1. Principle of Superposition
Determining the Relative Age of a Geologic Area

2. Principle of Superposition
In a stack of undisturbed sedimentary rock layers, the layers on the bottom were deposited before the layers on top.
Relative age tells how old something is when compared to something else.

3. Superposition and the Fossil Record
Layers of rocks are called strata.
Four principles help geologists study strata and interpret the rocks’ history.
Superposition
Cross-cutting relationships
Original horizontality
Original lateral continuity

4. Principle of Cross-cutting
Surface
Impact Crater
Two Basic Rules of Relative Age Dating
Cross-Cutting Relationships
Principle of Superposition
The surface of Mars has been hit with an impact crater. The impact crater and surface of Mars has been cut by another feature called a fracture. The fracture is the CROSS-Cutting feature. Using Relative Age Dating techniques, the surface is the oldest, the impact crater the next oldest, and the channel is the youngest. This is called Relative Age Dating by Cross-cutting relationships.
Principle of Cross-cutting

5. Principle of Superposition
Two Basic Rules of Relative Age Dating
Cross-Cutting Relationships
Principle of Superposition
This demonstrates the Principle of Superposition. Crater #1 is partly covered crater #2, so crater #1 is older.
Crater #2 is partly covered by crater #3, which makes crater #2 older than crater # 2 older than crater #3.
By the Principle of Superposition, crater #1 is the youngest feature, This is known as the principle of Superposition.
Principle of Superposition

6. Principle of Superposition
Relative Age Dating
Oldest Feature?
Younger Feature?
Youngest Feature?
A = Oldest
C = Youngest
B = 2nd Oldest
Based on the two relative age dating principles (cross-cutting relationships and superposition) let’s interpret the relative ages of the features in this image. We’ll make the inference that the surface is the oldest feature, so we are Relative Age Dating the features A,B, & C
Principle of Superposition

7. Original horizontality
Remaining Principles
Original horizontality

8. Sedimentary rocks form layers that cover large areas.
Original lateral continuity:
Sedimentary rocks form layers that cover large areas.

9. Fossils and Relative Age
Geologists keep track of which fossils came from which strata and apply the principle of superposition.
Fossil occurrences in layers are used to confirm or assign relative ages to rock strata.

10. C original lateral continuity D uniformitarianism
What principle states that processes at work today are the same processes that occurred in Earth’s past?
A superposition
B relative age
C original lateral continuity
D uniformitarianism
Lesson 1 Review

11. What type of rock is formed when put under extreme pressure or heat?
A igneous
B metamorphic
C strata
D sedimentary
Lesson 1 Review

12. What process slows or stops sediments in low areas of the landscape?
A deposition
B lithification
C weathering
D transportation
Lesson 1 Review

13. Steno’s Principle page 290
Select one of Nicolas Steno’s four principles of Relative Age Dating
Create a drawing that represents that principle.
Label your drawing
Write a summary explaining your diagram
Due Friday
Steno’s Principle page 290

14. End of Lesson 1