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Integrated Science One
Plate Tectonics
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Main Layers of Earth
• Crust
Lithosphere includes the crust and upper
mantle
• Mantle
• Core
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1. Crust
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This is the skin of the earth
Only between 8 and 67 kilometers thick
It is deepest beneath mountains
Oceanic crust is thinner and more dense
than continental crust
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Types of Crust
• Oceanic crust is dense and found beneath
the oceans and has a thickness of about
4-7km.
• Continental crust is thicker and less dense
and has an average thickness of
approximately 20-40 km.
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2. Mantle
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Beneath the crust
Heavier than the crust
Between 2800 and 3000 km thick
Seems to be in a fluid state
Makes up about 80% of the Earth’s
volume
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3. Core
• Beneath the mantle
• Made up of 2 parts
– Outer core which contains melted iron and
nickel
– Inner core which is hot and solid
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Differences in the 3 main layers
• Crust and mantle are both made of hard
solid rock, but the crust is less dense than
the mantle.
• The core is believed to be composed of
iron and nickel
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Alfred Wegener
• He proposed that based on physical
evidence from coastlines, rocks, and
fossils the continents were all connected
approximately 200 million years ago in a
supercontinent called Pangaea.
• This theory is called continental drift
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• One hypothesis states that plate
movement results from convection
currents in the asthenosphere
• Asthenosphere – the zone of the mantle
beneath the lithosphere that consists of
slowly flowing solid rock
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Plate Tectonics
• Theory stating that crustal plates on the
surface of Earth are continuously moving
due to convection currents.
– Types of movement of plates
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Divergent
Convergent
Subduction
Transform fault
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Occurances at boundaries of plates
• Earthquakes
• Volcanoes
• Mountain formation
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Divergent boundary
• Occurs where two plates move away from
each other
• Forms rift valleys in oceanic crust
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Convergent Boundary
• Where two plates move toward each other
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Transform fault
• Occurs where two plates move past each
other
• Breakage of rocks along a fault line
releases energy in the form of seismic
waves producing earthquakes
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Earthquakes
• Occur at transform faults
• Seismograph measures how much the
surface of Earth moves during an
earthquake
• Surface waves are the most damaging
• Minimum number of seismograph stations
needed to determine earthquake’s
epicenter is three
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More on Earthquakes
• The magnitude of earthquakes is
expressed using the Richter scale
• The Richter scale expresses the relative
magnitude of an earthquake, which is a
measure of the energy released at the
focus of an earthquake
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Subduction zone
• Zone where oceanic crust dives beneath
continental crust
• In subduction zones, when a denser plate
dives into the mantle, the rock reaches its
melting point and begins to melt and form
magma – hot, low density magma rises to
surface forming mountains and volcanoes
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Volcanoes
• A vent in Earth’s crust through which hot,
liquid rock come to the surface
• Magma released from volcanoes is molten
rock from the mantle and crust
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• Volcanoes are common around the edges
of the Pacific Ocean because as the
Pacific Plate is subducted under
surrounding plates, the Pacific Plate is
forced into the mantle, where the rock
melts and rises to the surface, creating
volcanoes
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Types of Volcanoes
• Shield – rich in magnesium and iron
• Cinder – caused by large amounts of gas
trapped in the magma
• Composite – composed of many layers of
cinders and lava
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Rock Types
• Igneous –
• Sedimentary –
• Metamorphic – changed by heat and
pressure. Sedimentary can change into
metamorphic
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Igneous
• Formed from magma cooling
• Those that have mineral crystals easily
seen with the unaided eye formed
intrusively (geode)
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Sedimentary
• Formed by weathering
• Named according to size of the fragments
they contain
• Can contain fossils
• Limestone (a sedimentary rock) can be
metamorphosed into marble
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Metamorphic
• Rocks that are changed by heat and
pressure will form this type of rock
– When heated, both igneous and sedimentary
rock become metamorphic
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Age of rocks
• Superposition is used to determine the
relative age of rocks
• Radioactive isotopes are used to
determine a more exact age of rocks
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New evidence supporting theory of
plate tectonics
• Bands of rock with alternating magnetic
polarities were discovered on either side of
the Mid-Atlantic Ridge in the 1960s. As the
youngest rock appears near the center of
the ridge and the oldest rock appears
further away, this suggests that the
oceanic plates are moving away from the
plate boundary
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Weathering of rocks
• Physical weathering does not alter the
chemical compositon of rock
• Water is the most effective agent of
physical weathering and erosion
• The process in which sediment is laid
down is called deposition
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Weathering
A. Physical - breaks rock into smaller
pieces
1. ice
2. plants
B. Chemical
1. carbon dioxide dissolved in
water can dissolve rock
2. acid rain can dissolve minerals
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Essay Questions – choose 1
• How does a seismograph work?
• The Himalayas are a mountain range in
India that continues to increase in both
width and height. Describe the type of
plate boundary found in this region and
explain the reason behind the formation of
the mountain range
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Erosion
II. Erosion - process by which rock and /or
the products of weathering are removed.
A. Water
B. Wind
C. Glaciers
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• How do seismograms recorded during
earthquakes help scientists learn about
the composition of Earth?
• In an earthquake-prone area, which earth
material – igneous rock or sedimentary
rock – would be better for constructing
buildings? Explain your answer.
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