Download MS Science - Kawameeh Middle School

Chapter Introduction
Lesson 1 Plate Tectonics
Lesson 2 Earthquakes
and Volcanoes
Lesson 3 Weathering,
Erosion, and
Deposition
Chapter Wrap-Up
Do you agree or disagree?
1.
Continents do not move.
2.
Earth’s mantle is liquid.
3.
Earthquakes occur and volcanoes erupt only
near plate boundaries.
4.
Volcanoes erupt melted rock.
5.
Rocks cannot change.
6.
Sediment can be transported by water, wind,
and ice.
Plate Tectonics
• What is the theory of plate tectonics?
• What evidence do scientists use to
support the theory of plate tectonics?
• How do the forces created by plate
motion change Earth’s surface?
Plate Tectonics
• plate tectonics
• transform
boundary
• continental drift
• subduction
zone
• convergent
boundary
• compression
• tension
• divergent
boundary
• shear
Plate Motion
• The theory of plate
tectonics states that
Earth’s crust is broken
into rigid plates that move
slowly over
Earth’s surface.
• The rigid plates are
called tectonic plates.
• North America is part of
the North American Plate.
Plate Motion (cont.)
• The movement of one plate is described
as either moving away from or toward
another plate, or sliding past another
plate.
• Plates move at speeds of only a few
centimeters per year.
• At this rate, it takes moving plates
millions of years to make new continents,
new mountain ranges, or other
landforms.
Plate Motion (cont.)
Long before
geologists proposed
the theory of plate
tectonics, they
discovered evidence
of continental
movement.
Photo by G.K. Gilbert, U.S. Geological Survey
Plate Motion (cont.)
• In 1912, Alfred
Wegener developed
the hypothesis that
continents move,
called continental
drift.
Plate Motion (cont.)
• One piece of
evidence is the
shape of Earth’s
continents.
• The outlines of South
America and Africa
match up like pieces of
a puzzle.
• Wegener used different types evidence to
back up his hypothesis:
– Geological evidence
– Fossil evidence
Plate Motion (cont.)
•Fossil and rock evidence
from the Gondwana
continents also supports
the hypothesis of
continental drift.
Geologists have discovered the same types
of fossils on continents that are now
separated by vast oceans.
Plate Motion (cont.)
•Scientists have also
found geological
evidence.
•Rocks that are made of
similar substances and
mountains that formed at
similar times are present
on continents that are now
far apart.
Plate Motion (cont.)
•Wegener’s hypothesis of
continental drift was not
accepted for more than 50
years after it was
proposed.
•The main reason for this
was because he could not
explain how the
continents could move.
Plate Motion (cont.)
• Convection is the circulation of particles
within a material caused by differences in
thermal energy and density
• Convection affects the mantle underneath
tectonic plates.
• Hotter mantle rises
toward Earth’s
surface and cooler
mantle sinks
deeper into the
mantle.
Plate Motion (cont.)
As the Earth’s mantle moves, it pushes
and pulls tectonic plates over Earth’s
surface.
Tectonic Plate Boundaries
• The edges of tectonic plates are called
plate boundaries.
• A convergent boundary is where two
plates move toward each other.
• A divergent boundary is where two
plates move apart from each other.
• A transform boundary is where plates
slide horizontally past each other.
Convergent Boundaries
• When two plates come together, the denser
oceanic plate usually is forced down into
the mantle and the less dense
continental plate remains
on Earth’s surface.
• The area where
one plate slides
under another
is called a
subduction zone.
Convergent Boundaries
• When two continents collide at a plate
boundary, both continents remain on the
surface.
• As two continents
push together,
the crust rises
up and large
mountains form.
Divergent Boundaries
• When plates move apart at divergent
boundaries, a rift forms between the two
plates.
• A rift can form within continents when
continental crust
moves in
opposite
directions.
Divergent Boundaries
• A rift also can form at divergent
boundaries on the ocean floor.
• As plates separate,
molten rock can
erupt from the rift.
• As the molten rock
cools, it forms new
crust.
Transform Boundaries
• Tectonic plates slide past each other at
transform boundaries.
• The two sides of the
boundary move in
opposite directions.
• This can deform or
break features such
as fences, railways,
or roads that cross
the boundary.
Forces Changing Earth’s Surface
• Forces within Earth cause plates to
move.
• The three types of plate boundaries
experience different types of forces.
• The squeezing force at a convergent
boundary is called compression.
• The pulling force at a divergent boundary
is called tension.
• The side-by-side
dragging force at
transform
boundaries
is called
shear.
Forces Changing Earth’s Surface (cont.)
• Even though plates move slowly, the
forces at plate boundaries are strong
enough to form huge mountains and
powerful earthquakes.
• Tensional forces pull the land apart and
form rift valleys and mid-ocean ridges.
• Compressional forces form mountains.
• Evidence of continental drift includes
fossils, mountain ranges, rock types,
and the shapes of continents.
• Earth’s crust is broken into pieces
called tectonic plates. Convection
currents in the mantle
cause the plates
to move.
• There are three types of tectonic plate
boundaries. Movement occurs at all
three boundaries.
Which boundary is between two
plates moving toward each other?
A. convergent
B. divergent
C. subduction
D. transform
Which zone describes the
boundary where one plate slides
under another plate?
A. convergent
B. divergent
C. subduction
D. transform
Which is the side-by-side
dragging force at transform
boundaries?
A. shear
B. tension
C. compression
D. continental drift
Do you agree or disagree?
1. Continents do not move.
2. Earth’s mantle is liquid.