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The Theory of Plate Tectonics
The Theory of Plate Tectonics
Pieces of Earth’s lithosphere (plates) are in
constant, slow motion, driven by
convection currents in the mantle.
The Theory of Plate Tectonics
Combines what geologists knew about
sea-floor spreading, Earth’s plates, and
continental drift into a single theory.
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Key Points
•The lithosphere is broken into separate
sections called plates.
Key Points
The plates float on top of the asthenosphere.
CRUST
Rigid Mantle
Key Points
•Movement of convection currents cause
plates to move.
Read, “How Plates Move” on
page 159
The Mosh Pit we call Earth’s Surface
•No plate can budge without affecting the other plates
surrounding it.
•As the plates move, they collide, pull apart, or grind past
each other.
•Causes changes in Earth’s surface (volcanoes, mountain
ranges, deep-sea trenches)
Speaking of Mosh Pit Analogies…
You can think of plate movements like
crowd surfing.
•where are the convection currents…and
where is the lithospheric plate?
Plate Boundaries
•Are where the edges of different plates meet.
•3 Types of plate boundaries:
Sliding Boundaries
• Where two plates slip
past each other, moving
in opposite directions.
• Produces: earthquakes
• Example – The San
Andreas Fault
Read, “Sliding boundary” on
page 161
Spreading Boundaries
•Where two plates
move apart.
•Produces: eruptions
of molten material,
new crust + earthquakes
•Examples – midocean ridge & the
Great Rift Valley in
East Africa
Read, “Spreading Boundary” on
page 160
Colliding Boundaries
•Where two plates
come together.
•Produces: volcanoes
or mountain ranges, +
earthquakes
•Examples –
Himalayas (India) &
Aleutian Islands
(Alaska)
Colliding Boundaries
•Density determines which
plate will come out on top.
Read, “Colliding Boundary” on
page 161
Tree Map
Plate
Boundaries
Write Type of
boundary
Write
definition
Draw a picture
& write