Download Which of these describes the lithosphere and the

Which of these describes the lithosphere and the
asthenosphere?
A.  The lithosphere is rigid and immovable, and the
asthenosphere is hot and flowing.
B.  The asthenosphere is rigid and immovable, and the
lithosphere is hot and flowing.
C.  Both are hot inner layers of earth capable of bending
and moving.
D.  Both are hard and rigid layers of earth close to the
surface.
Science Starter
9.4-5.13
The Plate Tectonic Theory
Tectonic Plates
Plates are large sections of the earth’s crust and
upper mantle that ride on top of the asthenosphere.
Plate Tectonics
•  In 1912, German scientist Alfred Wegener
proposed two ideas that are known as
continental drift Theory
–  Earth’s continents were once joined in a
single large landmass called Pangaea that
broke apart millions of years ago.
–  Continents have drifted to their current
location.
Continental Drift
•  It has taken the continents about 225 million
years since the breakup of Pangaea to move to
their present locations.
Pangaea
What do you notice about the movement
of the continent Pangaea to present day
continents?
The Moving Continents…
Plate Tectonics Explains
Continental Drift
Theory of Plate Tectonics
•  Claims that Earth’s plates are always in
motion
–  Plates move
•  slowly
•  at different rates
•  in different directions
–  Explains the formation,
movement, and
subduction of Earth’s
plates
Theory of Plate Tectonics
•  Crust rides on top of the plates
•  Plates ride on top of mantle which is in motion
due to convection currents
–  Convection currents can cause plates to move
away from each other or toward each other.
Two Types of Lithospheric Plates
•  Continental crust: made of rocks that are
less dense and ride higher on the mantle
than oceanic crust
–  Made of granite rock
•  Oceanic crust: rocks that are more dense
and ride lower on the mantle than
continental crust
–  Made of basalt rock
Plate Boundaries
•  Movement of Earth’s plates are responsible
for most major geological events and
landforms.
–  Volcanoes, earthquakes, mountain formation
•  Plate boundaries are where edges of plates
interact.
Earth’s Major Plates
Convection Currents
Convection Currents
•  Heat from the core causes convection currents
in the mantle.
•  Heating and cooling of the fluid, changes in the
fluid’s density, and the force of gravity combine
to set convection currents in motion.
Convection Currents in the Mantle
animation