DO NOW (Period 2 & 7 only)

Use answer key to make correction to p. 2 in binder

DO NOW QUESTION

What kind of unconformity is shown below? Explain.

Choices:• Disconformity • Nonconformity• Angular Nonconformity

RELATIVE DATING: WHICH CAME FIRST?

Chapter 6.2

WHAT IS RELATIVE DATING?

Used to determine which events happened in Earth’s past

Used to determine if an object/event is older or younger than other objects/events

WHAT IS RELATIVE DATING?

PUT IN ORDER FROM OLDEST TO YOUNGEST…

A B C D

OLDEST C A B D YOUNGEST

WHAT IS THE PRINCIPLE OF SUPERPOSITION? Younger rocks lie above older

rocks in undisturbed sequences

Sequence = order

IN WHAT ORDER (SEQUENCE) WAS THIS CAKE WAS CREATED?

1. Purple (oldest – laid down first)

2. Blue3. Green4. Yellow5. Orange6. Red (youngest – laid down last)

Grand Canyon – Arizona, USA

HOW DO GEOLOGISTS USE THE GEOLOGIC COLUMN? Undisturbed sequence of rock layers

containing fossils and rock formations

Arranged from oldest to youngest

Geologists use to interpret information in rock sequences

Created by combining data from all known rock sequences in an area

HOW CAN A ROCK LAYER CAN BE DISTURBED? Fault break in Earth’s crust where plates slide past one another

Intrusion molten rock inside Earth pushes into rock and cools

Foldingrock layers bend and buckle from forces in Earth

Tiltingforces in Earth slant rock layers

FAULT break in Earth’s crust where plates

slide past one another

INTRUSION• molten rock inside Earth pushes into rock and

cools

FOLDING• rock layers bend and buckle from forces in Earth

TILTING• forces in Earth slant rock layers

WHAT IS AN UNCONFORMITY? Surface that represents a missing

part of the geologic column (missing rock layer)

Caused by nondeposition (sediment is no longer being despoited) or erosion (transport of sediment elsewhere)

HOW DOES A DISCONFORMITY OCCUR?1. Rock layers are uplifted and

eroded away2. In the future, sediment is

deposited on top of the old erosion surface

Most common type of unconformity Part of a horizontal sedimentary

rock sequence is missing

HOW DOES A NONCONFORMITY OCCUR?1. Intrusive igneous or metamorphic

rock is uplifted and eroded away2. In the future, sediment is

deposited on top of this igneous or metamorphic rock

Horizontal sedimentary rock layers on top of eroded surface of older igneous or metamorphic rock

HOW DOES A ANGULAR NONCONFORMITY OCCUR?1. Forces in Earth tilt of fold layers of

rock2. Tilted or folded rock is uplifted and

eroded away3. In the future, horizontal layers of

sediment is deposited

Occurs between horizontal layers of sedimentary rock and tilted or folded layers of sedimentary rock