index fossils
TRANSCRIPT
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?