1. Principle of Uniformitarianism
The same laws
and processes operating on
Earth throughout geologic time
are the same laws
and processes operating today
Weather/Climate
Mountain building
Volcanism
Earthquakes
Erosion
Deposition

2. Law of Superposition
Younger layers of rock are deposited on top of older layers of rock. (Relative Dating)

3. What is the relative age of the lava and the road?
Why can’t an absolute age be determined?

4. Stratigraphic Sequence
Zion Canyon, UT
Younger Rock Layers
Stratigraphic Sequence
Older Rock Layers

5. Intrusion
An exception to the
Law of Superposition!

6. Formation of Sedimentary Rocks

7. A B C D
Which layer is
a) Oldest?
b) Youngest?

8. Law of Original Horizontality
Sedimentary rocks are originally deposited in horizontal layers

9. Later, they can be bent or tilted due to collisions between tectonic plates.

10. Law of Lateral Continuity
erosion may remove some areas of rock layers, but they can be assumed to belong to a larger original sequence.

11. Original Horizontality
Grand Canyon, AZ
Original Horizontality
Lateral Continuity

13. How did these Southern Alberta Hoodoos form?

14. Unconformity: layers may be missing due to erosion, the boundary left behind where such a gap is missing is called an unconformity.

15. Rank the rock layers from oldest to youngest.
Identify the unconformity.

16. Uncomformities – Intrusive Igneous Rock
Volcanic rocks that melt and cut their way through rocks, must be younger than the layers they cut through.

17. The Devils Tower in Wyoming is an example of a volcanic neck
The Devils Tower in Wyoming is an example of a volcanic neck. Magma was intruded into the neck of a volcano and cooled to form an intrusive igneous rock. As the magma cooled it contracted and cracked into the vertical columns shown in the picture. This feature, called columnar jointing, is described further on in this module. After intrusion of the volcanic neck, the volcano became extinct and eventually, after a long period of time, eroded completely away, leaving only the hard, resistant rock in the volcanic neck to stand up above the surrounding countryside.

18. Rank the rock layers from oldest to youngest.
Identify the unconformity.

19. versus Law of Superposition
RELATIVE DATING: Determining which rock layers and fossils are older and which are younger (i.e. determining which era/period/epoch a fossil or layer belongs to).
Law of Superposition
Low of Original Horizontality
Law of Lateral Continuity
Law of Cross-Cutting Relationships
versus
Radiometric Dating
ABSOLUTE DATING: Determining age (in years) of a rock layer or fossil

20. Determining which fossil species appeared in what order in time.
Relative Dating Techniques
- Fossil Succession
Determining which fossil species appeared in what order in time.

21. Index fossils should be: common easily recognizable
Relative Dating Techniques - Correlation
Index Fossils: fossils that can help determine the relative ages of rocks and correlate rock sequences from different locations.
Index fossils should be:
common
easily recognizable
occurred over a large area
relatively short time

22. William Smith
( )

24. The Grand Record

25. Forces of Catastrophe