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Table of Contents
Chapter Preview
8.1 The Rock Cycle
8.2 The Relative Age of Rocks
8.3 Radioactive Dating
8.4 Movement of Earth’s Plates
8.5 The Geological Time Scale
Chapter 8 Preview Questions
1. The laying down of sediment is
a. weathering.
b. erosion.
c. creep.
d. deposition.
Chapter 8 Preview Questions
1. The laying down of sediment is
a. weathering.
b. erosion.
c. creep.
d. deposition.
Chapter 8 Preview Questions
2. The movement of Earth’s landmasses is called
a. mass movement.
b. continental drift.
c. deposition.
d. Pangaea.
Chapter 8 Preview Questions
2. The movement of Earth’s landmasses is called
a. mass movement.
b. continental drift.
c. deposition.
d. Pangaea.
Chapter 8 Preview Questions
3. Evidence of Earth’s history can be found in
a. fossils.
b. climate change.
c. land features.
d. all of these.
Chapter 8 Preview Questions
3. Evidence of Earth’s history can be found in
a. fossils.
b. climate change.
c. land features.
d. all of these.
Chapter 8 Preview Questions
4. Which of the following is NOT a process in the rock cycle?
a. melting
b. weathering
c. continental drift
d. volcanic activity
Chapter 8 Preview Questions
4. Which of the following is NOT a process in the rock cycle?
a. melting
b. weathering
c. continental drift
d. volcanic activity
How does evidence from rocks help scientists
understand Earth’s history?
While hiking, you find a rock
containing a small fossil. The
fossil looks like the shell of a
present-day clam. When this
fossilized organism was alive,
what kind of environment
existed in the area where you
are hiking? Explain your answer.
Use Clues to Determine Meaning
A similar
example
The relative age of a rock is its age
compared to the ages of other rocks. You
have probably used the idea of relative
age when comparing your age with
someone elseís age, such as the age of
an older brother or younger sister. The
relative age of a rock does not give the
exact number in years since the rock was
formed.
What relative age
means?
What the term
does not mean
Apply It!
1. In your own words, explain what relative age means.
Relative age is someone or something’s age compared to the age of
someone or something else.
2. What familiar example is relative age compared to?
It is compared to the age of an older brother or younger sister.
Section 8.1:
The Rock Cycle
What is uniformitarianism?
What is the rock cycle?
THE THREE TYPES OF ROCKS
ROCKS = A MIXTURE OF MINERALS AND OTHER
MATERIALS.
IGNEOUS ROCKS FORM WITHIN THE EARTH AS
MOLTEN MAGMA.
SEDIMENTARY ROCK = FORM FROM THE WEATHERING
AWAY OF OTHER ROCKS.
METAMORPHIC ROCK = ROCKS THAT FORM FROM
SEDIMENTARY ROCK AFTER HEAT, PRESSURE OR
CHEMICALS CHANGE THEM.
IGNEOUS ROCKS
IGNEOUS ROCKS FORM WITHIN THE EARTH AS
MOLTEN MAGMA.
SEDIMENTARY ROCK
SEDIMENTARY ROCK = FORM FROM THE
WEATHERING AWAY OF OTHER ROCKS.
METAMORPHIC ROCK
METAMORPHIC ROCK = ROCKS THAT FORM FROM
SEDIMENTARY ROCK AFTER HEAT, PRESSURE OR
CHEMICALS CHANGE THEM.
A Cycle of Many Pathways
Forces deep inside Earth and at the surface produce a slow
cycle that builds, destroys, and changes the rocks in the
crust.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Rocks and the Rock Cycle
Rocks change continuously through the rock cycle.
Section 8.2:
The Relative
Age of Rocks
What is the law of superposition?
How do geologists determine the relative age of
rocks?
How are index fossils useful to geologists?
The Position of Rock Layers
GEOLOGISTS USE THE LAW OF SUPERPOSITION TO
HELP DETERMINE THE AGE OF ROCKS.
THE LAW STATES THAT ROCKS ON TOP OF OTHER
ROCKS ARE YOUNGER. AND THAT THE OLDEST ROCKS
ARE FOUND ON THE BOTTOM.
Determining Relative Age
To determine relative age, geologists also study extrusions
and intrusions of igneous rock, faults, and gaps in the
geologic record.
Determining Relative Age
An unconformity occurs where erosion wears away layers of
sedimentary rock. Other rock layers then form on top.
Determining Relative Age
An unconformity occurs where erosion wears away layers of
sedimentary rock. Other rock layers then form on top.
Determining Relative Age
An unconformity occurs where erosion wears away layers of
sedimentary rock. Other rock layers then form on top.
Determining Relative Age
An unconformity occurs where erosion wears away layers of
sedimentary rock. Other rock layers then form on top.
Using Fossils to Date Rocks
Index fossils are useful because they tell the relative ages of
the rock layers in which they occur.
FOSSILS
MOST FOSSILS ARE FOUND IN SEDIMENTARY ROCK.
FOSSILS PROVIDE EVIDENCE OF HOW LIFE HAS
CHANGED OVER TIME.
SCIENTISTS WHO STUDY FOSSILS ARE CALLED
PALEONTOLOGISTS.
THERE ARE VARIOUS KINDS OF FOSSILS DEPENDING
ON HOW THEY FORMED.
Section 8.3:
Radioactive Dating
What happens during radioactive decay?
What can be learned from radioactive dating?
What is the probably age of Earth?
Radioactive Decay
WHEN THE ATOMS IN ONE
ELEMENT ARE UNSTABLE
THEY LOSE PROTONS TO
BECOME ANOTHER
ELEMENT.
GEOLOGISTS USE
RADIOACTIVE DECAY TO
DETERMINE ABSOLUTE
AGES OF ROCKS.
THE RATE OF RADIOACTIVE
DECAY IS AN ELEMENTS
HALF-LIFE.
Radioactive Decay
POTASSIUM-ARGON DATING =
POTASSIUM-40 TURNS INTO
.
ARGON-40
IN RADIOACTIVE DECAY. THIS
DATING METHOD IS USED ON THE
MOST ANCIENT ROCKS.
CARBON –14 TURNS INTO
NITROGEN-14 AND IS VERY
USEFUL FOR DATING PLANTS AND
ANIMALS BECAUSE ALL PLANTS
AND ANIMALS HAVE CARBON 14 IN
THEM.
Radioactive Decay
The half-life of a radioactive element is the amount of time it
takes for half of the radioactive atoms to decay.
Determining Absolute Ages
Geologists use radioactive dating to determine the absolute
ages of rocks.
Percentages
What percentage of a radioactive element will be left after
three half-lives? First multiply 1/2 three times to determine
what fraction of the element will remain.
You can convert this fraction to a percentage by setting up a
proportion:
To find the value of d, begin by cross-multiplying, as for any
proportion:
1 x 100 = 8 x d
d=
d = 12.5%
Percentages
Practice Problem
What percent of a radioactive element will remain after five
half-lives?
3.125%
Section 8.4:
Movement of Earth’s
Plates
How does the theory of plate tectonics explain the
movement of Earth’s landmasses?
How has the movement of Earth’s plates affected
organisms?
Continental Drift
The theory of plate tectonics states that Earth’s landmasses have
changed position over time because they are part of plates that
are slowly moving.
Section 8.5:
The Geological
Time Scale
Why is the geological time scale used to show
Earth’s history?
What were early Precambrian organisms like?
What were the major events of the Paleozoic,
Mesozoic, and Cenozoic Eras?
The Precambrian Earth
The Precambrian Era
The earth forms from dust and gas 4.6 billion years ago
First Bacteria
First animals to use suns energy
The Paleozoic Era (ancient life)
Life explodes on the scene
Shelled animals form
Jawless fish evolve
Plants begin to grow on land
At the end, animals begin to invade land
Mass extinction (Pangaea)
The Mesozoic Era (middle ages)
The Mesozoic Era (middle ages)
Animals that survived the Paleozoic Era
Mammals began to appear
Dinosaurs began to dominate (Jurassic)
The first bird Archaeopteryx
Flowers evolved (Cretaceous)
Another mass extinction wiped out the dinosaurs
THE Cenozoic Era
The age of mammals
Marine mammals
Man evolves (quaternary)
The Geologic Time Scale
Because the
time span of
Earth’s past is
so great,
geologists use
the geologic
time scale to
show Earth’s
history.
Mass Extinctions
The graph shows how the
number of families of animals in
Earth’s oceans has changed.
Mass Extinctions
Reading Graphs:
What variable is shown on the
x-axis? On the y-axis of the
graph?
The x-axis shows time in
millions of years before the
present; the y-axis shows the
number of families of ocean
animals.
Mass Extinctions
Interpreting Data:
How long ago did the most
recent mass extinction occur?
Slightly more than 50 million
years ago
Mass Extinctions
Interpreting Data:
Which mass extinction
produced the greatest drop in
the number of families of
ocean animals?
The one that occurred about
230 million years ago
Mass Extinctions
Relating Cause and Effect:
In general, how did the
number of families change
between mass extinctions?
The number of families of
ocean animals immediately
dropped but then increased.
Geologic History
Geologic History
Geologic History
Geologic History