1. Geologic Time

2. History Archbishop James Ussher 1581-1656
Studied writings and the bible
Calculated age of the Earth
Earth ~4000 years old
Created around 6 pm on Sunday, October 22, 4004 bc

3. History
Catastrophism
Changes happen quickly

4. History James Hutton (1726–1797) Father of modern geology
Watched erosion and sediments in a stream—took a long time to happen
Earth is much older
Uniformitarianism – 
Present is the key to the Past
Things that are happening now also happened in the past.

5. History Most modern geologists Combination of both Earth is very old
Changes happen very slowly 
Formation of layers
Weathering and erosion
Some catastrophic events occur quickly
Earthquakes, volcanoes, meteors, etc.

8. Law of Superposition
Bottom = older
Top = younger

9. Law of Horizontality Layers form horizontally
If not horizontal, assume they have been tipped.

10. Law of Cross Cutting Relationships
If a feature cuts across another feature, then that feature must be younger.

11. Law of Inclusions
An included rock is older than the rock around it.

12. Sedimentary Structures
Stratification - bedded or layered
 a. Different kinds of stratification (layers look different) are different environments of sedimentation. 

13. Unconformities Break in the Geologic Record
Sometimes means missing information
Angular Unconformity
Non-conformity
Dis-conformity (miss)

14. Angular Unconformity
Sedimentary layers deposited horizontally, tilted upward, eroded back to level, more layers deposited on top.
Lower layer meets upper layer at an angle

15. Development of an angular unconfomity

16. Angular Unconformity

17. Nonconformity
Igneous/Metamorphic rocks form, pushed to surface, erosion, sedimentary rocks deposited.

18. Disconformity
Sedimentary layers deposited horizontally, deposition stops, erosion, deposition resumes.
Loss of layers = loss of time

19. Fossil Succession
Fossil organisms succeed one another in a defined pattern.
We know which came first, etc.

20. Geologic Time There are two ways of dating geological materials.
Relative Age – This rock is older or younger than that rock.
(you are older or younger than a sibling)
Absolute Age –this rock is 3.2 million years old

21. Relative Ages Law of Superposition Law of Original Horizontality
Fossil Succession
Crosscutting Relationships

22. The geologic time scale – Earth’s “calendar” of
history.
Subdivides geologic history into units.
Originally created using relative dates.
Divisions are made when a major event started or ended
Structure of the geologic time scale
Eon – The greatest expanse of time (1000s of Ma).
Era – subdivision of an eon (100s of Ma)
Periods 
Epoch