Transcript Ch 9 Earth Science PPTx

Plate Tectonics
Ag Earth Science – Chapter 9.1
continental drift
 A hypothesis that
originally proposed that
the continents had once
been joined to form a
single supercontinent
Pangaea
 The proposed
supercontinent that 200
million years ago began
to break apart and form
the present landmasses
An Idea Before Its Time
 German scientist names
Alfred Wegener proposed
the hypothesis of
continental drift.
 Continental Drift – the
continents had once been
joined to form a single
supercontinent
 Pangaea – The name of the
“supercontinent” meaning
all land.
Evidence for Continental Drift Hypothesis
 The continental puzzle –
continents fit together like a
puzzle
 Matching fossils – fossil evidence
for continental drift includes
several fossil organisms found on
different continents.
 Rock type and structures – rock
evidence for continental drift
exists in the form of several
mountain belts that end at one
coastline, only to reappear on a
landmass across the ocean.
 Ancient climates – ancient
climate evidence supported
continental drift
A New Theory Emerges
 During the years that
followed Wegener’s
hypothesis, major strides
in technology enabled
scientists to map the
ocean floor.
 Extensive data on
earthquakes and the
Earth’s magnetic field led
to a new theory known as
plate tectonics.
Ag Earth Science – Chapter 9.2
plate tectonics
 The theory that proposes
that the earth’s outer
shell consists of
individual plates that
interact in various ways
and thereby produce
earthquakes, volcanoes,
mountains and the crust
itself
plate
 One of numerous rigid
sections of the
lithosphere that moves as
a unit over the material
of the asthenosphere
divergent boundary
 A region where the rigid
plates are moving apart,
typified by the oceanic
ridges.
convergent boundary
 A boundary in which two
plates move together
transform fault boundary
 A boundary in which two
plates slide past each
other without creating or
destroying lithosphere
Earth’s Major Plates
 According to the plate
tectonic theory, the
uppermost mantle, along
with the overlying crust,
behaves as a strong, rigid
layer. This layer is known
as the lithosphere.
 The lithosphere is
divided into plates.
Types of Plate Boundaries
 The three main types of
boundaries are
convergent, divergent,
and transform fault
boundaries.
 Divergent Boundaries –
two plates move APART
Types of Plate Boundaries
 The three main types of
boundaries are
convergent, divergent,
and transform fault
boundaries.
 Convergent Boundaries –
two plates move
TOGETHER
Types of Plate Boundaries
 The three main types of
boundaries are
convergent, divergent,
and transform fault
boundaries.
 Transform Fault
Boundaries – two plates
grind past each other
side-by-side
Ag Earth Science – Chapter 9.3
oceanic ridge
 A continuous elevated
zone on the floor of all
major ocean basins and
varying in width from
600 miles to 2400 miles.
The crests of ridges
represent divergent plate
boundaries.
rift valley
 Deep faulted structure
found along the axes of
divergent plate
boundaries. Can be
found on seafloor or
land.
seafloor spreading
 The process by which
plate tectonics produces
new oceanic lithosphere
at ocean ridges
subduction zone
 A destructive plate
margin where oceanic
crust is being pushed
down into the mantle
beneath a second plate
trench
 A surface feature in the
seafloor produced by the
descending plate during
subduction
continental volcanic arc
 Mountains formed in
part by volcanic activity
caused by the subduction
of oceanic lithosphere
beneath a continent
volcanic island arc
 A chain of volcanic
islands generally located
a few hundred miles
from a trench where
subduction of one
oceanic slab beneath
another is occurring
Divergent Boundaries
 Most divergent boundaries
are located along the crests
of oceanic ridges.
 Along well-developed
divergent plate boundaries,
the seafloor is elevated,
forming the oceanic ridge.
 Deep faulted structures
called rift valleys are found
along the axes of some
segments.
Divergent Boundaries
 Seafloor spreading is the
process by which plate
tectonics produces new
oceanic lithosphere.
Divergent Boundaries
 Continental Rifts - When
spreading centers
develop within a
continent, the landmass
may split into two or
more smaller segments.
Convergent Boundaries
 As two plates slowly converge
(come together head on), the
leading edge of one plate is
bent downward, allowing it to
slide beneath the other.
 Destructive plate margins
where oceanic crust is being
pushed down into the mantle
are called SUBDUCTION
ZONES.
 A subduction zone occurs
when one oceanic plate is
forced down into the mantle
beneath a second plate.
Convergent Boundaries
 Oceanic – Continental
 When the leading edge of a
continental plate converges
with an oceanic plate, the
less dense continental plate
remains floating.
 Continental volcanic arc /
volcanic activity is caused
by the subduction of the
oceanic crust melting
below when it sinks into
the asthenosphere.
Convergent Boundaries
 Oceanic – Oceanic
 When two oceanic slabs
converge, one descends beneath
the other.
 This causes similar volcanic
activity to what occurs with
oceanic-continental boundary,
however the volcanoes form on
the ocean floor.
 The newly formed land
consisting of an arc shaped chain
of small volcanic islands is called
a volcanic island arc. (example –
Aleutian Islands near Alaska)
Convergent Boundaries
 Continental – Continental
 When an oceanic plate is
subducted beneath
continental lithosphere, a
continental volcanic arc is
created. However, if the
subducting plate also has
continental lithosphere,
the subduction eventually
brings the two continents
together and the collision
forms complex
mountains.
Transform Boundaries
 At a transform fault
boundary, plates grind
past each other without
destroying the
lithosphere.

Example – San Andreas
Fault