November 2,2011

Objective: To learn how

geologists infer the logical sequence of events and establish a probable relative age for a series of rock layers

Agenda:Law of

superposition notesText book questions

Page 204-205 answer questions 4,12,13

Geologic Timeline hanging

Lab: Law of Superposition

Discovering Earth’s HistoryPrinciple of

Uniformitarianism:The forces and

processes happening today have been going on for a long time

Key PrinciplesRelative Dating

Tells us the sequence in which events occurred

Law of SuperpositionIn sedimentary

rocks, each bed is older than the one above it and younger than the one below it

Law of Superposition

Younger Layers→

Older Layers→

Ordering the Grand Canyon’s History

Disturbed Rock Layers

Relative Dating—Key Principles

Principle of Cross-Cutting Relationships• The principle of cross-cutting relationships

states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.

Applying Cross-Cutting Relationships

Formation of Inclusions

Relative Dating—Key Principles

Unconformities• An unconformity represents a long period

during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed.

Formation of an Angular Conformity

Relative Dating—Key Principles

Unconformities• A break in the geologic record created when rock

layers are eroded or when sediment is not deposited for a long period of time.

A Record of Uplift, Erosion, and Deposition

Correlation of Rock Layers or walking the outcrop

Correlation is establishing the equivalence of rocks of similar age in different areas.

Correlation of Strata at Three Locations