Principles of Relative Dating

Front

the age of rocks and geologic features compared with other rocks and features nearby

Back

relative age

Front

the exact age of something

Back

absolute age

Front

in undisturbed rock layers, each layer of rocks is younger than the layer below it

Back

superposition

Front

rock layers are deposited horizontally because of gravity; if layers are not horizontal, it is because of an event that occurred afterwards

Back

original horizontality

Front

a feature like a fault line or igneous rock intrusion that cuts across a horizontal layer is younger than the layer that it cuts through

Back

cross-cutting relationships

Front

rock layers that contain pieces of other rocks must be younger than the rocks they include

Back

inclusions

Front

rock layers form in continuous sheets (so a layer exposed on one side of a canyon likely spanned the canyon at one time)

Back

lateral continuity