 Uniformitarianism- Principle that states that the same geological process shaping the Earth today have been at work throughout Earth’s history.  Examples: “The present is the key of the past” is a phrase that best summarizes uniformitarianism.

 Catastrophism- Principle that states that all geological change occurs suddenly.  Fact of Catastrophism: Supporters of catastrophism claimed that the formation of all Earth’s features, such as its mountains, canyons, and seas, could be explained by rare, sudden events called catastrophes.

 Relative dating- determining whether an object or event is older or younger than other objects or events  Superposition- principle that states that younger rocks lie above older rocks in undisturbed sequences.  Facts of superposition: “ Younger over older” is a phrase you can use to remember this principle.

 Geologic Column: Ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest.  Fact of geologic column: Geologists rely on the geologic column to interpret rock sequences.

 Unconformity- a surface that represents a missing part of the geologic column.  Steps to unconformity: 1. Deposition in this low area occurs as sediment is regularly supplied. 2. The sediment supply is cut off, and deposition stops. 2. Tectonic uplift exposes the area to erosion by water, wind, or other elements. 3. Sediment is supplied again, and deposition resumes. 3. Eventually, the area is worn down enough for deposition to start again.

 A fault and an intrusion are always younger than the layers they cut across.  Folding and tilting are events that are always younger than the rock layers they affect.

 Folding  Faulting

 Tilting  Intrusion

 These pictures all came from Google images.