IN: WHAT CAN YOU SAY ABOUT THE FOLLOWING PICTURE OF ROCK LAYERS?

6.2 Relative Dating: Which Came First?Pgs. 137-141

HOW DO GEOLOGISTS DETERMINE THE SEQUENCE OF EVENTS THAT FORMED THE ROCKS?

Relative Dating: Determining whether an object or event is older or younger than other objects or events.

THE PRINCIPLE OF SUPERPOSITION

A principle that states that younger rocks lie above older rocks in undisturbed sequences.

PRINCIPLE OF ORIGINAL HORIZONTALITY We assume that the sediments were

deposited horizontally. Any changes to that must have

happened afterwards.

DISTURBING FORCES

Sometimes the rocks are disturbed.

PRINCIPLE OF CROSS-CUTTING RELATIONSHIPS

The fault or intrusion must’ve come after the sediment was deposited.

THE GEOLOGIC COLUMN

The ideal sequence of rock layers that contains all theknown fossils and rock formations on Earth arrangedfrom oldest to youngest.

We use it to compare whenwe are not sure of the age of arock sequence.

MISSING EVIDENCE

Unconformities-when the surface is missing part of the geologic column.

THE GREAT UNCONFORMITY

OUT: What do you think happened to the series of rocks now?