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Plate Tectonics
Table of Contents
Earth’s Interior
Convection and the Mantle
Drifting Continents
Sea-Floor Spreading
The Theory of Plate Tectonics
Plate Tectonics - Earth’s Interior
Exploring Inside the Earth
Geologists have used two main types of
evidence to learn about Earth’s interior: direct
evidence from rock samples and indirect
evidence from seismic waves.
Plate Tectonics - Earth’s Interior
The Crust
The crust is a layer of solid
rock that includes both dry
land and the ocean floor.
Plate Tectonics - Earth’s Interior
The Mantle
Earth’s mantle is made up of rock that is very hot, but solid.
Scientists divide the mantle into layers based on the physical
characteristics of those layers.
Plate Tectonics
Lithosphere and Asthenosphere
The Lithosphere and Asthenosphere are two
layers of the Mantle.
Lithosphere (Litho means Stone in Greek) is the
solid rocky upper layer of the mantle. It’s about
100 km (60 miles) thick on average.
Asthenosphere (Asthenes means “Weak” in
Greek) below the lithosphere this layer is softer
and flows very slowly.
Plate Tectonics - Earth’s Interior
The Core and magnetic field.
The core is made mostly of the metals iron and nickel. It
consists of two parts–a liquid outer core and a solid inner
core. The movement of these layers over each other is what
makes the Earth’s magnetic field.
Plate Tectonics
Plate Tectonics
The Earths’
Magnetosphere
Plate Tectonics - Earth’s Interior
Temperature Inside the Earth
The graph shows how
temperatures change between
Earth’s surface and the bottom
of the mantle. On this graph the
temperature at the Earth’s
surface is 0oC. Study the graph
carefully and then answer the
questions.
Plate Tectonics - Earth’s Interior
Temperature Inside the Earth
Reading Graphs:
As you move from left to right
on the x-axis, how does depth
inside the Earth change?
The depth increases.
Plate Tectonics - Earth’s Interior
Temperature Inside the Earth
Estimating:
What is the temperature at
the boundary between the
lithosphere and the
asthenosphere?
About 1,600oC
Plate Tectonics - Earth’s Interior
Temperature Inside the Earth
Estimating:
What is the temperature at
the boundary between the
lower mantle and the core?
About 3,200oC
Plate Tectonics - Earth’s Interior
Temperature Inside the Earth
Interpreting Data:
How does temperature
change with depth in Earth’s
interior?
It generally increases with
depth.
Plate Tectonics - Earth’s Interior
Using Prior Knowledge
Before you read, look at the section headings and visuals to
see what this section is about. Then write what you know
about Earth’s interior in a graphic organizer like the one
below. As you read, write what you learn.
What You Know
1.
2.
3.
4.
5.
Earth’s crust is made of rock.
Earth is very hot near the center.
Dry land is part of the crust.
The mantle is very hot.
The core contains iron.
What You Learned
1.
2.
3.
4.
5.
Geologists use seismic waves to study Earth’s interior.
Radioactive substances heat the interior of Earth.
The crust is thickest under high mountains.
The mantle is solid.
Movements in the outer core create Earth’s magnetic field.
Plate Tectonics - Earth’s Interior
Links on the Structure of Earth
Click the SciLinks button for links on the structure of Earth.
Plate Tectonics
End of
Section:
Earth’s Interior
Plate Tectonics - Convection and the Mantle
Types of Heat Transfer
There are three types of heat transfer: radiation, conduction,
and convection.
Plate Tectonics - Convection and the Mantle
Convection Currents
Heating and cooling of the fluid, changes in the fluid’s
density, and the force of gravity combine to set convection
currents in motion.
Plate Tectonics - Convection and the Mantle
Convection Currents in Earth
Heat from the core and the mantle itself causes convection
currents in the mantle. This is believed to power Plate
Tectonics -
Video
clip
Plate Tectonics - Convection and the Mantle
Outlining
An outline shows the
relationship between major
ideas and supporting ideas.
As you read, make an outline
about heat transfer. Use the
red headings for the main
topics and the blue headings
for the subtopics.
Convection and the Mantle
I. Types of Heat Transfer
A. Radiation
B. Conduction
C. Convection
II. Convection Currents
III. Convection in Earth’s Mantle
Plate Tectonics - Convection and the Mantle
More on Convection Currents in the Mantle
Click the PHSchool.com button for an activity about
convection currents in the mantle.
Plate Tectonics - Convection and the Mantle
Mantle Convection
Click the Video button to watch a movie
about mantle convections.
Plate Tectonics
End of
Section:
Convection
and the Mantle
Plate Tectonics - Drifting Continents
Continental Drift
Wegener’s hypothesis was that all the continents were once
joined together in a single landmass.
Plate Tectonics - Drifting Continents
Evidence for Continental Drift
Fossils and rocks found on different continents provide
evidence that Earth’s landmasses once were joined together
in the supercontinent Pangaea.
Plate Tectonics - Drifting Continents
Evidence for Continental Drift
Fossils and rocks found on different continents provide
evidence that Earth’s landmasses once were joined together
in the supercontinent Pangaea.
Plate Tectonics - Drifting Continents
Identifying Supporting Evidence
As you read, identify the evidence that supports the
hypothesis of continental drift. Write the evidence in a
graphic organizer like the one below.
Evidence
Shape of
continents
Hypothesis
Earth’s continents
have moved.
Fossils
Climate
change
Plate Tectonics - Drifting Continents
Links on Continental Drift
Click the SciLinks button for links on continental drift.
Plate Tectonics
End of
Section:
Drifting
Continents
Plate Tectonics - Sea-Floor Spreading
Mid-Ocean Ridges
The East Pacific Rise is just one of the many mid-ocean
ridges that wind beneath Earth’s oceans.
Plate Tectonics - Sea-Floor Spreading
What Is Sea-Floor Spreading?
In sea-floor spreading, the sea floor spreads apart along both
sides of a mid-ocean ridge as new crust is added. As a
result, the ocean floors move like conveyor belts, carrying the
continents along with them.
Plate Tectonics - Sea-Floor Spreading
Evidence for Sea-Floor Spreading
Several types of evidence supported Hess’s theory
of sea-floor spreading: eruptions of molten
material, magnetic stripes in the rock of the ocean
floor, and the ages of the rocks themselves.
Plate Tectonics - Sea-Floor Spreading
Subduction at Trenches
In a process taking tens of millions of years, part of the
ocean floor sinks back into the mantle through deep-ocean
trenches. (where is the oldest rock found?)
Plate Tectonics - Sea-Floor Spreading
Growing an Ocean
Because of sea-floor spreading, the distance between
Europe and North America is increasing by a few centimeters
per year.
Plate Tectonics - Sea-Floor Spreading
Sequencing
Make a flowchart to show the process of sea-floor spreading.
Magma erupts along mid-ocean ridge.
Magma cools to form new sea floor.
Sea floor spreads away from ridge.
Plate Tectonics - Sea-Floor Spreading
More on Sea-Floor Spreading
Click the PHSchool.com button for an activity about
sea-floor spreading.
Plate Tectonics - Sea-Floor Spreading
Sea-Floor Spreading
Click the Video button to watch a movie
about sea-floor spreading.
Plate Tectonics
End of Section:
Sea-Floor
Spreading
Plate Tectonics - The Theory of Plate Tectonics
How Plates Move
The theory of plate tectonics explains the formation,
movement, and subduction of Earth’s plates.
Plate Tectonics - The Theory of Plate Tectonics
Plate Boundaries
There are three kinds of plate boundaries: divergent
boundaries, convergent boundaries, and transform
boundaries. A different type of plate movement occurs along
each type of boundary. Pages 34 and 35 in text.
Plate Tectonics - The Theory of Plate Tectonics
Calculating a Rate
To calculate the rate of plate motion, divide the distance
the plate moves by the time it takes to move that
distance.
Rate = distance/time
For example, a plate takes two million years to move
156 km. Calculate its rate of motion.
156 km/2,000,000 years = 7.8 cm per year
Practice Problem
The Pacific plate is sliding past the North American
plate. It has take ten million years for the plate to move
600 km. What is the Pacific plate’s rate of motion?
60,000,000 cm ÷ 10,000,000 years = 6 cm/yr
Plate Tectonics - The Theory of Plate Tectonics
Continental Drift
It has taken the continents about 225 million years since the
breakup of Pangaea to move to their present locations.
Plate Tectonics - The Theory of Plate Tectonics
Continental Drift Activity
Click the Active Art button to open a browser window and
access Active Art about continental drift.
Plate Tectonics - The Theory of Plate Tectonics
Building Vocabulary
A definition states the meaning of a word or phrase by telling
about its most important feature or function. After you read
the section, reread the paragraphs that contain definitions of
Key Terms. Use all the information you have learned to write
a definition of each Key Term in your own words.
Key Terms:
Examples:
plate
divergent
boundary
The place
lithosphere
whereistwo
broken
plates
into
move
separate
apart,sections
or diverge,
called
is
plates.a divergent boundary.
called
scientific
rift valley theory
A
well-tested
concept
A scientific
deep valleytheory
calledisa arift
valley forms
alongthat
the
explains
wide range of observations.
divergentaboundary.
The theory of plate tectonics states that pieces of
The place where two plates come together, or
Earth’s lithosphere are in slow, constant motion, driven
converge, is called a convergent boundary.
by convection currents in the mantle.
A
transform
boundary
is a place
where rocks
two plates
Faults
are breaks
in Earth’s
crust where
have
slip
pastpast
each
other,
moving in opposite directions.
slipped
each
other.
plate tectonics
convergent boundary
transform
boundary
fault
Plate Tectonics
End of Section:
The Theory of
Plate Tectonics
Plate Tectonics
Graphic Organizer
Type of Plate
Boundary
Type of Motion
Effect on
Crust
Feature(s)
Formed
Transform
boundary
Plates slide past
each other.
Crust is sheared.
Strike-slip fault
Convergent
boundary
Plates move
together.
Subduction or
mountain building
Mountains,
volcanoes
Divergent
boundary
Plates move
apart.
Crust pulled apart
by tension forces.
Mid-ocean ridge,
ocean floor
Plate Tectonics
End of Section:
Graphic Organizer