Transcript Plate Tectonics

th
6
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.
Faults are breaks in the Earth’s crust
where rocks have slipped past each
other.
 The place where two plates move apart or
diverge is called a divergent boundary.
 A transform boundary is a place where two
plates slip past each other, moving in
opposite directions.
 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.