Title: Chapter Menu
1Chapter Menu
Chapter Introduction Lesson 1 The Continental
Drift Hypothesis Lesson 2 Development of a
Theory Lesson 3 The Theory of Plate
Tectonics Chapter Wrap-Up
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2Chapter Introduction
- What is the scientific theory of plate tectonics?
3Chapter Introduction
Before you begin, decide if you agree or disagree
with each of these statements. As you view this
presentation, see if you change your mind about
any of the statements.
4Chapter Introduction
Do you agree or disagree?
- 1. India has always been north of the equator.
- 2. All the continents once formed one
supercontinent. - 3. The seafloor is flat.
5Chapter Introduction
Do you agree or disagree?
- 4. Volcanic activity occurs only on the seafloor.
- 5. Continents drift across a molten mantle.
- 6. Mountain ranges can form when continents
collide.
6Lesson 1 Reading Guide - KC
The Continental Drift Hypothesis
- What evidence supports continental drift?
- Why did scientists question the continental drift
hypothesis?
7Lesson 1 Reading Guide - Vocab
The Continental Drift Hypothesis
- Pangaea
- continental drift
8Lesson 1-1
Pangaea
- Nearly 100 years ago, Alfred Wegener proposed
that all the continents were once part of a
supercontinent called Pangaea. - Over time, Pangaea began breaking apart and the
continents slowly moved to their present position.
9Lesson 1-1
Pangaea (cont.)
- Wegener proposed the hypothesis of continental
drift, which suggested that continents are in
constant motion on the surface of Earth. - Wegener observed the similarities of continental
coastlines now separated by oceans and how they
could fit together like pieces of a puzzle.
10Lesson 1-2
- The eastern coast of South America mirrors the
shape of the west coast of Africa.
11Lesson 1-2
Evidence That Continents Move
- Evidence to support Wegeners hypothesis is found
in - climate clues
- fossil clues
- rock clues.
- When Wegener pieced Pangaea together, he proposed
that the continents were located closer to the
South Pole 250 million years ago.
12Lesson 1-2
Evidence That Continents Move (cont.)
- Wegener suggested that a large sheet of ice
covered the continents. - Wegener studied the sediments left behind and the
glacial grooves that formed when the ice sheets
melted and Pangaea spread apart. - This provided climate evidence for continental
drift.
13Lesson 1-2
- The presence of an ice sheet covering Pangea
could explain glacial features found on some
continents today.
14Lesson 1-2
Evidence That Continents Move (cont.)
- Animals and plants that live on separate
continents can be unique to that continent alone. - Fossils of similar organisms have been found on
several continents separated by oceans. - Fossils of a plant called Glossopteris have been
found on continents that are now separated by
oceans.
15Lesson 1-2
- The orange area shows where fossils of
Glossopteris have been found. - Fossils provide evidence for continental drift.
16Lesson 1-2
Evidence That Continents Move (cont.)
- Wegener observed that mountain ranges and rock
formations on different continents had common
origins, providing rock evidence for continental
drift. - Volcanic rock that is identical in chemistry and
age has been found on both the western coast of
Africa and the eastern coast of South America.
17Lesson 1-2
- The Caledonia mountain range in northern Europe
and the Appalachian Mountains in eastern North
America are similar in age, structure, and rock
type.
18Lesson 1-2
Evidence That Continents Move (cont.)
How were similar rock types used to support the
continental drift hypothesis?
19Lesson 1-3
What was missing?
- Wegeners ideas were not widely accepted until
nearly four decades later. - Scientists questioned continental drift because
it was a slow process and Wegener could not
measure how fast continents moved or how they
moved. - Scientists could not understand how continents
could push their way through the solid rock of
the mantle and the seafloor.
20Lesson 1-3
What was missing? (cont.)
mantle Science Use the middle layer of Earth,
situated between the crust above and the core
below Common Use a loose, sleeveless garment worn
over other clothes
21Lesson 1-3
What was missing? (cont.)
Why did scientists argue against Wegeners
continental drift hypothesis?
22Lesson 1 - VS
- All continents were once part of a supercontinent
called Pangaea.
23Lesson 1 - VS
- Alfred Wegener proposed that continents move
around on Earths surface.
24Lesson 1 LR1
What term did Wegener use to describe the
constant motion of continents on the surface of
Earth?
A. Pangaea B. continental drag C. continental
movement D. continental drift
25Lesson 1 LR2
In which of these did Wegener observe
similarities that suggested continents might fit
together like the pieces of a puzzle?
A. fossils B. ice sheets C. plates D. continental
coastlines
26Lesson 1 LR3
Wegener proposed that 250 million years ago,
South America, Africa, India, and Australia were
located closer to what?
A. equator B. South Pole C. North Pole D. Pacific
ocean
27Lesson 1 - Now
Do you agree or disagree?
- 1. India has always been north of the equator.
- 2. All the continents once formed one
supercontinent.
28Lesson 2 Reading Guide - KC
Development of a Theory
- What is seafloor spreading?
- What evidence is used to support seafloor
spreading?
29Lesson 2 Reading Guide - Vocab
Development of a Theory
- mid-ocean ridge
- seafloor spreading
- normal polarity
- magnetic reversal
- reversed polarity
30Lesson 2-1
Mapping the Ocean Floor
- During the late 1940s scientists were able to
determine the depth of the ocean using a device
called an echo sounder. - Once ocean depths were determined, scientists
used these data to create a topographic map of
the sea floor that revealed vast mountain ranges,
called mid-ocean ridges, that stretch for many
miles deep below the oceans surface.
31Lesson 2-1
Seafloor Topography
32Lesson 2-2
Seafloor Spreading
- By the 1960s, scientists discovered the process
of seafloor spreading. - Seafloor spreading is the process by which new
oceanic crust forms along a mid-ocean ridge and
older oceanic crust moves away from the ridge. - When the seafloor spreads, the mantle below melts
and forms magma.
33Lesson 2-2
Seafloor Spreading (cont.)
- Magma erupts on Earths surface as lava, which
cools and crystallizes on the seafloor, forming
rock. - Because the lava erupts into water, it cools
rapidly and forms rounded structures called
pillow lavas. - As the seafloor continues to spread apart, the
older oceanic crust moves away from the mid-ocean
ridge.
34Lesson 2-2
Seafloor Spreading (cont.)
35Lesson 2-2
Seafloor Spreading (cont.)
- Scientists argued that if the seafloor spreads,
the continents must also be moving.
What is seafloor spreading?
36Lesson 2-2
Seafloor Spreading (cont.)
- The rugged mountains that make up the mid-ocean
ridge system can form in two different ways. - Large amounts of lava can erupt from the center
of the ridge, cool, and build up around the ridge.
37Lesson 2-2
Seafloor Spreading (cont.)
- Or, as the lava cools and forms new crust, it
cracks and the rocks move up or down along these
cracks in the seafloor, forming jagged mountain
ranges. - The abyssal plain, the smooth part of the
seafloor, is made when the layer of sediment that
accumulates far from the mid-ocean ridge becomes
thick enough.
38Lesson 2-2
- Continents move as the seafloor spreads along a
mid-ocean ridge.
39Lesson 2-3
Development of a Theory
- The first evidence used to support seafloor
spreading was discovered in rocks on the
seafloor. - Scientists studied the magnetic signature of
minerals in these rocks. - Earths magnetic field today is described as
having normal polaritya state in which
magnetized objects, such as compass needles, will
orient themselves to point north.
40Lesson 2-3
Development of a Theory (cont.)
- Sometimes a magnetic reversal occurs and the
magnetic field reverses direction. - The opposite of normal polarity is reversed
polarity a state in which magnetized objects
reverse direction and orient themselves to point
south.
41Lesson 2-3
42Lesson 2-3
Development of a Theory (cont.)
- Volcanic rock on the seafloor contains iron-rich
minerals that are magnetic. - Magnetic minerals in cooling lava from the
mid-ocean ridge record the direction of Earths
magnetic field. - Scientists have discovered parallel patterns in
the magnetic signature of rocks on either side of
a mid-ocean ridge.
43Lesson 2-3
- Minerals in fresh lava record Earths magnetic
signature.
44Lesson 2-3
Development of a Theory (cont.)
- Scientists studied magnetic minerals in rocks
from the seafloor using a magnetometer to measure
and record the magnetic signature. - They discovered parallel magnetic stripes on
either side of the mid-ocean ridge.
45Lesson 2-3
Development of a Theory (cont.)
- Each pair of stripes has a similar composition,
age, and magnetic character. - The pairs of magnetic stripes confirm that the
ocean crust formed at mid-ocean ridges is carried
away from the center of the ridges in opposite
directions.
46Lesson 2-3
Seafloor Spreading Theory
47Lesson 2-3
Development of a Theory (cont.)
- Other measurements made on the seafloor confirm
seafloor spreading. - Measuring the amount of thermal energy leaving
the Earth shows that more thermal energy leaves
Earth near mid-ocean ridges than is released from
beneath the abyssal plains.
48Lesson 2-3
Development of a Theory (cont.)
- Sediment collected from the seafloor can be dated
to show that the sediment closest to the
mid-ocean ridge is younger than the sediment
farther away from the ridge.
49Lesson 2 - VS
- New ocean crust forms along mid-ocean ridges.
- Mid-ocean ridges are large mountain ranges that
extend throughout Earths oceans.
50Lesson 2 - VS
- A magnetic reversal occurs when Earths magnetic
field changes direction.
51Lesson 2 LR1
As the seafloor continues to spread apart, the
older oceanic crust moves in which direction with
respect to the mid-ocean ridge?
A. toward it B. above it C. away from it D. under
it
52Lesson 2 LR2
Todays magnetic field is described as having
which of these?
A. reversed polarity B. normal polarity C. magneti
c reversal D. no polarity
53Lesson 2 LR3
In which state do magnetized objects reverse
themselves to point south?
A. reversed polarity B. normal polarity C. seafloo
r spreading D. magnetic polarity
54Lesson 2 - Now
Do you agree or disagree?
3. The seafloor is flat. 4. Volcanic activity
occurs only on the seafloor.
55Lesson 3 Reading Guide - KC
The Theory of Plate Tectonics
- What is the theory of plate tectonics?
- What are the three types of plate boundaries?
- Why do tectonic plates move?
56Lesson 3 Reading Guide - Vocab
The Theory of Plate Tectonics
- plate tectonics
- lithosphere
- divergent plate boundary
- transform plate boundary
- convergent plate boundary
57Lesson 3 Reading Guide - Vocab
The Theory of Plate Tectonics
- subduction
- convection
- ridge push
- slab pull
58Lesson 3-1
The Plate Tectonics Theory
- The theory of plate tectonics, proposed in the
late 1960s, states that Earths surface is made
of rigid slabs of rock, or plates, that move with
respect to each other. - Plate tectonics suggests that Earths surface is
divided into large plates of rigid rock and each
plate moves over Earths hot and semiplastic
mantle.
59Lesson 3-1
The Plate Tectonics Theory (cont.)
What is plate tectonics?
60Lesson 3-1
The Plate Tectonics Theory (cont.)
- Geologists use the word tectonic to describe the
forces that shape Earths surface and the rock
structures that form as a result. - The cold and rigid outermost rock layer of the
Earth is called the lithosphere. - The lithosphere is made up of the crust and the
solid, uppermost mantle.
61Lesson 3-1
Earths Tectonic Plates
62Lesson 3-1
The Plate Tectonics Theory (cont.)
- The lithosphere is thin below mid-ocean ridges
and thick below continents. - Earths tectonic plates are large pieces of the
lithosphere that fit together like the pieces of
a giant jigsaw puzzle. - The layer of Earth below the lithosphere, called
the asthenosphere, is so hot that it behaves like
a plastic material and enables Earths plates to
move.
63Lesson 3-2
The Plate Tectonics Theory (cont.)
plastic Science Use capable of being molded or
changing shape without breaking Common Use any of
numerous organic, synthetic, or processed
materials made into objects
64Lesson 3-2
Plate Boundaries
- A divergent plate boundary forms where two plates
separate. - When the seafloor spreads at a mid-ocean ridge,
lava erupts, cools, and forms new oceanic crust. - Divergent plate boundaries can also exist in the
middle of a continent, where they pull continents
apart and form rift valleys.
65Lesson 3-3
66Lesson 3-2
Plate Boundaries (cont.)
- A transform plate boundary forms where two plates
slide past each other. - As they move past one another, the plates can get
stuck and stop moving. - Stress builds up where the plates are stuck until
they eventually break and suddenly move apart,
resulting in a rapid release of energy as
earthquakes.
67Lesson 3-3
68Lesson 3-2
Plate Boundaries (cont.)
- Convergent plate boundaries form where two plates
collide. - The denser plate sinks below the more buoyant
plate in a process called subduction. - The area where a denser plate descends into Earth
along a convergent plate boundary is called a
subduction zone.
69Lesson 3-2
Plate Boundaries (cont.)
subduction from Latin subductus, means to lead
under, removal
70Lesson 3-2
Plate Boundaries (cont.)
- When an oceanic plate and a continental plate
collide, the denser oceanic plate subducts under
the edge of the continent, creating a deep ocean
trench and a line of volcanoes above the
subducting plate on the edge of the continent. - When two continental plates collide, neither
plate is subducted, and mountains form from
uplifted rock.
71Lesson 3-3
72Lesson 3-3
73Lesson 3-2
Plate Boundaries (cont.)
What are the three types of plate boundaries?
74Lesson 3-3
Evidence for Plate Tectonics
- Scientists can measure how fast continents move
using a network of satellites called the Global
Positioning System. - Because plates are rigid, tectonic activity
occurs where plates meet.
75Lesson 3-3
Evidence for Plate Tectonics (cont.)
- Volcanoes form where plates separate along a
mid-ocean ridge or continental rift or collide
along a subduction zone. - Mountains can form where two continents collide.
76Lesson 3-3
- Notice the relationship between earthquake
epicenters, volcanoes, and plate boundaries.
77Lesson 3-3
Evidence for Plate Tectonics (cont.)
How are earthquakes and volcanoes related to the
theory of plate tectonics?
78Lesson 3-4
Plate Motion
- Earths plates move because the asthenosphere
moves underneath the lithosphere. - Convection is the circulation of material caused
by differences in density. - Hot mantle material rises upward and comes in
contact with Earths crust.
79Lesson 3-4
Plate Motion (cont.)
- As the mantle cools, it becomes denser and then
sinks, forming a convection current. - Convection currents in the asthenosphere act like
a conveyor belt moving the lithosphere above it. - There are three forces that interact to cause
plate motion basal drag, ridge push, and slab
pull.
80Lesson 3-4
Plate Motion (cont.)
What causes convection?
81Lesson 3-4
Plate Motion (cont.)
- Basal drag refers to how convection currents in
the asthenosphere circulate and drag the
lithosphere like a conveyor belt. - Rising mantle material at mid-ocean ridges
creates the potential for plates to move away
from the ridge with a force called ridge push.
82Lesson 3-4
- As a slab, or dense plate, sinks, it pulls on the
rest of the plate with a force called slab pull.
83Lesson 3-5
A Theory in Progress
- Plate tectonics has become the unifying theory of
geology, but several unanswered questions remain. - Why is Earth the only planet in the solar system
that has plate tectonic activity? - Why do some earthquakes and volcanoes occur far
away from plate boundaries?
84Lesson 3-5
- What forces dominate plate motion?
- What will scientists study next? This is a 3-D
image of seismic wave velocities from a new
technique called anisotropy.
85Lesson 3 - VS
- Tectonic plates are made of cold and rigid
slabs of rock. - Mantle convectionthe circulation of mantle
material due to density differencesdrives plate
motion.
86Lesson 3 - VS
- The three types of plate boundaries are
divergent, convergent, and transform boundaries.
87Lesson 3 LR1
What word do geologists use to describe the
forces that shape Earths surface?
A. semiplastic B. lithosphere C. tectonic D. mantl
e
88Lesson 3 LR2
Which of these is made up of the crust and the
solid, uppermost mantle?
A. seafloor B. lithosphere C. biosphere D. hydrosp
here
89Lesson 3 LR3
What type of boundary forms where two plates
separate?
A. convergent plate boundary B. transform plate
boundary C. new plate boundary D. divergent plate
boundary
90Lesson 3 - Now
Do you agree or disagree?
5. Continents drift across a molten
mantle. 6. Mountain ranges can form when
continents collide.
91Chapter Review Menu
Key Concept Summary Interactive Concept
Map Chapter Review Standardized Test Practice
92The BIG Idea
- The scientific theory of plate tectonics states
that Earths lithosphere is broken up into rigid
plates that move over Earths surface.
93Key Concepts 1
Lesson 1 The Continental Drift Hypothesis
- The puzzle piece fit of continents, fossil
evidence, climate, rocks, and mountain ranges
supports the hypothesis of continental drift. - Scientists were skeptical of continental drift
because Wegener could not explain the mechanism
for movement.
94Key Concepts 2
Lesson 2 Development of a Theory
- Seafloor spreading provides a mechanism for
continental drift. - Seafloor spreading occurs at mid-ocean ridges.
- Evidence of magnetic reversal in rock, thermal
energy trends, and the discovery of seafloor
spreading all contributed to the development
of the theory of plate tectonics.
95Key Concepts 3
Lesson 3 The Theory of Plate Tectonics
- Types of plate boundaries, the location of
earthquakes, volcanoes, and mountain ranges, and
satellite measurement of plate motion support the
theory of plate tectonics. - Mantle convection, ridge push, and slab pull are
the forces that cause plate motion.
Radioactivity in the mantle and thermal energy
from the core produce the energy for convection.
96Chapter Review MC1
Which of these have been found on several
continents separated by oceans, suggesting that
they were once geographically closer together?
A. animals B. ice sheets C. plant fossils
D. plate boundaries
97Chapter Review MC2
Which of these refers to the process by which new
oceanic crust forms along a mid-ocean ridge as
older oceanic crust moves away from the ridge?
A. continental drift B. plate tectonics C. seafloo
r spreading D. magnetic reversal
98Chapter Review MC3
What is the rigid outermost layer of Earth called?
A. mantle B. lithosphere C. plate D. transform
plate boundary
99Chapter Review MC4
What forms where two plates slide past each other?
A. transform plate boundary B. divergent plate
boundary C. convergent plate boundary D. semiplast
ic mantle
100Chapter Review MC5
What is the process in which a denser plate sinks
below a more buoyant plate?
A. seafloor spreading B. convergence C. convection
D. subduction
101Chapter Review STP1
What is the name of the supercontinent that all
continents were once part of?
A. Wegener B. Pangaea C. mantle D. seafloor
102Chapter Review STP2
Where did scientists find glacial features that
are usually associated with cooler climates?
A. Antarctica B. plate boundaries C. mountain
ranges D. Africa
103Chapter Review STP3
Which term refers to vast mountain ranges on the
seafloor?
A. volcanoes B. oceanic crust C. pillow
lava D. mid-ocean ridges
104Chapter Review STP4
Which of these states that Earths surface is
made of rigid slabs of rock that move with
respect to one another?
A. the theory of plate tectonics B. the theory of
mid-ocean ridges C. the theory of divergent plate
boundaries D. the theory of transform plate
boundaries
105Chapter Review STP5
What is the name for the force that pulls on the
rest of a plate as part of a dense plate sinks?
A. ridge push B. basal drag C. slab pull D. plate
tectonics