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

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 Sedimentary Rocks Igneous Rocks 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