The Relative Age of Rocks
The relative age of a rock is its _______________ compared to the ages of other rocks.
 Ex. Mrs. Herrscher is older than her sister and brother.
The absolute age of a rock is the _________________ of years that have passed since the rock formed.
 Ex. Mrs. Herrscher is 33 years old.
It may be impossible to know a rock’s absolute age exactly, so geologists often use both
__________________ and __________________ ages.
How old are rock layers?
According to the ____________of ____________________________, in undisturbed horizontal
sedimentary rock layers, the oldest layer is at the __________________.
Each higher layer is ______________________ than the layers below it.
The _________________________ of original horizontality states that most sedimentary layers of rock are deposited in a _______________________ position.
Clues from Igneous Rock
Lava that hardens on the surface and forms igneous rock is called an
______________________.
 An extrusion is always _____________________ than the rocks below it.
When magma cools and hardens into a mass of igneous rock beneath the surface, it is called an
___________________.
 An intrusion is always younger than the rock layers around and beneath it.
Clues from Fossils
A _________________ is a break in the Earth’s crust.


A fault is always younger than the rock it cuts through.
??? Why do you think a fault is always younger than the rock it cuts through?
Answer: ____________________________________________________________________
 An ____________________ fossil is a fossil that is ______________________ distributed and represents an organism that only existed for a ___________________ period of time.

Index fossils are useful because they tell the ___________________________________ ages of the rock layers in which they occur.
Clues with Fossils
How can rock layers change?
 ____________________ in the geologic record and _________________ can change the position in which rock layers appear.

An _______________________________ is a gap in the geologic record. It shows where rock layers have been lost due to __________________________.