th
8
Grade
Science
Plate Tectonics
 Geologists are scientists who study the
forces that make and shape the planet Earth.
 Geologists study the Earth’s interior
through seismic waves.
Geologists discovered the Earth has three layersthe crust, the mantle, and the core.
The oceanic crust beneath the ocean consists
mostly of dense rock like basalt.
Continental crust consists of less dense rock like
granite.
The upper mantle and crust make up the
lithosphere.
The asthenosphere is a soft layer that can bend
like plastic.
 Heat is transferred in the mantle through radiation,
conduction, and convection.
 Radiation is the transfer of heat through empty
space.
 Conduction is heat transfer by direct contact of
particles of matter.
 Convection is heat transfer by the movement of
heated liquid.
 Alfred Wegener first proposed the theory of continental
drift.
 Continental drift is Wegener’s theory that all continents
had once been joined together in a single landmass and
have drifted apart since.
 Wegener named this supercontinent Pangaea.
 Wegener’s theory was rejected by scientists because he
could not explain what force pushes or pulls continents.
Fossils of tropical plants found
on an island in the Arctic Ocean
are evidence for the theory of
continental drift.
 The mid-ocean ridge is the longest chain of
mountains.
 Most of the mountains in the mid-ocean ridge lie
hidden under hundreds of meters of water.
 Hess proposed that the ocean floors move,
carrying the continents along with them. The
movement begins at the mid-ocean ridge.
 At the mid-ocean ridge, molten material rises from
the mantle and erupts.
The process that continually
adds new material to the ocean
floor is called sea-floor
spreading.
 The ocean floor plunges into deep underwater
canyons called deep-ocean trenches.
 Subduction takes place in deep-ocean trenches.
 Subduction is the process by which the ocean floor
sinks beneath a deep-ocean trench and back into
the mantle.
 The lithosphere is broken into separate
sections called plates.
 The geological theory that states that pieces
of Earth’s lithosphere are in constant, slow
motion, driven by convection currents in the
mantle is plate tectonics.
GLE: 5.2.B.c: Describe (draw and write) how
the movement of crustal plates can cause
earthquakes and volcanic eruptions that can
result in mountain building and trench formation.
Pangea is Evidence that plates move.
See:
•http://www.divediscover.whoi.edu/tectonics/pangea-animation.html
•http://www.geo.cornell.edu/hawaii/220/PRI/PRI_PT_contdrift.html#
Faults are breaks in the Earth’s crust
where rocks have slipped past each
other.
 There are three kinds of boundaries that
explain plate movement.
 Understanding Plate motions:
 Plate Tectonics II
 The place where two plates move apart or
diverge is called a divergent boundary.
 A transform boundary is a place where two
 When a divergent boundary develops on
land, two of Earth’s plates slide apart.
 A deep valley called a rift valley forms
along the divergent boundary.
 A convergent boundary is where two plates
come together, or converge. The result of
the plates hitting together is called a
collision.
Practice MAP question:
•
Describe (draw and write) how the movement of crustal plates can cause earthquakes
and volcanic eruptions that can result in mountain building and trench formation. Click
on the links to see what kind of picture you should draw.
– Divergent boundaries -- where new crust is
generated as the plates pull away from each other.
This is where tectonic plates move away form each
other. New curst is formed. Sea-floor spreading
occurs.
– Convergent boundaries -- where crust is destroyed
as one plate dives under another or pushes into one
another. Crust can be melted and pushed up.
– Transform boundaries -- where crust is neither
produced nor destroyed as the plates slide
horizontally past each other.