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• James Hutton proposed the principle of uniformitarianism.
• This states that the processes occurring on Earth today, have been occurring since Earth first formed.
• In other words, “the present is the key to the past”.
• Relative dating of rocks is getting an approximate age of the rock formation, without being able to get an EXACT age.
• In this picture of the Grand Canyon, each horizontal layer of rocks represents a different chunk of time.
Relative Geologic Dating
It states that sedimentary rocks are always deposited in horizontal layers, unless something has happened to fold or fault them.Think of a layer cake!!!!! Layers
The first geological principle is the Principle of Original Horizontality
Principle of Superposition
The second principle goes along with the first. Because sedimentary rocks are deposited horizontally, the one on the bottom must be the oldest and each
layer on top of that gets younger, with the youngest on the top.
This is called the Principle of Superpostion
Superposition*oldest layers are on the
bottom
Original Horizontality*rocks form horizontal
layers
youngest
oldest
The third principle is the Principle of Cross-Cutting Relationships
This states that an igneous rock intrusion or a fault must be younger than the rock it cuts across.
In other words, the pizza or cake has to be baked before you can cut it!!
Cross - cutting features are younger
canyons intrusions faults
• Earth’s surfaces are constantly being eroded.
• Because of this, often there is a gap in the rock record.
• These gaps are called unconformities.
• There are 3 types of unconformities.
1. Angular Unconformity
Rock layers above and below the un-conformity are at an angle to each other
horizontal layers
tilted layers
2. Disconformity
Rock layers above and below the un-conformity are parallel to each other
horizontal layers
horizontal layers
3. Nonconformity
Rock layers above and below the un-conformity are different rock types
sedimentary
igneous or metamorphic
Nonconformity – sedimentary rocks deposited on igneous or metamorphic rocks that have been subject to erosion
SedimentaryRocks
IgneousRocks
Nonconformity
1. A
2. C
3. D
4. E
5. F
6. B
Oldest
Youngest
This symbol tells you that intrusion A changed all the rocks it touched. Meaning it must be younger than any rock it changed
What type of rock would be found where the is?
Give the actual NAME of a rock one might find at that point.
Metamorphic Rock
Using page 7 of your ESRT’s Limestone turns into Marble