Download Section 1 Inside the Earth Chapter 15 Tectonic Plates, continued A

Chapter 15
Plate Tectonics
Preview
Section 1 Inside the Earth
Section 2 Restless Continents
Section 3 The Theory of Plate Tectonics
Section 4 Deforming the Earth’s Crust
Concept Mapping
Chapter 15
Section 1 Inside the Earth
Question of the Day
If you journeyed to the center of the Earth, what do
you think you would see along the way?
Draw an illustration of the journey for your QOD.
Chapter 15
Section 1 Inside the Earth
Objectives
• Identify the layers of the Earth by their chemical
composition.
• Identify the layers of the Earth by their physical
properties.
• Describe a tectonic plate.
• Explain how scientists know about the structure of
Earth’s interior.
Chapter 15
Section 1 Inside the Earth
The Composition of the Earth
• The Earth is divided into three layers.
•Crust
•Mantle
•Core
• Crust - the thin and solid outermost layer of the
Earth above the mantle.
•Crust is 5 to 100 km thick, and is the thinnest layer
of the Earth.
Chapter 15
Section 1 Inside the Earth
The Composition of the Earth, continued
• Two types of crust—continental (land) and
oceanic (ocean).
•Oceanic crust is thinner and denser than
continental crust.
Chapter 15
Section 1 Inside the Earth
The Composition of the Earth, continued
• Mantle - the layer of rock between the Earth’s
crust and core.
•The mantle is much thicker than the crust, it makes
up about 2/3 of Earth.
• We have never dug down that deep, so scientists
must draw conclusions about what the mantle is
made of and other physical properties from the
Earth’s surface.
Chapter 15
Section 1 Inside the Earth
The Composition of the Earth, continued
•Core - the central part of the Earth below the
mantle.
•The core makes up about one-third of Earth’s
mass.
• Scientists think that the Earth’s core is made
mostly of iron.
Chapter 15
Section 1 Inside the Earth
Chapter 15
Section 1 Inside the Earth
The Physical Structure of the Earth
The Earth is divided into five physical layers:
1.
2.
3.
4.
5.
The lithosphere
The asthenosphere
The mesosphere
The outer core
The inner core
Each layer has its own set of physical properties.
Chapter 15
Section 1 Inside the Earth
Physical Structure of the Earth,
continued
• Lithosphere – the solid, outer layer of the Earth that
consists of the crust and the rigid upper part of the
mantle.
• The lithosphere is divided into pieces that are called
tectonic plates.
Chapter 15
Section 1 Inside the Earth
Physical Structure of the Earth,
continued
• Asthenosphere - the soft layer of the mantle on
which the tectonic plates move.
• The asthenosphere is made of solid rock that flows
very slowly.
Chapter 15
Section 1 Inside the Earth
Chapter 15
Section 1 Inside the Earth
Physical Structure of the Earth,
continued
• Mesosphere - is the strong, lower part of the
mantle between the asthenosphere and the outer
core.
• The prefix meso- means “middle.”
Chapter 15
Section 1 Inside the Earth
Physical Structure of the Earth,
continued
• Earth’s core is divided into two parts.
• The outer core is liquid and is right under the mantle.
• The inner core is solid iron and is the center of the
Earth.
Chapter 15
Section 1 Inside the Earth
Chapter 15
Section 1 Inside the Earth
Tectonic Plates
• Tectonic Plate – a block of lithosphere that
consists of the crust and the rigid, outermost part of
the mantle.
• These plates make the Earth look covered in puzzle
pieces.
Chapter 15
Section 1 Inside the Earth
Tectonic Plates, continued
• A Giant Jigsaw Puzzle Each tectonic plate fits
together with the tectonic plates that surround it.
• The lithosphere is like a jigsaw puzzle. The tectonic
plates are like the pieces of the puzzle.
Chapter 15
Section 1 Inside the Earth
Tectonic Plates, continued
• A Tectonic Plate Close-Up The following Visual
Concept presentation shows the Earth’s major
tectonic plates and how they fit together.
• The presentation also illustrates what a tectonic
plate might look like if you could lift it out of its place.
Chapter 15
Section 1 Inside the Earth
Tectonic Plates, continued
• Tectonic plates “float” on the asthenosphere.
•The plates bump into one another when they
move.
Chapter 15
Section 1 Inside the Earth
Mapping the Earth’s Interior
•Since we can’t dig in the Earth how do we know
what is there?
•Scientists measure speeds of seismic waves that
travel through the Earth’s interior during
earthquakes.
• By using seismographs, scientists have learned
that the Earth is made of different layers.
Chapter 15
Section 2 Restless Continents
Question of the Day
What is meant by the following statement:
“The United States is moving westward.”
From what you know about geology and plate
tectonics explain if you believe this statement to be
true or false.
Chapter 15
Section 2 Restless Continents
Objectives
• Describe Wegener’s hypothesis of continental drift.
• Explain how sea-floor spreading provides a way for
continents to move.
• Describe how new oceanic lithosphere forms at midocean ridges.
• Explain how magnetic reversals provide evidence for
sea-floor spreading.
Chapter 15
Section 2 Restless Continents
Continental Drift Hypothesis
• Continental drift - the hypothesis that states that
continents once formed a single landmass, broke up,
and drifted to their present locations.
Chapter 15
Section 2 Restless Continents
The Breakup of Pangaea
• It was theorized that all of the present continents
were once joined in a single, huge continent he
called Pangaea.
• Pangaea is Greek for “all earth.”
• Pangaea existed about 245 million years ago.
Chapter 15
Section 2 Restless Continents
Sea-Floor Spreading
• Evidence supporting continental drift hypothesis
comes from sea-floor spreading.
• Sea-floor spreading - the process by which new
oceanic lithosphere forms as magma rises toward
the surface and solidifies.
Chapter 15
Section 2 Restless Continents
Sea-Floor Spreading, continued
•Mid-ocean ridges are underwater mountain chains
that run through Earth’s ocean basins where seafloor spreading takes place.
Chapter 15
Section 2 Restless Continents
Chapter 15
Section 2 Restless Continents
Sea-Floor Spreading, continued
•Some of the most important evidence of sea-floor
spreading comes from magnetic reversals recorded
in the ocean floor.
•Molten rock at the mid-ocean ridge contains tiny
grains of magnetic minerals that act like
compasses.
Chapter 15
Section 2 Restless Continents
Sea-Floor Spreading, continued
• When the Earth’s magnetic field reverses, the
magnetic mineral grains align in the opposite
direction. The new rock records the direction of
the Earth’s magnetic field.
Chapter 15
Section 3 The Theory of Plate Tectonics
Question of the Day
If the sea floor is spreading an average of 4 cm a
year, how many years did it take New York and the
west coast of Africa to reach their current
locations, 6,760 km apart?
Calculate your answer in your science journal.
Chapter 15
Section 3 The Theory of Plate Tectonics
Objectives
• Describe the three types of tectonic plate boundaries.
• Describe the three forces thought to move tectonic
plates.
• Explain how scientists measure the rate at which
tectonic plates move.
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries
• As scientists’ understanding of mid-ocean ridges
and magnetic reversals grew, a theory was formed
to explain how tectonic plates move.
• Plate tectonics is the theory that explains how
large pieces of the Earth’s outermost layer, called
tectonic plates, move and change shape.
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
• A boundary is a place where tectonic plates touch.
•All tectonic plates share boundaries with other
tectonic plates.
• The type of boundary depends on which direction
the tectonic plates move.
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
Three types of boundaries:
Convergent Boundaries
Divergent Boundaries
Transform Boundaries
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
•Convergent boundary – the boundary formed by
the collision of two lithospheric plates.
• What happens at convergent boundaries depends
on the kind of crust at the leading edge of each
tectonic plate.
Chapter 15
Section 3 The Theory of Plate Tectonics
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
•Divergent boundary – the boundary between two
tectonic plates that are moving away from each
other.
• New sea floor forms at divergent boundaries. SeaFloor Spreading.
Chapter 15
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
• Transform boundary – the boundary between
tectonic plates that are sliding past each other
horizontally.
• The San Andreas Fault in California is an example
of a transform boundary.
Chapter 15
Section 3 The Theory of Plate Tectonics
Chapter 15
Section 3 The Theory of Plate Tectonics
Causes of Plate Movement
• What causes the motion of tectonic plates?
•Tectonic plates move because of changes in the
density in the asthenosphere.
• The following Visual Concept presentation
examines three possible driving forces of tectonic
plate motion.
Chapter 15
Section 3 The Theory of Plate Tectonics
Tracking Plate Movement
• Tectonic plate movements are so slow and gradual
that you can’t see or feel them.
•Tectonic plate movement is measured in
centimeters per year.
• Scientists use a system of satellites called the
global positioning system (GPS) to measure the rate
of tectonic plate movement.