Ch.3, Sec.2 – Relative Dating: Which Came First? - determining whether an object or event is older or younger than other objects or events is called relative dating The Principle of Superposition - the idea that younger rocks lie above older rocks in undisturbed sequences is called superposition - unfortunately, not all rock layers are in this position, so aging them can be challenging!

Ch.3, Sec.2 – Relative Dating: Which Came First? The Geologic Column - geologists use the geologic column to help them age rocks, which may not be in the correct order because of rock disruptions like earthquakes & volcanoes

Ch.3, Sec.2 – Relative Dating: Which Came First? Disturbed Rock Layers - if rock layers are not horizontal, then the faults, folds, tilts, and intrusions must have come after the layers were created intrusion fault fold tilt

Ch.3, Sec.2 – Relative Dating: Which Came First? Gaps in the Record - Unconformities - missing rock layers create breaks in rock-layer sequences called unconformities - an unconformity is a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time

Ch.3, Sec.2 – Earth’s Story & Those Who First Listened