• 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