-40
Argon-40
1.3 billion

19. Tree Rings Count the rings to find the tree’s age Can show:
Rainy seasons
Dry seasons
Problems like ash fall and forest fires

20. Varves Only form on the bottom of lakes
Count the layers to find how old the lake was
Two layers means one year

21. Geologic Timescale Broken into eons, eras, and periods
Eons are the largest
Periods are the smallest
Periods are sometimes broken into epochs (but only recently)

22. Eons and Eras Eons: Eras: Phanerozoic: Precambrian: Paleozoic:
“visible life”
What does this mean?
Precambrian:
88%
Why isn’t it divided?
Eras:
Paleozoic:
“early life”
Mesozoic:
“middle life”
Cenozoic:
“recent life”