Plate Tectonics Notes and Vocabulary
Plate Tectonics is a theory developed in the late ________, to explain how the outer layers of the Earth _______ & ________. The
theory has caused a revolution in the way we think about the Earth. Since the development of the theory, geologists have had to
reexamine almost every aspect of Geology. Plate tectonics has proven to be so useful that it can predict geologic events and explain
almost all aspects of what we see on the Earth.
Lithosphere:_________________________________________________________________________________________________
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Asthenosphere:______________________________________________________________________________________________
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Theory:_____________________________________________________________________________________________________
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Tectonic Theories
Tectonic theories attempt to explain why ___________, ___________, and __________ occur where they do, the ages of
deformational events, and the ages and shapes of continents and ocean basins.
Meterologist:________________________________________________________________________________________________
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_____________ Theory of Continental Drift
Alfred Wegner was a German ______________ in the early 1900s who studied ancient climates. Like most people, the
jigsaw puzzle appearance of the Atlantic continental margins caught his attention. He put together the evidence of ancient
glaciations and the distribution of ____________to formulate a theory that the continents have moved over the surface of the
Earth, sometimes forming large supercontinents and other times forming separate continental masses. He proposed that prior
to about 200 million years ago all of the continents formed one large land mass that he called Pangea.
The weakness of Wegner's theory, and the reason it was not readily accepted by geologists was that he proposed that the
continents slide over ocean floor. ______________ disagreed, stating the ocean floor did not have enough strength to hold
the continents and too much frictional resistance would be encountered.
Geophysicist:________________________________________________________________________________________________
_________________________________________________________________________________________________
Topography:________________________________________________________________________________________________
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Sea-Floor Spreading
During World War II, geologists employed by the military carried out studies of the sea floor. The purpose of these studies was to
understand the ______________ of the sea floor to find hiding places for both Allied and enemy submarines. The topographic studies
involved measuring the depth to the sea floor. These studies revealed the presence of two important topographic features of the ocean
floor:
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___________________ - long sinuous ridges that occupy the middle of the Atlantic Ocean and the eastern part of the Pacific
Ocean.
__________________ - deep trenches along the margins of continents, particularly surrounding the Pacific Ocean.
Another type of study involved towing a ___________________ (for measuring magnetic materials) behind ships to detect
submarines. The records from the magnetometers, however, revealed that there were magnetic anomalies on the sea floor, with
magnetic high areas running along the oceanic ridges, and ______________ ________________ of _______________ high and low
magnetism on either side of the oceanic ridges.
Paleomagnetism - the discovery of reversals of the Earth's magnetic field and the magnetic time scale.
Reversals of the Earth's Magnetic Field. Studying piles of lava flows on the continents geophysicists found that over short time scales
the Earth's magnetic field undergoes __________ reversals (The ___________magnetic pole becomes the ___________ magnetic
pole) By dating the rocks using _____________ _________________ techniques and correlating the reversals throughout the world
they were able to establish the magnetic time scale.
Read pages 277-278 in your text book. Look at the pictures below. Using complete sentences, what evidence can be used to
explain sea floor spreading? How have magnetic clues been used to support the theory.
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If new oceanic crust and ________________ is continually being created at the _____________ _____________, the oceans
should be _____________indefinitely, unless there was a mechanism to _____________ the oceanic lithosphere. The oceanic
____________ provided the answer: Oceanic lithosphere returns to the mantle by sliding downward at the oceanic trenches
(______________). Because oceanic lithosphere is cold and brittle, it fractures as it descends back into the mantle. As it
fractures it produces earthquakes that get progressively deeper.
Seafloor Spreading:
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Continental Drift:
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Plate Tectonics:
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Pangea:
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Gondwana:
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Laurasia:
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Plate Tectonics
By combining the ___________
__________________ theory with
________________ _____________ and
information on global seismicity, the new
theory of Plate Tectonics became a coherent
theory to explain crustal movements.
Plates are composed of lithosphere, about
___________ km thick, that "float" on the
ductile asthenosphere.
Ductile:________________________________________________________________________________________________
______________________________________________________________________________________________________
Types of Plate Boundaries
Using complete sentences explain each type of plate boundary next to its picture. Use chapter 10 sec.
3 of your text book to help you.
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Divergent Plate Boundaries
 Convergent Plate Boundaries
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Transform Plate Boundaries
Cause of Plate Tectonics
In paragraph format and using complete sentences explain what causes plate tectonics. Use page 285 in
your text book to help you.
Using complete sentences explain the types of plate boundaries in this picture. Also, discuss how this
picture has illustrated the cause of plate tectonics.