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Earth’s Structure
• Earth’s interior is
made mostly of rock
4 main layers:
1) Inner Core
2) outer core
3) mantle
4) crust
Inner core
• Solid- made of iron and nickel
• Pressure from the other layers make it
• Compared to the seed of a peach
Outer Core
• Liquid
• Made mostly of iron and nickel
• Compared to the pit that covers the seed
of a peach
• Largest layer
• Contains silicon, oxygen, magnesium, and
• Upper mantle is plastic-like
• Compared to the juicy part of a peach
Thinnest layer
2 types of crust- oceanic and continental
Oceanic crust is thin and dense
Oceanic crust is basaltic
Until the 1960’s, we only had earthquake data
that told us what oceanic crust was like
• Glomar Challenger- drilled for rock samples on
the ocean floor
Science & New Ideas
• Without evidence, new ideas are not
• 2 theories not accepted at first
1) Wegener’s ideas about continental drift
2) Alvarez and dinosaur extinction
Alfred Wegener
• Edges of some
continents look like
they would fit together
like a puzzle
Alfred Wegener
• Wegener thought that
all the continents
were once connected
in a landmass known
as Pangaea (“all
Alfred Wegener
• Wegener had no evidence, so his ideas
were not accepted at first
• Wegener believed the landmass broke
apart 200 million years ago
• Continental drift is the idea proposed by
Wegener that the continents have drifted
horizontally to their current locations,
Walter & Luis Alvarez
• Dinosaur extinction theory
• Believed that a large rocky object hit Earth,
throwing tons of dust into the atmosphere,
blocking out sunlight, leading to the death of the
• Meteorite impact or
asteroid collision theory
Continental Drift
Evidence for continental drift
Early Evidence
• Fossil and Climate Clues
• Rock Clues
• Seafloor Spreading
Fossil & Climate Clues
• Reptile that lived in
• Found in South America
& Africa
• Continents must have
been connected at one
time because
Mesosaurus could not
have survived in ocean
Fossil & Climate Evidence
• Fern fossil
• Found in South America,
Australia, India, &
• Plants of warm climates
can’t survive in cold
climates, so at one time
all places must have had
similar climates
Rock Clues
• Similar rock structures are found on
separate continents
• Appalachian Mountains and mountains of
Europe line up
• Mountains of South America and western
Africa line up
• If the continents had been together, then
the mountain would line up and they do
Seafloor Spreading
• Echo sounding devices used to map the
seafloor (SONAR)
• The ocean floor has mountains and
valleys just like continents
• Mid-ocean rides form underwater
mountain ranges
Seafloor Spreading
• Harry Hess proposed the idea of seafloor
• Seafloor spreading is the idea that hot,
less dense material in the mantle (magma)
is forced up to the surface at mid-ocean
Seafloor Spreading
Steps of seafloor spreading
• Magma is forced upward.
• It turns and flows sideways
• Carries seafloor away from mid-ocean ridge in
both directions
• As the seafloor moves away, new magma
comes out and forms new seafloor
• Seafloor cools and becomes more dense than
the asthenosphere
• Cool seafloor then sinks down forming a trench
Age Evidence
• Glomar Challenger drilled for ocean floor
• The youngest rocks are at mid-ocean
ridges and get older as you go away from
the mid-ocean ridge
Age Evidence
• No rocks on the ocean floor were older
than 160 million years old
• Continental rocks are approximately 4
billion years old
Magnetic Clues
• Earth’s magnetic field has reversed itself
in the past
• Oceanic rock is basaltic, so it contains iron
• Iron aligns itself with the magnetic pole
• Rocks on the ocean floor show magnetic
Plate Tectonics
Theory of Plate Tectonics
Plate Tectonics
Plate Boundaries
Causes of Plate Tectonics
What is Plate Tectonics
• The Earth’s crust and upper
mantle are broken into
sections called plates
• Plates move around on top of
the mantle like rafts
Plate Tectonics
• (1968) Theory of plate tectonics is a
combination of the ideas of continental
drift and seafloor spreading
• Theory of plate tectonics states the
earth’s crust and upper mantle are broken
into sections called plates; these plates
move around on the mantle
Plate Tectonics
Lithosphere is the crust and upper mantle
Asthenosphere is the plastic-like layer
below lithosphere
The plates of the lithosphere are less dense
than the asthenosphere
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”
What is the Asthenoshere?
• The plastic layer below the
lithosphere = asthenosphere
• The plates of the lithosphere
float on the asthenosphere
3 Ways plates interact
1. Move toward each other and collide
2. Pull apart (DIVERGENT)
3. Move past one another (TRANSFORM
Plate Movement
• Result of plate movement is seen at plate
• Movement along any boundary requires
adjustment at another boundary
• For example, when the Pacific Plate and
the North America Plate slide past one
another, there are earthquakes in
California and where the plate collides with
another plate volcanoes form in Alaska
Tectonic Activities
Tectonic Activities
1. Mountain building
2. Earthquakes
3. Volcanoes
2 Types of Plates
• Ocean plates - plates below
the oceans
• Continental plates - plates
below the continents
Plate Boundaries
Divergent Boundaries
• Boundary between two plates that are
moving apart or rifting
• Examples: Great Rift Valley & MidAtlantic Ridge
Features of Divergent
• Mid-ocean ridges
• rift valleys
• fissure volcanoes
Convergent Boundaries
• Boundaries between two
plates that are colliding
 
• When crust is added in one place, it
disappears in another.
Convergent boundaries
3 Types of Convergent boundaries
1. Oceanic crust collides with continental
2. Oceanic crust collides with oceanic crust
3. Continental crust collides with continental
Convergent Boundaries
• Ocean plate colliding with a less dense
continental plate
• Continental plate is less dense than
oceanic plate
• Oceanic plate sinks into mantle
underneath continental plate because it is
more dense
Convergent Boundaries
• Subduction zone forms where dense
oceanic plate goes down into upper
• Volcanoes form in subduction zones
Andes Mountains,
South America
Convergent Boundary
• Ocean plate colliding with another
ocean plate
• One ocean plate bends and goes
under the other
• Volcanic island arcs are created
above the subduction zone.
Aleutian Islands, Alaska
Convergent Boundary
• A continental plate colliding with another
continental plate
• Continental plates are less dense than the
mantle so the plates will not sink and form
a subduction zone
• Mountain building takes place
• Example: Himalayas
Transform Fault Boundaries
• Boundary between two plates that are
sliding past each other
• EARTHQUAKES occur along these
• Plates can move in opposite
directions or same at different rate
• San Andreas Fault is an example
San Andreas Fault, CA
Causes of Plate
Convection Currents
• Hot magma in the Earth
moves toward the surface,
cools, then sinks again.
• Creates convection currents
beneath the plates that cause
the plates to move.
activity happens
at all plate