Relative Age

Age of a rock compared to the ages of other rocks

Absolute Age

Number of years since

the rock formed

Law of Superpositi

on• Scientists use to

determine RELATIVE age of a rock

• Youngest layer is always located on the top, oldest layer always located on the bottom

Law of Superposition Activity

•Rock layers T and C are the oldest

•Each card must contain one common letter

•Place cards in order as they might appear in a canyon

•How do you know X is older than M?

•Explain why D in the rock layer represented by DM is the same age as M

•Explain why D in the rock layer OXD is older than D in the rock layer DM

Index Fossils

Fossils of widely distributed

organisms that lived during only one short time

period

Index Fossil?

Index Fossil?

How has the environment

changed?

Determining Relative Age using fossil

evidence• Sequence the cards

according to relative age

• Keep in mind that extinction is forever

• Layer M is the oldest

How’d you do?

• What clues did you use to help you determine the rock sequence?

• Are any of the fossils good index fossils? Why?

Reflection page 42Reflection page 42

If humans were to suddenly become extinct, do you think

that we would be a good index fossil? Why or why not?