Relative Age & Folding
What is relative age?
The age of a rock compared to the ages of other rocks.
What is absolute age?
The age of a rock given as the number of years since the earth formed.
What is the law of superposition?
The geologic principle that states in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.
What is a fault?
A break in Earth's crust along which rocks move.
What is an index fossil?
Fossils of widely distributed organisms that lived during a geologically short period.
The relative age of a rock is the number of ____ that passed since the rock formed.
Years
What happens when rock layers erode?
An older rock layer may be exposed.
How Old are Rock Layers? (KC 1)
According to the law of superposition, in undisturbed horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
What are the types of igneous rocks?
Extrusion, intrusion, magma/lava
What is an uncomformity?
A gap in the geologic record that shows where rock layers have been lost due to erosion.
What happens when forces inside Earth fold?
They fold rock layers so much that the layers are turned over completely.
What do geologists use to determine the relative ages of sedimentary rocks?
What is missing?
Extrusion: An igneous rock layer formed when _____ flows onto Earth's surface and hardens
Intrusion: An igneous rock layer formed when _____ hardens beneath Earth's surface
Lava, magma
How Old Are Rock Layers? (KC 2)
Index fossils are useful because they tell the relative ages of rock layers in which they occur.
What causes the movement of rocks on the opposite sides of a fault?
Forces inside Earth
How can Rock Layers change?
Gaps in the geologic record and folding can change the position in which rock layers.
How do geologists find the relative age of the youngest layer?
Faults
How is an index fossil useful?
To be useful as an index fossil, a fossil must be widely distributed and represent an organism that existed for a geologically short period of time.