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Questions...
• What is the theory of plate
tectonics?
• What is the lithosphere?
• What is the asthenosphere?
• What is the connection between
the two?
• What are the two types of plates?
The Earth Has 3 Major Layers
Core
Inner
Outer
Mantle
Crust (Mantle)
Asthenosphere
Lithosphere
Core Link click here for book
Layers
The Crust
• The temperatures of the crust is 1600
degrees Fahrenheit (870 degrees Celsius)
in the deepest parts of the crust.
• Composed mostly of oxygen, silicon, and
aluminum
• The seven continents and ocean plates
basically float across the mantle which is
composed of much hotter and denser
material.
What is the Lithosphere?
• The crust and part of the upper
mantle = lithosphere
–100 km thick
–Less dense than the material below
it so it “floats”
–Continental Crust – granite
–Oceanic Crust - Basalt
• The oceanic crust consists of a volcanic lava rock
called basalt. Basaltic rocks of the ocean plates are
much denser and heavier than the granite rock of the
continental plates.
• Because of this the continents ride on the denser
oceanic plates.
• The crust and the upper layer of the mantle together
make up a zone of rigid, brittle rock called the
Lithosphere.
• The layer below the rigid lithosphere is a zone of
asphalt-like consistency called the Asthenosphere.
• The asthenosphere is the part of the mantle that flows
and moves the plates of the Earth.
2 Types of Plates
• Ocean plates - plates below
the oceans
• Continental plates - plates
below the continents
What is Plate Tectonics?
• The theory that the Earth’s lithosphere is
divided into plates that move on top of the
asthenosphere.
• The Earth’s crust and upper mantle are broken into
sections called plates
• Plates move around on top of the mantle like rafts
• Plates move along smoothly but sometimes they
stick and build up pressure. The pressure builds
and the rock bends until it snaps. When this occurs
and Earthquake is the result!
Plate Tectonics
The Earth is divided into layers due to
differences in density. These differences
are caused by differences in composition,
temperature, and pressure.
Plate Tectonics
•Theory of Continental
Drift – continents drift
apart from one another
and have done so for
years.
The Theory of Continental
Drift
Continental Drift Theory
• Proposed by Alfred Wegener in 1912
• 250 million years ago, all of the continents
were combined into one super-continent
called “Pangea”
• The continents gradually drifted apart to
where they are today
Pangaea
• Pangaea was a
time when all land
masses on Earth
were once
together as “all
earth”
• Panthalassa was
the sea that
surrounded all the
land – “all sea”
• Pangaea Link
About 180 Million Years Ago
• Laurasia was the
northern part of
Pangea composed
of N. America and
Eurasia
• Gondwana was the
southern part of
Pangea composed
of the remaining
continents.
135 Million Years Ago
– About 135 million years
ago Laurasia was still
moving, and as it moved it
broke up into the
continents of North
America, Europe and Asia
(Eurasian plate).
– Gondwanaland also
continued to spread apart
and it broke up into the
continents of Africa,
Antarctica, Australia,
South America, and the
subcontinent of India.
– Arabia started to separate
from Africa as the Red
Sea opened up.
– The red arrows indicate the
direction of the continental
Evidence of Continental Drift
•
•
•
•
Shapes of continents fit like a puzzle
Matching fossils found on different continents
Matching rock formations in Africa and S. America
Glacier patterns
The Same Plant and animal Fossils
found on different coastlines.
Same rock patterns found in South
America, India, Africa, Antarctica
and Australia
Ancient Climates
• Tropical plant remains
(coal deposits) found
in Antarctica
• Glaciation in Africa,
South America, India,
and Australia during
the same time
Supporting Evidence
•
Many years later (1950’s-1960’s) new
evidence provided better support like:
1. Earthquake belts
2. Locations of volcanoes
3. Magnetic reversal showed in igneous
rocks on the ocean floor, Mid-Ocean
Ridge
Mid-Ocean Ridge
• Seafloor Spreading click here for link and then
show Magnetic Reversal after seafloor spreading.
• Iceland straddles the Mid-Atlantic Ridge, and
offers a natural laboratory for studying on land
the processes that occur along the submerged
parts of the Mid-Atlantic Ridge.
Splitting along the N.
American and
Eurasian Plates as
N. America moves
westward relative to
Eurasia.
Lava fountains (10 m high) spouting from eruptive fissures during the
October 1980 eruption of Krafla Volcano. (Photograph by Gudmundur E.
Sigvaldason, Nordic Volcanological Institute, Reykjavik, Iceland.)
Aerial view of the area around Thingvellir, Iceland, showing a fissure zone
(in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Right
of the fissure, the North American Plate is pulling westward away from the
Eurasian Plate (left of the fissure). Large building (near top) marks the site
of Lögberg, Iceland's first parliament, founded in the year A.D. 930.
(Photograph by Oddur Sigurdsson, National Energy Authority, Iceland.)
More Interesting Stuff!
• Developing the theory [This Dynamic
Earth, USGS]
• Also read magnetic striping and polar reversal, and seafloor
spreading.
Convection Currents – the reason
why plates move!
• Causes of Tectonic Movement click here for interactive link.
Types of Plate Boundaries: Convergent,
Divergent, Transform click here for interactive book.
Diverging Plates
• Diverging Plate
Boundary is
where the
seafloor spreads.
• Two plates
moving in
opposite
directions
Divergent Boundaries
• Boundary between two plates
that are moving apart or rifting

• RIFTING causes Seafloor
Spreading, Fissure Volcanoes,
Rift Valleys
Diverging Boundary
continent / continent
• Rifting happens as they pull apart
• Rift valleys and seas form
• Great African Rift, Red Sea, Baja California
Convergent Boundaries
• Boundaries between two plates
that are colliding
 
• There are 3 types
–Ocean/Ocean
–Continent/Continent
–Continent/Ocean
Converging Boundary - ocean/ocean
• Subduction – more dense plate slides under
the less dense plates
• Forms trenches and volcanic island arcs
• Aleutian Islands, Mariana Islands, Mariana
Trench (deepest)
Where does the Krakin Live?
• Most likely in the
Trenches!
• These are the
deepest parts of
the ocean floor
and are created by
subduction!
http://blindkat.hegewisch.net/pirates/Na
utical_Myths.html#djl
Converging- continent/ocean
• Subduction
• Forms trenches and
volcanic mtn. ranges
• Peru-Chile Trench
(longest), Andes
Mtns.
Peru-Chile Trench
Nazca Plate
South
American
Plate
Off the coast of South America along the Peru-Chile trench, the oceanic Nazca
Plate is pushing into and being subducted under the continental part of the South
American Plate. The South American Plate is being lifted up, creating the towering
Andes mountains. Strong, destructive earthquakes and the rapid uplift of
mountain ranges are common in this region. The Nazca Plate is sinking smoothly
and continuously into the trench, the deepest part of the subducting plate breaks
into smaller pieces that become locked in place for long periods of time before
suddenly moving to generate large earthquakes. Such earthquakes are often
accompanied by uplift of the land by as much as a few meters.
The convergence of the Nazca and South
American Plates has deformed and pushed up
limestone strata to form towering peaks of the
Andes, as seen here in the Pachapaqui mining
area in Peru. (Photograph by George Ericksen,
USGS.)
Holy Cow !!!
On June 9, 1994, a magnitude-8.3 earthquake
struck about 320 km northeast of La Paz, Bolivia,
at a depth of 636 km. This earthquake, within the
subduction zone between the Nazca Plate and the
South American Plate, was one of deepest and
largest subduction earthquakes recorded in South
America. Fortunately, even though this powerful
earthquake was felt as far away as Minnesota and
Toronto, Canada, it caused no major damage
because of its great depth
Converging- continent/continent
• Collision zones where
folding and thrust fault
mountains form
• Himalayan Mtn (tallest),
Appalachian Mtns
(oldest)
Convergence of Continent to Continent
The collision between the Indian and
Eurasian plates has pushed up the
Himalayas and the Tibetan Plateau.
Before and After
Cross sections showing the meeting of these two plates
before and after their collision. The reference points (small
squares) show the amount of uplift of an imaginary point in
the Earth's crust during this mountain-building process.
Wild Beast of the Himalayas
Transform Boundaries
• Boundary between two plates
that are sliding past each other
• EARTHQUAKES along faults
• Most are found under the
ocean floor.
Transform Boundary
• Zones between
two plates
sliding
horizontally
past one
another.
Transform Boundary
The Blanco, Mendocino,
Murray, and Molokai
fracture zones are some of
the many fracture zones
(transform faults) that scar
the ocean floor and offset
ridges.
The San Andreas is one of
the few transform faults
exposed on land. This fault
moves approx. 5 cm/yr.
San Andreas Fault, California
• Pacific plate moving NW with respect to the
North American plate
Good-bye California 
The San Andreas fault zone, which is about 1,300 km long and in
places tens of kilometers wide, slices through two thirds of the length
of California. Along it, the Pacific Plate has been grinding
horizontally past the North American Plate for 10 million years, at an
average rate of about 5 cm/yr.
Land on the west side of the fault zone (on the Pacific Plate) is
moving in a northwesterly direction relative to the land on the east
side of the fault zone (on the North American Plate).
Questions...
• What are the three types of
boundaries?
• What direction do plates move at
each boundary?
• Which boundaries have a
subduction zone…what occurs at
a subduction zone?
Questions...
• What causes plates to move?
• How is a convection current
formed?