Transcript Link here - 8 SCIENCE RED

Plate Tectonics Ch 4
Earth’s Interior Section 1
Layers of the Earth Section 2
Drifting Continents Section 3
Plate Boundaries Section 4
The Theory of Plate Tectonics Section 5
Section 1:
Earth’s Interior
• We know about the earth’s interior from
indirect evidence
– Example of indirect evidence: How would you
know where to hang a picture so that it stays hung
solidly? You can’t see inside the wall.
• Temperature and pressure change as you
go deeper towards the core
– Temperature increases towards the center of the
earth
– Pressure also increases towards the center
Cross-section of earth’s interior showing
crust, mantle and the two parts of the core
Four Main Layers of the
Earth’s Interior
• The crust – the layer of rock that forms
the earth’s outer skin, includes rocks,
mountains, soil and water
• The mantle – 5-40 km down. Rock is of
hotter temperatures. About 3,000 km thick
• The outer core – liquid molten iron metal
• inner core – solid iron metal due to high
pressure
This slide shows how temperature increases
towards the center of the earth, as well as some
of the elements found in each layer.
Seismic waves are a
window to the interior of
the earth. S-waves
do not travel through
liquids. A shadow
zone occurs on the
opposite side of
the earth from
where the earthquake occurred.
All seismic
stations in the
shadow zone
would record
P-wavesbut not
S-waves.
Earth’s Magnetic Field
Currents in the liquid outer core force
the solid inner core to spin at a slightly
faster rate than the rest of the planet.
These currents in the outer core create
the magnetic field causing the earth to
act like a giant bar magnet.
The magnetic field protects living things
from dangerous solar radiation.
Convection
Currents and the Mantle
Section 2:
• In the upper-most part of the Mantle is a rigid
layer called the lithosphere. Litho means rocky
or stone.
• Below the lithosphere is the asthenosphere,
which means weak, but it is actually semimolten and the semi-melted rock is moving in
slow currents!
• The lithosphere rides on top of the slow moving
asthensphere.
Convection
Convection is heat transfer by movement of
heated fluid (gas or liquid).
Heat transfer by convection is caused by
differences of temperature and density
within that fluid (for example, how this room is heated)
The heating and cooling of the fluid,
changes in the fluid’s density, and the
force of gravity all combine to set
convection going in the earth’s mantle.
This slide
shows the
convection
currents found
in the
asthenosphere.
(Note the
drawing is not
drawn to scale)
These convection cells move sections of the
crust. Hot, less dense molten lava rises to the
surface creating new crustal sections. Old
crust is “subducted” or forced down in the
earth, melting and recycling!
Section 3:
Drifting Continents
• 1910 Alfred Wegener hypothesized that all the
continents had once been joined together in a single
landmass and have since drifted apart.
• Evidence includes mountain ranges that line up,
fossils that were similar, mineral deposits that also
lined up, as well as climate evidence and traces
• Most scientists at the time did not believe in this
theory of drifting continents, as Wegener could not
explain what force was actually moving the
continents.
Section 4:
Sea-Floor Spreading
• Mapping the Mid-Ocean Ridge – the longest
chain of mountains in the world! (and they are underwater)
• Sonar
mapping
(begun in
1959)
revealed the
location of
these
Mountains
Evidence of Sea-Floor Spreading
• Ocean floors move
like conveyor belt,
carrying the continents
along with them.
• At the mid-ocean
ridge, molten material
rises from the mantle
and erupts. The
molten material then
spreads out, pushing
older rock to both
sides of the ridge.
This little animation shows molten lava coming to the
surface at the mid-oceanic ridge. As it reaches the
surface, the lava cools, hardens and is pushed aside
by new magma coming to the surface.
Sea-Floor Spreading
Review of Evidence
• Molten material
found erupting along
mid-ocean ridge
• Iron within basaltic
crust magnetized.
• Strips on either side
of the mid-ocean
ridge that match up
Subduction at Deep-Ocean Trenches
Trenches – forms
where the oceanic
crust is thrust back
down into the mantle
and begins cracking
and melting
Crust and Lithosphere
being thrust down at
subduction zones.
Notice the melting of
the plate, forming the
pockets of hot magma
Section 5:
The Theory of Plate Tectonics
• The Theory of Plate Tectonics explains the
formation, movement, and subduction of
Earth’s plates.
• There are three types of plate boundaries:
convergent, divergent, and transform.
• Plate converge in three different way: Two
ocean crusts colliding, two continental crusts
colliding, and a continental crust colliding with
an ocean crust.
Location of earthquakes and volcanoes found
along convergent and divergent plate boundaries
(and over hot spots such as Hawaii and Yellowstone)
Ring of Fire
Plates of the Earth
Plate Boundaries
Transform, Divergent, Convergent
Convergent Plate Boundaries
Two plates “coming together”
Ocean crust | Ocean crust (Japan, Taiwan)
Ocean crust | Continent crust (Andes Mts.)
Continent crust | Continent crust (Himalaya Mts.)
Folded Mountain Belts occur
when continents are involved
(similar to “rug” analogy)
Divergent Plate Boundaries
Two plates “moving apart”
Plates are created and move apart at the
mid-oceanic mountain range in the Atlantic
Ocean
Transform Faults
Two plates “slide” past each other.
San Andreas Fault in Southern California
San Andreas Fault in
California (transform fault)
Review of Terms
Locate: Trench, folded mountain belts, mid-oceanic
ridge, volcanoes, hot spots, crust, subduction zones,
transform fault, lithosphere, convergent plate
boundary, divergent plate boundary, asthenosphere
Motion
of
India’s
plate
The
formation of
a rift valley
Convergent Boundary
Can you identify and
describe each type
of convergent plate
boundary?
How islands are formed: Hot spots
in the crust allow melted magma to
form little cones on the ocean floor
that build higher and higher to
create islands.
Earthquakes
What is
happening to the
Red Sea?
Will we need to
someday rename
Lake Victoria to
Victoria Ocean?
Folded Mountain Belts