2. The theory that states that pieces
of Earth’s lithosphere are in
constant, slow motion, driven by
convection currents in the mantle.
3. • The theory of plate tectonics
explains the formation,
movement, and subduction of
Earth’s plates.
4. Forces that causes Earth’s
plates to move.
• The plates of the lithosphere float on top of the Asthenosphere.
• Convection currents rise in the Asthenosphere and spread out
beneath the lithosphere.
• Convection current forces drag the overlying plates along. The
currents cools and sinks deeper into the mantle.
• Scientist think that the downward movement may provide the
force that causes the subduction of plates carrying oceanic crust.
6. Slab Push Hypothesis
• Magma rising along the mid oceanic
ridge exerts a force that pushes an oceanic
plate away from the ridge.
• The force of gravity causes plate
movement by pulling cooler, denser
oceanic plates down toward the mantle.
• Slab push and pull work together with
convection currents to move the plates.
7. The earth’s surface is made
up of about nine large plates
& several smaller plates.
16. • When divergent boundary
develop on land, two of Earth’s
plates slide apart.
• A rift valley forms along the
divergent valley.
• Ex. The Great Rift Valley in
east Africa is about 3,000
kilometers long.
19. • When plates converge, it
results in a collision.
• Collisions happen between:
1. Oceanic crust to oceanic crust
2. Oceanic crust to continental crust
3. Continental crust to continental crust
23. Plate Movement
• The plates move at about 1-10
centimeters per year.
• The North American and Eurasian
plates move at about 2.5 cm/year.
24. Plate Movement
• Pangaea existed about 260 million
years ago.
• Approximately 225 million years ago
Pangaea began to break apart.