Download Unit 4 Lesson 6

Unit 4 Lesson 6 Plate Tectonics
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Unit 4 Lesson 6 Plate Tectonics
Indiana Standards
• 7.2.1 Describe how the earth is a layered
structure composed of lithospheric plates, a
mantle and a dense core.
• 7.2.4 Explain how convection currents in the
mantle cause lithospheric plates to move causing
fast changes like earthquakes and volcanic
eruptions, and slow changes like creation of
mountains and formation of new ocean floor.
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Unit 4 Lesson 6 Plate Tectonics
Puzzling Evidence
What evidence suggests that
continents move?
• In the late 1800s, Alfred Wegener
proposed his hypothesis of
continental drift.
• According to this hypothesis, the
continents once formed a single
landmass, broke up, and drifted.
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Unit 4 Lesson 6 Plate Tectonics
What evidence suggests that
continents move?
• Several lines of evidence
supported Wegener’s hypothesis.
• Fossils of the same species are
found on continents on separate
sides of the Atlantic Ocean.
• The locations of mountain
ranges and rock formations and
evidence of ancient climatic
conditions also supported
Wegner’s hypothesis.
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Unit 4 Lesson 6 Plate Tectonics
What is Pangaea?
• Today, scientists accept that the continents were
once joined.
• About 245 million years ago, the continents were
joined in a single large landmass called Pangaea.
• Over millions of years, Pangaea broke into
fragments that drifted and collided with each other.
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Unit 4 Lesson 6 Plate Tectonics
What is Pangaea?
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Unit 4 Lesson 6 Plate Tectonics
What discoveries support the idea of
continental drift?
• Scientists did not
accept Wegener’s ideas
because they could not
determine how
continents moved.
• In the mid-1900s,
scientists began
mapping the sea floor
and discovered features
that supported some of
Wegener’s ideas.
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Unit 4 Lesson 6 Plate Tectonics
What discoveries support the idea of
continental drift?
• Scientists discovered that oceanic crust is young
compared to continental crust.
• They also discovered that sea floor rock contains
magnetic patterns.
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What discoveries support the
idea of continental drift?
A process called seafloor spreading
explains the age and
magnetic pattern of sea
floor rocks.
Unit 4 Lesson 6 Plate Tectonics
What discoveries support the idea of
continental drift?
• Through sea-floor spreading,
molten rock rises at the
ridges and forms new
oceanic crust.
• Older crust is pushed away
from the ridge, and the sea
floor slowly spreads apart.
• Scientists also discovered
huge trenches in the sea
floor where oceanic crust
sinks into the
asthenosphere.
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Unit 4 Lesson 6 Plate Tectonics
A Giant Jigsaw
What is the theory of plate tectonics?
• Scientists began to form a new theory to explain
how tectonic plates move.
• Plate tectonics is a theory that describes largescale movements of Earth’s lithosphere.
• It describes why and how continents move and
explains how many of the features on Earth’s
crust form.
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Unit 4 Lesson 6 Plate Tectonics
What is a tectonic plate?
• The lithosphere is divided into pieces called
tectonic plates, which move around on top of
the asthenosphere.
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Unit 4 Lesson 6 Plate Tectonics
Boundaries
What are three types of plate
boundaries?
• The three types of plate boundaries are
convergent boundaries, divergent boundaries, and
transform boundaries.
• Each type is associated with characteristic
landforms.
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Unit 4 Lesson 6 Plate Tectonics
What are three types of plate
boundaries?
• Convergent boundaries form where two plates
collide. This can happen in three ways, depending
on the type of crust that is involved.
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Convergent Boundary
Continent-Continent
•Two continental plates
collide
•Plates buckle and thicken
•Forms mountains
Convergent Boundary
Oceanic - Continental
•Oceanic and continental
plates collide
•Oceanic plate sub ducts
because it is denser
•Forms coastal volcanoes
and trenches
Convergent Boundary
Oceanic - Oceanic
•Two oceanic plates collide.
•The older and denser of the
two plates sub ducts under
the younger plate
•Forms volcanic Island arcs
Unit 4 Lesson 6 Plate Tectonics
What are three types of plate
boundaries?
• At a divergent boundary, two plates move away
from each other, and magma forms new
lithosphere at mid-ocean ridges.
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Unit 4 Lesson 6 Plate Tectonics
What are three types of plate
boundaries?
• A boundary at which two plates move past each
other horizontally is called a transform
boundary. At transform boundaries, the motion
of the two plates often produces earthquakes.
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Unit 4 Lesson 6 Plate Tectonics
Hot Plates
What causes tectonic plates to move?
• Scientists have proposed three mechanisms to
explain how tectonic plates move over Earth’s
surface.
• Some evidence suggests that convection, or the
movement of material due to differences in
density, in the mantle drags the overlying tectonic
plates along with it.
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Unit 4 Lesson 6 Plate Tectonics
What causes tectonic plates to move?
• The mechanism called ridge push suggests that as
lithosphere sinks, the plates are pushed away
from the mid-ocean ridge.
• The crust along the mid-ocean ridge is less dense.
As it cools, it becomes denser and sinks into the
mantle, pulling it away from the ridge.
• The force of the asthenosphere below pushes the
rest of the plate away from the mid-ocean ridge.
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Unit 4 Lesson 6 Plate Tectonics
What causes tectonic plates to move?
• The mechanism called slab pull suggests that
plates move because sinking plates pull them.
• The leading edge of a sinking plate is colder and
denser than the mantle, so it sinks. The rest of
the plate follows.
• Many scientists think slab pull is the most
important mechanism driving plate motion.
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