Plate Tectonics
Chapter 6
Section 6.1
Earth is made up of materials with
different densities
• Crust
• Mantle
• Core
Earth’s layers have different
properties
To explore the interior, scientist study the
energy form earthquakes or underground
explosions they set off.
1. Core, Mantle, Crust
2. Lithosphere and Asthenosphere
The Core
• The core is Earth’s
densest region and is
made up of two parts:
1. The inner core, is a ball
of hot, solid metals.
2. The outer core, is a
layer of liquid metals
that surrounds the inner
core.
Inner Core
* The inner core of the
Earth has
temperatures and
pressures so great
that the metals are
squeezed together
and are not able to
move.
* The inner core is a
solid.
Outer Core
* The core of the Earth
is like a ball of very
hot metals.
* The outer core is
liquid.
* The outer core is
made up of iron and
is very dense.
The Mantle
• The mantle is the
layer below the crust.
• The mantle is the
thickest layer of the
Earth.
• It has layers of cool,
rigid rock at the top
and a layer of hotter
softer rock below it.
The Crust
• Outer and thin layer
or cool rock.
• 2 types of crust
– Oceanic (all the ocean
floors)
– Continental (all the
continents, and major
islands)
Oceanic and Continental Crust
Earth’s crust is thinnest under the oceans and thickest under continental
mountain.
The crust is home for all life on earth
Earth’s Layers
• How are the earth’s
layers similar to an
egg?
• Shell=crust
• Egg white=mantle
• Yolk=core
In the Mantle
LITHOSPHERE
• The word litho- means
“stone” or “rock”.
• Earth’s crust and the very
top of the mantle.
• Is the most rigid of all
layers.
ASTHENOSPHERE
• The word asthenes
means “weak”.
• A layer of hotter softer
rock in the upper mantle.
• Solid rock that flows
slowly (like hot asphalt)
Tectonic Plates
• Earth’s crust is broken into about 19
pieces
• These plates move on top of the
asthenosphere
The thicker continental crust rises above ocean.
The rest of the plate is thin oceanic crust, or sea
floor.
Earth’s layers and Tectonic
Plates are the most important
discoveries in geology
They helped answer the questions:
1.Have the continents always been where
they are today?
2. If not, how did they move to their present
positions?
Continents change position over
time
• German scientist Alfred Wegner proposed
a hypothesis known as continental drift.
• He hypothesized that Earth’s continents
were once joined in a single landmass and
gradually moved or drifted apart.
Evidence for Continental Drift
1. Fossils of Mesosaurus have been
discovered in both South America and
Western Africa.
1. Climate. Fossils of tropical plants found in
icy Greenland, and rocks deeply
scratched by ice sheets that once
covered the area.
2. Geology, type of rock found in Brazil
matched the rock found in western Africa.
movie
Pangaea and Continental Drift
• What is Pangaea?
it is Wegner’s name for the supercontinent
that once reached from pole to pole.
• Pangaea began to split apart some 250
million years ago.
• Wegner needed more explanation.
Evidence from the Sea Floor
• Mid-ocean ridges are huge underwater
mountain ranges.
www.divediscover.whoi.edu/ridge/axial.html
Sea-floor spreading
• The ridges form along cracks in the crust.
Molten rocks rise, cool and form new
oceanic crust. The old one is pulled away
to make room for new material.
Age of the Sea Floor
• The rock samples obtained from the sea
floor revealed that the youngest rock is
closest to the ridge, and the oldest rock is
farthest away.
Ocean Trenches
Why does Earth remain the same size??
• In the sea floor trenches like deep
canyons are found.
• At ocean trenches, dense oceanic crust is
sinking into the asthenosphere.
• Old crust is being destroyed at the same
rate that new crust is forming.
Scientists now had proof that
tectonic plates move
• Tectonic plates are the lithosphere layer
broken into small and large slabs of rocks.
• Tectonic plates rests on the
asthenosphere, rocks in this layer moves
by convection.
• Convection is energy transfer by the
movement of a material.
• Convection currents are the motions that
transfer heat energy in a material.
Causes of Plate Movements
• Convection currents, slab pull, and ridge
push move Earth’s huge tectonic plates.
Causes of Plate Movement
• In the asthenosphere, heated rock
constantly rise, cools, sinks and is heated
again. This is convection currents.
• Slab pull occurs when gravity pulls cooler,
denser rock into the asthenosphere.
• Ridge Push occurs when material from
mid ocean ridges push the plates.
Putting things together
• Geologists combined their knowledge of
Earth’s plates, the sea floor and the
asthenosphere to develop the theory of
plate tectonics.
What does the theory of plate
tectonics state?
• Earth’s lithosphere is made up of huge,
moving plates that are carried over Earth’s
surface.
• Most earthquakes, volcanoes and
mountain ranges appear where tectonic
plates meet.
Plates move apart
Section 3
Tectonic plates have different
boundaries
• A plate boundary is where the edge of two
plates meet.
• There are 3 boundaries
A. divergent boundary
B. convergent boundary
C. transfrom boundary
• Divergent boundary occurs where plates
move apart.
• Found mostly in the ocean.
• Convergent boundary occurs where plate
push together.
• Transform boundary occurs where plates
scrape past each other.
Mid Ocean Ridges and Rift
Valleys
• As the sea floor spreads, it creates a gap
between the ridges called Rift Valley.
• Mid- ocean ridges, rift valleys form along
divergent boundary, as the sea floor
spreads apart.
The boundary overview movie
Sea-Floor Rock and Magnetic
Reversals
• Patterns of Magnetic Reversal recorded in
ocean- floor rocks provide evidence of
plate movement.
• Magnetic reversal is when the north pole
becomes south and the south pole
becomes north.
Continents splits apart at
divergent boundaries
• On land the hot material rises in the
mantle causes the curst to bulge upward,
then it cracks. As rift valley widen,
continents begin to split apart.
• If the rift valley continued to widen, the
thinned valley floor sinks lower and lower
until it is below sea level.
• The valley will
be flooded by
nearby oceans
or rivers forming a
a sea or a lake.
Hot spots can be used to track
plate movements
• A plume of magma from the mantle melts
the rock in the plate above it until a
volcano forms.
• They provide a fixed point to measure
plate movements.
Plates converge or scrape
past each other
Ch 6, section 4
Tectonic plates push together at
convergent boundaries.
• At convergent boundaries, crust is either
folded or destroyed.
• When one plate sinks beneath another is
called subduction.
There are 3 types of convergent
boundaries
1. Two continental plates meet
2. Two oceanic plates meet
3. An oceanic plate and a continental plate
meet.
Continental-Continental
Collision
• Occurs where two plates carrying
continental crust push together.
• Neither plates can sink under the other
because they have the same density.
• The edges will crumple and fold when they
collide.
• The folded crust can be pushed up high to
form mountains.
• The Alps are forming as a result of the
European and African plates pushing
together.
European Alps
The Himalayas
Subduction
When one plate sinks beneath another is
called subduction.
1. Oceanic-Oceanic Subduction
2. Oceanic-Continental Subduction.
Oceanic-Oceanic Subduction
• Occurs where one plate with oceanic crust
sinks, or subducts under another plate of
oceanic crust.
• The older plate sinks because it is denser
than the younger plate.
• When the older crust reaches the
asthenosphere it melts in the intense heat.
Two main features from
oceanic-oceanic subduction
1. Deep ocean trenches.
1. Island arcs.
1. Deep ocean trenches
They are deep canyons that form in the
ocean floor as the plate sinks.
2. Island arcs
They are volcanic island forms in parallel to
a deep ocean trenches.
Oceanic-Continental Subduction
• Occur when ocean crust sinks under
continental crust.
• The oceanic crust sinks because it is older
and denser than the continental crust.
Two main features form
oceanic- continental subduction
1.Deep ocean trenches
it forms as the oceanic plate sinks.
1.Costal mountains (volcanic islands)
magma rises through the cracks in the crust
and forming volcanoes on the surface
Tectonic plates scrape past
each other at transform
boundaries
• At transform boundaries, crust neither
formed nor destroyed.
• As the plates move
their edges scrape
and grind against
each other
• Transform boundaries occur mostly on
1.The sea floor near mid-ocean ridges
2.On land seen as long cracks in Earth’s
surface.
San Andreas Fault
The theory of plate tectonics
helps geologists today
• Scientists learned
1. The planet’s lithosphere has been moving
for millions of years.
2. Earth’s past and it helped them predict
Earth’s future as well as the sites or future
volcanoes, earthquakes, mountain
building.
Open Your Book Pg 216
Do question 19, 20, and 22