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Bellringers
Chapter Presentation
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Chapter 21
Planet Earth
Table of Contents
Section 1 Earth’s Interior and Plate Tectonics
Section 2 Earthquakes and Volcanoes
Section 3 Minerals and Rocks
Section 4 Weathering and Erosion
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Objectives
• Identify Earth’s different geologic layers.
• Explain how the presence of magnetic bands on the
ocean floor supports the theory of plate tectonics.
• Describe the movement of Earth’s lithosphere using the
theory of plate tectonics.
• Identify the three types of plate boundaries and the
principal structures that form at each of these boundaries.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Bellringer
A peach can be used as a model for some aspects of Earth’s
structure. Compare the drawing of the cross section of the
peach below with the cross section of Earth to its right, and
answer the following questions.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Bellringer, continued
1. Describe the outer layer of the peach (the skin). What
aspect of Earth’s structure does the outer layer of the
peach represent?
2. The peach pulp is the next layer. How would you
describe it? What aspect of Earth’s structure does the
peach pulp represent?
3. The pit is the innermost part of the peach. What is the
pit like? What aspect of Earth’s structure does the
peach pit represent?
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
What is Earth’s Interior Like?
• The Earth is made up of three layes: the crust, the
mantle and the core.
• Crust the thin and solid outermost layer of Earth
above the mantle
• Mantle the layer of rock between Earth’s crust and
core
• Core the center part of the Earth below the mantle
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Structure of the Earth
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Formation of Earth’s Crust, Mantle, and Core
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
What is Earth’s Interior Like? continued
• Earth’s interior gets warmer with depth.
• Geologists believe that the mantle is much hotter
than the crust, reaching temperatures higher than
1250° C (2280° F).
• The core is hotter than the mantle, reaching
temperatures higher than 6000° C (10,800° F).
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Magma
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Magma and Vents
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
What is Earth’s Interior Like? continued
• Radioactive elements contribute to Earth’s high
internal temperature.
• The breakdown of radioactive isotopes uranium,
thorium and potassium give off energy that
contributes to Earth’s high internal temperatures.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics
• Around 1915, German scientist Alfred Wegener
proposed the idea that the continents were once
united as a supercontinent and then drifted apart.
• He pieced the continents together like a puzzle
and called the supercontinent they formed
Pangaea.
• Wegener found identical fossils on widely
separate continents, which supported his idea.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Continental Drift (Pangaea)
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics, continued
• Evidence for Wegener’s ideas came later.
• Wegener’s theory of continental drift was ignored
until structures discovered on the ocean floor
provided evidence for a mechanism for the
movement of continents.
• Symmetrical bands on either side of a mid-ocean
ridge indicate that the two sides of the ridge were
moving away from each other and new ocean
floor was rising up between them.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics, continued
• Alignment of oceanic rocks supports the theory of
moving plates.
• Iron in molten rock aligns itself with Earth’s
magnetic field as it cools.
• The Earth’s magnetic field reverses polarity about
every 200,000 years
• The process is recorded as magnetic bands in
rock, based on the age of the rock.
• Symmetrical bands on either side of the Mid
Atlantic Ridge suggest that the crust was moving
away from the ridge.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics, continued
• Earth has plates that move over the mantle.
• The crust and upper portion of the mantle are
divided into about seven large pieces called
tectonic plates.
• Lithosphere the solid, outer layer of Earth, that
consists of the crust and the rigid upper mantle
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics, continued
• Plate tectonics the theory that explains how the
outer parts of Earth change through time, and that
explains the relationships between continental drift,
sea-floor spreading, seismic activity, and volcanic
activity
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Tectonic Plates
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Tectonics, continued
• It is unknown exactly why tectonic plates move.
• One hypothesis suggests that plate movement
results from convection currents in the
asthenosphere, the hot, fluid portion of the mantle.
• Another hypothesis suggests that plate movement
results from the force of gravity acting on the
plates.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Boundaries
• Mid-ocean ridges result from divergent boundaries.
• The border between two plates is called a
boundary.
• Divergent boundary a place where two plates are
moving apart
• New rock forms between divergent boundaries.
• Magma liquid rock produced under Earth’s surface
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Divergent and Convergent Boundaries
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Convergent Boundary
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Boundaries, continued
• Oceanic plates dive beneath continental plates at
convergent boundaries.
• Plates slide over each other at a convergent
boundary.
• Subduction the process by which one lithospheric
plate moves beneath another as a result of tectonic
forces
• The area where one plate slides over another is
called a subduction zone. Subduction zones produce
ocean trenches, mountains, and volcanoes.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Subduction Zone
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Boundaries, continued
• Subduction of ocean crust generates volcanoes.
• Chains of volcanoes form on the upper plate in a
subduction zone.
• These volcanoes can form far inland from their
associated oceanic trench.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Boundaries, continued
• Colliding tectonic plates create mountains.
• When two plates collide, mountains are formed at
the boundary of the collision.
• The Himalayas formed during the collision
between the continental tectonic plate containing
India and the Eurasian continental plate.
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Chapter 21
Section 1 Earth’s Interior and
Plate Tectonics
Plate Boundaries, continued
• Transform fault boundaries can crack Earth.
• Plate movement can cause breaks in the
lithosphere.
• Fault a crack in Earth created when rocks on either
side of a break move
• Plate movement at transform fault boundaries is
one cause of earthquakes.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Objectives
• Identify the causes of earthquakes.
• Distinguish between primary, secondary, and
surface waves in earthquakes.
• Describe how earthquakes are measured and rated.
• Explain how and where volcanoes occur.
• Describe the different types of common volcanoes.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Bellringer
1. Imagine a corked bottle of soda pop that is standing
in a pan of hot water. What do you think will happen as
the soda pop heats up?
2. What happens when the pressure builds up in the
soda pop?
3. Molten rock in Earth’s mantle is like the soda pop.
What happens when pressure builds up in Earth’s
mantle?
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Chapter 21
Section 2 Earthquakes and
Volcanoes
What are Earthquakes?
• Earthquakes occur at plate boundaries.
• Earthquakes are vibrations resulting from rocks
sliding past each other at a fault
• Seismic waves are waves of energy released
during in earthquake
• Focus the area along a fault at which the first
motion of an earthquake occurs
• Epicenter the point on Earth’s surface directly
above an earthquake’s focus
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Chapter 21
Section 2 Earthquakes and
Volcanoes
What are Earthquakes? continued
• Energy from earthquakes is transferred by waves.
• Earthquakes generate three types of waves:
• Longitudinal waves
• Transverse waves
• Surface waves
• Longitudinal waves travel by compressing and
stretching crust, also called primary waves (P waves)
• Transverse waves travel in an up and downward
movement, also called secondary waves (S waves)
• Surface waves seismic waves that can move only
through solids, move in a rolling circular motion
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Longitudinal Waves
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Transverse Wave
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Seismic Waves: Surface Waves
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Chapter 21
Section 2 Earthquakes and
Volcanoes
What are Earthquakes? continued
• Waves move through Earth and along its surface.
• Both P waves and S waves spread out from the
focus in all directions through the earth.
• Surface waves move only on Earth’s surface.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Measuring Earthquakes
• Seismologists detect and measure earthquakes.
• Seismology the study of earthquakes including their
origin, propagation, energy, and prediction
• Seismologists use sensitive equipment called
seismographs to record data about earthquakes.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Seismographs and Mapping Earth’s Layers
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Measuring Earthquakes, continued
• Three seismograph stations are necessary to locate
the epicenter of an earthquake.
• There are more than 1000 seismograph stations
across the world.
• Because P waves travel faster, the difference
between the arrival of P waves and the arrival of S
waves allows scientists to calculate how far away
the focus is.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Measuring Earthquakes, continued
• Geologists use seismographs to investigate Earth’s
interior.
• The way P and S waves travel through Earth’s
interior help scientists make a model of Earth with
layers of different densities.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Measuring Earthquakes, continued
• The Richter scale is a measure of the magnitude of
earthquakes.
• Richter scale a scale that expresses the magnitude
of an earthquake
• The intensity of an earthquake is measured by the
modified Mercalli scale. Intensity depends on many
factors.
• Earthquakes that occur deeper below the Earth’s surface
will not be as intense at the surface.
• The hardness of the rock above and around an
earthquake affects the intensity.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Richter Scale
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Measuring Earthquakes, continued
• Scientists are trying to predict earthquakes.
• Scientists are trying to measure changes in
Earth’s crust that might signal an earthquake.
• The ability to predict an earthquake could save
thousands of lives in the future.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes
• A volcano is any opening in Earth’s crust through
which magma has reached Earth’s surface.
• Vent an opening at the surface of Earth through
which volcanic material passes
• Volcanoes generally have one central vent, but
they can also have several smaller vents.
• Magma that reaches Earth’s surface is called lava.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Shield volcanoes have mild eruptions.
• Lava from shield volcanoes is very fluid and forms
a gently sloping mountain.
• Shield volcanoes are some of the largest
volcanoes.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Composite volcanoes have trapped gas.
• Composite volcanoes are made up of alternating
layers of ash, cinders, and lava.
• The lave is thicker than that of shield volcanoes.
• Gases are trapped in the magma, causing
eruptions that alternate between flows and
explosive activity that produces cinders and ash.
• Composite volcanoes are typically tall with steep
sides.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Cinder cones are the most abundant volcano.
• Cinder cones are the smallest and most common
volcanoes.
• Large amounts of gas are trapped in the magma,
and violent eruptions of hot ash and lava occur.
• Cinder cones tend to be active for only a short
time and then become dormant.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Types of Volcanoes
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Most volcanoes occur at convergent plate
boundaries.
• 75% of the active volcanoes on Earth are located
in an area known as the Ring of Fire.
• The Ring of Fire is located along the edges of the
Pacific ocean, where oceanic tectonic plates are
colliding with continental plates.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Ring of Fire
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Underwater volcanoes occur at divergent plate
boundaries.
• As plates move apart at divergent boundaries,
magma rises to fill the gap.
• This magma creates the volcanic mountains that
form ocean ridges.
• Iceland is a volcanic island on the Mid-Atlantic
ridge that is growing outward in opposite
directions.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Volcanoes, continued
• Volcanoes occur at hot spots.
• Some volcanoes occur in the middle of plates.
• Mantle plumes are mushroom shaped trails of hot rock
that rise from deep inside the mantle, melt as they rise,
and erupt from volcanoes at hot spots at the surface.
• The plumes remain in the same place as the tectonic
plate moves, creating a trail of volcanoes.
• The Hawaiian Islands are an example of this type of
volcanic activity.
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Chapter 21
Section 2 Earthquakes and
Volcanoes
Hot Spots and Mantle Plumes
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Chapter 21
Section 3 Minerals and Rocks
Objectives
• Identify the three types of rock.
• Explain the properties of each type of rock based on
physical and chemical conditions under which the
rock formed.
• Describe the rock cycle and how rocks change form.
• Explain how the relative and absolute ages of rocks
are determined.
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Chapter 21
Section 3 Minerals and Rocks
Bellringer
In this section you will be studying rocks and minerals. Rocks are identified
by the minerals they contain, the size of their crystals, and other
properties. Using the following flowchart, list the properties of the rocks
named below.
1.
2.
3.
4.
5.
Rock is light colored. go to 2
Rock is dark colored. go to 4
Rock has large crystals. Granite
Rock has small crystals. go to 3
Rock is very light and fine grained with a streak of color. Marble
Rock is fine grained with definite layers. sandstone
Rock has definite small crystals. Basalt
Rock has no obvious crystal structure. go to 5
Rock is hard, dark, and glasslike. Obsidian
Rock is porous, has air bubbles, and crumbles when rubbed over
a hard surface. pumice
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Chapter 21
Section 3 Minerals and Rocks
Bellringer, continued
Using the flowchart on the previous slide, list the
properties of the rocks named below.
Granite
Basalt
Obsidian
Sandstone
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks
• All rocks are composed of minerals.
• There are about 3500 known minerals in Earth’s
crust.
• Each combination of rock-forming minerals results
in a rock with a unique set of properties.
• Mineral a natural, usually inorganic solid that has a
characteristic chemical composition, an orderly
internal structure, and a characteristic set of physical
properties
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
• Molten rock cools to form igneous rock.
• Nearly all igneous rocks are made of crystals of
various minerals.
• Igneous rock rock that forms with magma cools and
solidifies
• Extrusive igneous rock cools on Earths surface
• Intrusive igneous rock cools while trapped beneath
Earth’s surface
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Chapter 21
Section 3 Minerals and Rocks
Comparing Intrusive and Extrusive Igneous
Rock
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
• Remains of older rocks and organisms form
sedimentary rocks.
• All rock breaks down over thousands of years.
• Weathering the natural process by which
atmospheric and environmental agents, such as
wind, rain, and temperature changes, disintegrate
and decompose rocks
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Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
• As pieces of rock accumulate, they can form another
type of rock.
• Sedimentary rock a rock formed from compressed
or cemented layers of sediment
• Sediment accumulated pieces of rock and other
particles
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
•
Loose sediment forms rock in two ways.
1. Layers of sediment get compressed from weight
above, forming rock.
2. Minerals dissolved in water seep between bits of
sediment and “glue” them together.
•
Sedimentary rocks are named according to the size
of the fragments they contain.
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
• Rocks that undergo pressure and heating without
melting form metamorphic rock.
• Heat and pressure within Earth cause changes in
the texture and mineral content of rocks.
• Metamorphic rock a rock that forms from other
rocks as a result of intense heat, pressure, or
chemical processes
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Chapter 21
Section 3 Minerals and Rocks
Types of Rock
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Chapter 21
Section 3 Minerals and Rocks
Structure and Origin of Rocks, continued
• Old rocks in the rock cycle form new rocks.
• The sequence of events in which rocks can be
weathered, melted, altered, and formed is
described by the rock cycle.
• Rock formation occurs very slowly, often over tens
of thousands to millions of years.
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Chapter 21
Section 3 Minerals and Rocks
The Rock Cycle
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Chapter 21
Section 3 Minerals and Rocks
How Old Are Rocks?
• The relative age of rocks can be determined using
the principle of superposition.
• The principle of superposition states the following:
• Assuming no disturbance in the position of the rock
layers, the oldes will be on the bottom, and the
youngest will be on top.
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Chapter 21
Section 3 Minerals and Rocks
Law of Superposition
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Chapter 21
Section 3 Minerals and Rocks
How Old Are Rocks? continued
• Radioactive dating can determine a more exact, or
absolute, age of rocks.
• The radioactive elements that make up minerals in
rocks decay over billions of years.
• Physicists have determined the rate at which
these elements decay.
• Geologists can use this data to determine the age
of rocks.
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Chapter 21
Section 4 Weathering and
Erosion
Objectives
• Distinguish between chemical and physical
weathering.
• Explain how chemical weathering can form
underground caves in limestone.
• Describe the importance of water to chemical
weathering.
• Identify three different physical elements that can
cause erosion.
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Chapter 21
Section 4 Weathering and
Erosion
Bellringer
1. What features of a wave allow it to move sand as the
wave rolls onto a beach?
2. The Colorado River flows through the Grand Canyon.
What do you think made the Grand Canyon?
3. What are some other environmental factors that
change the land?
4. How do you think potholes form in a road?
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Chapter 21
Section 4 Weathering and
Erosion
Physical Weathering
• There are two types of weathering: physical and
chemical.
• Physical (or mechanical) weathering breaks rocks
into smaller pieces, but does not alter their
chemical compositions.
• Chemical weathering breaks down rock by
changing its chemical composition.
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Chapter 21
Section 4 Weathering and
Erosion
Mechanical Weathering
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Chapter 21
Section 4 Weathering and
Erosion
Chemical Weathering
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Chapter 21
Section 4 Weathering and
Erosion
Physical Weathering
• Ice can break rocks.
• A common kind of mechanical weathering is called
frost wedging.
• Water seeps into cracks or joints in rock and
then freezes.
• When water freezes it expands, pushing rock
apart.
• Every time the ice thaws and refreezes, it
wedges farther into the rock.
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Chapter 21
Section 4 Weathering and
Erosion
Physical Weathering, continued
• Plants can also break rocks.
• The roots of plants can also act as wedges as the
roots grow into cracks in the rocks.
• As the plant grows, the roots exert constant
pressure on the rock, eventually causing pieces to
break off.
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Chapter 21
Section 4 Weathering and
Erosion
Chemical Weathering
• Some minerals react with oxygen, forming oxides.
• Carbon dioxide can cause chemical weathering.
• Carbon dioxide can react with water in the air to form
carbonic acid. This weak acid reacts with some
minerals.
• Minerals dissolved by carbonic acid may be washed
away, leaving underground pockets, or caves.
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Chapter 21
Section 4 Weathering and
Erosion
Chemical Weathering, continued
• Water plays a key role in chemical weathering.
• Some minerals react with water, which changes
their physical properties.
• Some minerals dissolve in water and are carried
to new locations.
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Chapter 21
Section 4 Weathering and
Erosion
Chemical Weathering, continued
• Acid precipitation can slowly dissolve minerals.
• Sulfur dioxide and nitrogen oxides enter the air as
a result of burning fossil fuels.
• These chemicals can react with water in the air,
forming sulfuric acid, nitric acid, or nitrous acid.
• When this happens, the precipitation that results is
acidic.
• Acid Rain Control Program required power plants
to reduce the release of sulfur dioxide, which has
reduced the acidity of rain.
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Chapter 21
Section 4 Weathering and
Erosion
Acid Precipitation
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Chapter 21
Section 4 Weathering and
Erosion
Erosion
• Erosion a process in which the materials of the
Earth’s surface are loosened, dissolved, or worn
away and transported from one place to another by a
natural agent, such as wind, water, ice, or gravity
• Deposition the process in which material such as
sediment is laid down, or deposited as a result of
erosion
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Chapter 21
Section 4 Weathering and
Erosion
Erosion, continued
• Water erosion shapes Earth’s surface.
• Water is the most effective physical weathering
agent.
• Rivers carry sediment to the ocean, and create
canyons and riverbeds.
• The faster the water flows, the larger the sediment it
can carry.
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Chapter 21
Section 4 Weathering and
Erosion
Erosion, continued
• Oceans also shape Earth.
• Waves crash onto shores, shaping the land.
• Ocean waves can create tall cliffs and jagged
coastlines.
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Chapter 21
Section 4 Weathering and
Erosion
Erosion, continued
• Glaciers erode mountains.
• Large masses of ice can exert tremendous forces
on rocks.
• Glaciers can carve U-shaped valleys in
mountains.
• Moving glaciers grind rocks below them into fine
powder.
• Glacial meltwater streams carry the sediment
away from the glacier.
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Chapter 21
Section 4 Weathering and
Erosion
Erosion, continued
• Wind can also shape the landscape.
• Fast moving wind can carry fine sediment.
• Sediment carried by wind can smooth Earth’s
surface and erode the landscape.
• Wind erosion can play a part in forming sandstone
arches
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Chapter 21
Section 4 Weathering and
Erosion
Erosion, continued
One theory to explain the formation of arches is shown below.
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Chapter 21
Section 4 Weathering and
Erosion
Erosion
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Chapter 21
Section 4 Weathering and
Erosion
Concept
Mapping
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Chapter 21
Standardized Test Prep
Understanding Concepts
1. Which of these occurs where two tectonic plates
move away from each other?
A.
B.
C.
D.
convergent boundary
divergent boundary
ocean trench
subduction zone
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
1. Which of these occurs where two tectonic plates
move away from each other?
A.
B.
C.
D.
convergent boundary
divergent boundary
ocean trench
subduction zone
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
2. What causes earthquakes along the San Andreas
fault in California?
F. subduction of the Pacific plate by the North
American plate
G. collision between the Pacific plate and the North
American plate
H. divergent movement of the Pacific plate and the
North American plate
I. horizontal movement along the boundary of the
Pacific plate and the North American plate
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
2. What causes earthquakes along the San Andreas
fault in California?
F. subduction of the Pacific plate by the North
American plate
G. collision between the Pacific plate and the North
American plate
H. divergent movement of the Pacific plate and the
North American plate
I. horizontal movement along the boundary of the
Pacific plate and the North American plate
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
3. How can the absolute age of a layer of rock be
determined?
A. by the principle of superposition
B. by the ratio of radioisotopes
C. by the amount of weathering that has shaped the
rock
D. by analysis of the types of minerals that make up
the rock
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
3. How can the absolute age of a layer of rock be
determined?
A. by the principle of superposition
B. by the ratio of radioisotopes
C. by the amount of weathering that has shaped the
rock
D. by analysis of the types of minerals that make up
the rock
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
4. Which of the following is an example of chemical
weathering of rock?
F.
G.
H.
I.
deposition
erosion
frost wedging
leaching
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
4. Which of the following is an example of chemical
weathering of rock?
F.
G.
H.
I.
deposition
erosion
frost wedging
leaching
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
5. Both S waves and P waves travel from the site of an
earthquake. How does the difference in the way
these waves travel reveal information about the
structure of Earth’s interior?
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Chapter 21
Standardized Test Prep
Understanding Concepts, continued
5. Both S waves and P waves travel from the site of an
earthquake. How does the difference in the way
these waves travel reveal information about the
structure of Earth’s interior?
Answer: S waves cannot pass through liquid. The fact
that P waves can be detected on the opposite side
of the planet, and S waves cannot, indicates a liquid
core.
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Chapter 21
Standardized Test Prep
Reading Skills
In 1912 Alfred Wegener first proposed the theory that all of the
continents formed when one giant continent broke apart. Wegener
used the shape of the continents, the distribution of fossils, and
similarity of rocks at different parts of the world as evidence.
Wegener’s Continental Drift theory was not immediately
accepted by scientists. Some wondered about, but could not find,
forces that would be strong enough to move such large masses of
solid rock over great distances. In the middle of the 20th century,
evidence from ocean floor exploration provided new evidence that
continents move. The theory of plate tectonics, which explains how
land masses move, not across the ocean floor, but across the Earth’s
mantle, is now widely accepted.
6. Why do most scientists now accept the idea of moving
continents, even though earlier scientists did not?
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Chapter 21
Standardized Test Prep
Reading Skills, continued
6. [See previous slide for question.]
Answer: New observations provided evidence that was
not available in 1912. These observations explain
how continents can move and support the theory.
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Chapter 21
Standardized Test Prep
Interpreting Graphics
7. What type of volcano is illustrated here?
A. cinder cone
B. composite
C. seamount
D. shield
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Chapter 21
Standardized Test Prep
Interpreting Graphics, continued
7. What type of volcano is illustrated here?
A. cinder cone
B. composite
C. seamount
D. shield
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