1. Investigation 4: My Sediments Exactly Earth History Grade 6
Earth’s Layers
Investigation 4: My Sediments Exactly
Earth History
Grade 6

2. Layers
Geologists observed that, usually, when sediments settle in a basin, they form a flat, horizontal layer.
Horizontal: level (like a floor), not higher on one side or the other.

3. Principle of Original Horizontality
Each new deposit of sediment forms a new horizontal layer on top of the layers below.
Principle of Original Horizontality: layers of sediment are generally deposited in a horizontal or nearly horizontal position.

4. Uniformitarianism
Uniformitarianism: the present is the key to the past.
Geologists use the observations they make about processes happening today, such as erosion, deposition, and the formation of sand and clay to infer events that happened in the past, events that they weren’t able to observe.

5. Uniform
The way things happen today is the same way things have always happened. The processes are uniform.