Relative Dating Notes

Relative Age of Rocks Relative Dating: Order rocks deposited tells you relative age of rocks (order from old to young) Geologic Cross-Section Maps: show the structure of rocks underground. Can determine the relative age of rocks by using 5 geologic principles:

Law of Superposition: In sedimentary rock, the oldest layer is on bottom & youngest is on top.

Canyonlands, Utah

Law of Original Horizontality: Sediments deposited in flat, horizontal layers. If rock layers are folded or at an angle, they were disturbed after originally deposited

Raplee Monocline, Utah

Unconformity: Surface where a break in deposition of sediments occurred or period of erosion.

Eastern Grand Canyon

Law of Cross Cutting Relationships: Fault lines or igneous rock intrusions are younger than the rock it cuts across.

Hance Rapids, Grand Canyon

Principle of Inclusion: Rock material trapped inside igneous intrusion or sedimentary rock layer is older than rock that surrounds it.

Lake Pleasant