1. Geologic Time
Earth’s History

2. Uniformitarianism The present is the key to the past
Processes that happen today are the same processes that happened in ancient times
Modern Mudcracks
Fossilized Ripples
Fossilized Mudcracks
Modern Ripples

3. Dating – 2 types Relative Dating Absolute Dating
Know order of events but not dates
Absolute Dating
Know exact age

4. Relative Dating – Key Concepts
Law of Superposition
Principle of Original Horizontality
Principle of Cross-Cutting Relationships
Principle of Inclusions

5. Law of Superposition
Each bed is younger than the bed below it.

6. Principle of Original Horizontality
Sedimentary layers are deposited horizontally

7. Principle of Cross-Cutting Relationships
Faults and intrusions are younger than the rocks they cut through

8. Inclusions
Fragments of one rock unit that have been enclosed within another are older

9. Relative Dating Youngest  G A B C F D Oldest  E
E is younger than D. Which Principle used?
Law of Superposition
G is younger than F. Which Principle is used?
Principle of Cross-Cutting Relationships

10. Principle of InclusionA B
Using the Principle of Inclusions, which picture shows the granite intrusion to be the youngest event? B

11. Conformable Beds
Beds that have not been disturbed

12. Uncomformities Substantial break or gap in the rock record 3 types
Angular
Disconformity
Nonconformity

13. Angular Unconformity
Older layers have been deformed, eroded, and younger layers deposited above

14. Disconformity
Beds are parallel relative to each other but there is a break in sequence
Implies a cessation of sedimentation or erosion, but no tilting
Hard to recognize

15. Nonconformity
Sedimentary layers overlie igneous or metamorphic layers

16. Unconformities Question: Answer: 1. Surface 1 is an example of ?
Nonconformity
2. Surface 2 is an example of ?
Angular unconformity
3. Surface 3, 4 and 5?
Disconformity
4. Granite is _________ than the Schist.
Younger

17. Correlating Rocks
Matching rocks of the same age in different locations

18. How do we correlate?
Walking out the contact
Matching fossils

19. Fossils
The remains or traces of prehistoric life

20. Types of Fossils Body fossils Trace fossils Bone, teeth, shells
Record movement

21. Fossilization
Hard parts
Unaltered

22. Fossilization - Petrified
Turned into stone
Petrified Forest, Arizona

23. Fossilization - Replacement
Minerals replace organic matter

24. Fossilization – Molds & Casts
Mold – impression or cavity
Cast – deposited material that fills cavity

25. Fossilization - Amber
Hardened Resin

26. Conditions favoring Preservation
Rapid burial
Possession of hard parts
Dies
Buried
Eroded

27. Fossils and Correlation
William Smith
Each rock formation contained fossils unlike the ones above & below
Sedimentary strata in widely separated areas could be identified & correlated by their fossil content

28. Principle of Fossil Succession
Fossils occur in a definite, invariable sequence in the geologic record
Apply with Law of Superposition and can document evolution of life through time

29. Index Fossils Widespread geographically
Limited to a short span of geologic time

30. Correlating Rocks & Fossils
Igneous rocks are dated radiometrically
Ages of fossils can be bracketed
Fossils in another area can be correlated containing same fossils
Age in another area determined indirectly
Doing this repeatedly the geologic time scale established

31. Geologic Time Scale