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Dating Rock Layers

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Dating Rock Layers How to tell how old the layers of rock are. What is Age? There are 2 kinds: Absolute Age The number of years since the rock formed. – PowerPoint PPT presentation

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Title: Dating Rock Layers


1
Dating Rock Layers
  • How to tell how old the layers of rock are.

2
What is Age?
  • There are 2 kinds
  • Absolute Age The number of years since the rock
    formed. (150 million years old, 10 thousand
    years old.)
  • Relative Age The age compared to the ages of
    other rocks. (older than this rock, younger than
    that rock.)

3
Age cont.
  • Relative Age Much easier to figure out. Can be
    deduced from clues on the Earth.
  • Absolute Age Much harder to figure out. Often
    impossible.

4
What are the ways to tell RELATIVE AGE.
  • 1. Law of Superposition
  • 2. Extrusion Intrusion
  • 3. Faults
  • 4. Unconformities

5
What is the Law of Superposition?
  • In horizontal sedimentary rock layers, the
    oldest layer is at the bottom. Each higher layer
    is younger than the layers below it.

6
Age and Superposition
7
What is Extrusion?
  • When magma cools on the surface of the Earth its
    called an EXTRUSION.
  • Extrusions are always YOUNGER than the rock it is
    sitting on.
  • For extrusion think exit or outside.

8
What is an Intrusion?
  • When magma cools beneath the surface of the Earth
    its called an INTRUSION.
  • Intrusions are always YOUNGER than the rocks
    around it.
  • For intrusion think inside.

9
Heres an Intrusion
10
Extrusions? Intrusions?
First of all, which rock layer is the oldest?
What is this called?
EXTRUSION
INTRUSION
11
What is a Fault?
  • A BREAK in the Earths crust.
  • A fault is always YOUNGER than the rock it cuts
    through.
  • Faults move over time, making determining the age
    of the layers confusing.

12
Heres a Fault
13
Faults
Faults move over time causing the rock layers to
move.
14
Faults
As more time goes by, more rock layers are added
on top. Making aging the rock layers difficult.
15
Faults
Geologists must then label each of the rock
layers. This can be tough because they werent
around to see the whole process occur.
16
What is an Unconformity?
  • The surface where new rock layers meet a much
    older rock surface beneath them.
  • An unconformity shows where some rock layers have
    been lost because of erosion.

17
Unconformity
18
Summary
  • Relative vs. Absolute Age
  • Determining Relative Age
  • Law of Superposition on top is younger
  • Intrusions magma inside Earth.
  • Extrusions magma on top of Earth.
  • Faults breaks in the crust
  • Unconformities signs of erosion.
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