Name ____________________
Date ___________ Per ______
Plate Tectonics Part A- Theory of Plate Tectonics
Old 7th Grade Text Chap 14:3
Continental Drift Hypothesis
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In 1912 _______________________ suggested that all the continents were
once connected as one large landmass now called _________________
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Pangaea means “_______________________”
The land mass broke apart about _______________________ years ago and
The _______________________ slowly drifted to their present positions
Seafloor Spreading-explains the _________________ of the continents
• Hot dense material below the Earth’s ________________ rises upward to the
surface at the mid-ocean ridges
• Then it flows sideways, carrying the ____________________way from the ridge.
• As the new seafloor spreads apart, _________________ moves up and flows
from the cracks, cools, and forms new seafloor.
• _____________________ rocks are located at the mid-ocean ridges and become
increasingly older the further out you go.
Plate Tectonics
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In the 1960’s scientists developed a new theory that ___________________
continental drift and seafloor spreading.
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It is called ______________________________
Plate Tectonics
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The Earth’s ______________________ and upper mantle are broken into
sections.
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The sections, called _________________, move on a plastic-like layer of the
mantle
– Geologists use the term _________________ to describe the consistency of
rock that flows but is not a liquid like Silly Putty, modeling clay, or toothpaste.
Plate Tectonics
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The plates and upper mantle form the ______________________.
– The lithosphere is about ___________________ thick and generally is less
dense than the material underneath.
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The plastic-like layer is called the ____________________________
– The rigid plates of the lithosphere float and move around on the asthenosphere
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When plates move, they can interact in several ways.
– They can collide into each other, or pull apart, or slide alongside each other
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When plates interact, the result of their movement can be seen at the __________
___________________
Plates moving ___________________- Divergent Boundaries
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Plates moving apart at the __________________________ are examples of
divergent plate boundaries
– In the _______________________ Ocean, the North American Plate is
moving away from the Eurasian and the African plates.
– The ____________________________ in eastern Africa may become a
divergent boundary. The continental plate is being pulled
__________________.
Plates moving ____________________- Convergent boundaries
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As new crust is added in one place, it _________________ below the surface at
another.
Plates moving together- convergent boundaries
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When Ocean and Land Plates meet:
– The denser oceanic plates sink under less _____________ continental plates
– The area where the ocean plate moves down is called a __________________
– This type of convergent boundary forms a _________________________
Plates moving together- convergent boundaries
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When Ocean and Land Plates meet (continued):
– Newly formed hot _______________ is forced upward along the subduction
zones and forms volcanic mountains
– The ______________ Mountain Range in South America contains many
volcanoes that were formed at the ______________________ boundary of
the Nazca and South American plates
Plates moving together- convergent boundaries
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When Two Oceanic Plates Collide
– The older, denser plate will _______________ and sink down into the mantle.
– The __________________________ in the Western Pacific are a chain of
volcanic islands formed from two oceanic plates ____________________.
Plates moving together- convergent boundaries
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When Two Continental (Land) Plates Collide
– There is usually ______________________ because both of these plates
are less dense than the material of the __________________________.
– Plates will crumple up to form __________________________ ranges.
– __________________________ are common here, but not volcanoes.
– The ___________________________ in Asia are forming where the IndoAustralian plate collides with the Eurasian Plate
Plates Sliding Past each other- ______________________ Boundary
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When one plate slips past another suddenly _______________________ occur
– The Pacific Plate is ______________ past the North American Plate forming
the famous ____________________________________ in California.
Causes of Plate Tectonics
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____________________________ inside the Earth
– Cycle of heating, rising, cooling and sinking is called convection current.
– This process occurring inside the ______________________ of the earth is
the driving force behind ____________________________.
Features caused by Plate Tectonics
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The interaction of plates produces forces that build ___________________,
create _____________________________, and cause _________________.
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When rocks in the Earth’s crust break and move the energy is released as
_____________ waves
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We feel this release as ________________________________
Features caused by Plate Tectonics
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________________________, Faults and _____________________ Valleys
– are formed at divergent boundaries where plates are pulled apart.
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Mountains and ___________________ – are formed at convergent boundaries
where plates collide.
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Strike-Slip faults- cause of ________________________________ are found
at transform boundaries where plates grind past each other.
Testing for Plate Tectonics
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Using lasers and satellites, scientists can measure _________________ as little
as 1 cm per year.
– _______________ is moving toward Japan at a rate of about 8.3 cm per year.
– Maryland is moving away from _______________________ at a rate of 1.7
cm per year
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Scientists have observed that the plates move at rates from about _________ to
_________ per year.
Section Assessment- use a separate sheet, answer the following questions.
1. What happens to plates at a transform boundary?
2. What occurs at plate boundaries that are associated with seafloor spreading?
3. Describe the three types of plate boundaries where volcanic eruptions can
occur.
4. How are convection currents related to plate tectonics?
5. Using a flow map- describe the three theories that were discussed at the
beginning of the section.