Download The Birth of a Theory

ESC 1000 Earth and Space Science Video Lecture Notes
Name: ________________
Earth Revealed #5 and #6: Birth of a Theory/Plate Dyanmics (1992)
Please watch the video in class. Take notes on the Earth Revealed Discs #5Birth of a Theory and #6: Plate Dyanmics.
Please circle each of the Chapter 7 vocabulary words discussed in the video. When the film is finished and after reading
Chapter 6 Grs, Deserts and Wind, write questions with answers that a student should be able to answer if she/he viewed
this video. You should have at least two or more questions for each chapter. List the most significant discovery you
made about Weathering and Soils which you did not know before watch the film.
Play Video: http://www.learner.org/resources/series78.html
Chapter 7: Plate Tectonics (Chapter 8 - 11th Edition)
Key Concepts
Ch. 7: Plate Tectonics
(Chapter 8 - 11th Edition)
After reading and studying Ch. 8, you should be able to:
Concept 1: Compare and contrast the scientific ideas and
definitions for the continental drift hypothesis and the
theory of plate tectonics.
Concept 2: Explain the differences among divergent,
convergent, and transform plate boundaries, including the
major processes that occur at these boundaries.
Concept 3: List and describe the evidence used to support the Plate Tectonics
theory.
Concept 4: Describe the models that have been proposed to explain the driving
mechanisms for plate motion.
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Chapter Summary
Summary
The following statements summarize and describe many of the key terms and concepts
presented in the chapter.
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In the early 1900s Alfred Wegener set forth his continental drift hypothesis. One
of its major tenets was that a supercontinent called Pangaea began breaking apart into
smaller continents about 200 million years ago. The smaller continental fragments
then "drifted" to their present positions. To support the claim that the now-separate
continents were once joined, Wegener and others used the fit of South America and
Africa, the distribution of ancient climates, fossil evidence, and rock
structures.
One of the main objections to the continental drift hypothesis was the inability of its
supporters to provide an acceptable mechanism for the movement of continents.
The theory of plate tectonics, a far more encompassing theory than continental drift,
holds that Earth's rigid outer shell, called the lithosphere, consists of seven large and
numerous smaller segments called plates that are in motion relative to each other.
Most of Earth's seismic activity, volcanism, and mountain building occur along
the dynamic margins of these plates.
A major departure of the plate tectonics theory from the continental drift hypothesis is
that large plates contain both continental and ocean crust and the entire plate moves.
By contrast, in continental drift, Wegener proposed that the sturdier continents
"drifted" by breaking through the oceanic crust, much like ice breakers cut through
ice.
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Divergent plate boundaries occur where plates move apart, resulting in upwelling
of material from the mantle to create new seafloor. Most divergent boundaries occur
along the axis of the oceanic ridge system and are associated with seafloor spreading,
which occurs at rates between about 2 and 15 centimeters per year. New divergent
boundaries may form within a continent (for example, the East African rift valleys),
where they may fragment a landmass and develop a new ocean basin.
Convergent plate boundaries occur where plates move together, resulting in the
subduction of oceanic lithosphere into the mantle along a deep oceanic trench.
Convergence between an oceanic and continental block results in subduction of the
oceanic slab and the formation of a continental volcanic arc such as the Andes of
South America. Oceanic-oceanic convergence results in an arc-shaped chain of
volcanic islands called a volcanic island arc. When two plates carrying continental
crust converge, both plates are too buoyant to be subducted. The result is a "collision"
resulting in the formation of a mountain belt such as the Himalayas.
Transform fault boundaries occur where plates grind past each other without the
production or destruction of lithosphere. Most transform faults join two segments of an
oceanic ridge. Others connect spreading centers to subduction zones and thus
facilitate the transport of oceanic crust created at a ridge crest to its site of
destruction, at a deep-ocean trench. Still others, like the San Andreas Fault, cut
through continental crust.
The theory of plate tectonics is supported by (1) paleomagnetism, the direction and
intensity of Earth's magnetism in the geologic past; (2) the global distribution of
earthquakes and their close association with plate boundaries; (3) the ages of
sediments from the floors of the deep-ocean basins; and (4) the existence of island
groups that formed over hot spots and that provide a frame of reference for tracing
the direction of plate motion.
Three basic models for mantle convection are currently being evaluated. Mechanisms
that contribute to this convective flow are slab-pull, ridge-push, and mantle plumes.
Slab-pull occurs where cold, dense oceanic lithosphere is subducted and pulls the
trailing lithosphere along. Ridge-push results when gravity sets the elevated slabs
astride oceanic ridges in motion. Hot, buoyant mantle plumes are considered the
upward flowing arms of mantle convection. One model suggests that mantle
convection occurs in two layers separated at a depth of 660 kilometers. Another model
proposes whole-mantle convection that stirs the entire 2900-kilometer-thick rocky
mantle. Yet another model suggests that the bottom third of the mantle gradually
bulges upward in some areas and sinks in others without appreciable mixing.
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Earth Revealed #5. The Birth of a Theory
In the 1960s, earth scientists developed the theory of plate tectonics. This program traces the development
of plate tectonics, beginning with the contributions and methods of geologist Alfred Wegener. Sea-floor
spreading, continental drift, paleomagnetism, and the primordial supercontinent Pangaea are some of the
topics covered.
Play Video: http://www.learner.org/resources/series78.html
Video Notes:
Chapter 7: Plate Tectonics: A Scientific Theory Unfolds
Asthenosphere
Island arc
Plate tectonics
Continental drift theory
Lithosphere
Reverse polarity
Continental volcanic arc
Magnetic time
scale
Ridge push
Convergent plate
boundary
Mantle plume
Rift (rift valley)
Curie Point
Normal polarity
Seafloor is spreading
Deep-ocean trench
Ocean ridge
system
Slab pull
Divergent plate boundary
Paleomagnetism
slab suction
fossil magnetism
Pangaea
Subduction zone
Fracture
Partial melting
Transform fault
boundary
Hot spot
Plate
Volcanic island arc
Student Questions (with Answers):
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2.
3.
Most Significant Discovery (discoveries):
Video Study Guide: Earth Revealed
Episode 5: The Birth of a Theory
What unifying theory united diverse geological phenomena?
List some of the evidence for Continental Drift.
Who was Alfred Wegener?
What was his "torn newspaper" analogy?
What did skeptics attack about his theory?
What mechanism did he propose for Continental Drift?
What technology developed during WW II helped the theory?
What is "Seafloor Spreading?"
What are "Subduction Trenches?"
How is "Paleomagnetism" used to support seafloor spreading?
How did a study of "Magnetic Field Reversals" support seafloor spreading?
What are "Transform Faults?"
How did drilling by the Glomar Challenger support seafloor spreading?
What is "Convection" and how does it relate to Plate Tectonics?
Earth Revealed #6. Plate Dynamics
This program examines the movement and interaction of tectonic plates, which account for a vast array of
geologic formations and phenomena — from California’s San Andreas Fault to the Rift Valley of eastern
Africa. The program covers convergent boundaries, subduction, hotspots, and the debate over what drives
plate motion.
Play Video: http://www.learner.org/resources/series78.html
Video Notes:
Student Questions (with Answers):
1.
2.
Most Significant Discovery (discoveries):
Episode 6: Plate Dynamics
What are tectonic plates? Describe their general motions.
Describe a divergent plate boundary, as exposed in Iceland.
How do divergent and convergent boundaries work to keep earth the same size?
Describe the 3 types of convergent plate boundaries. Give "real world" examples of each.
Why does oceanic crust sink below continental crust?
What 2 things happen as a subducting plate sinks back into the earth?
Why are convergent volcanoes more explosive than divergent (basaltic) volcanoes?
Describe the lithosphere and asthenosphere, and how they interact.
How do strain rate and temperature affect plastic deformation in the mantle?
What are mantle plumes?
What will happen when Hawaii drifts off the hot spot?
What questions remain about the theory of plate tectonics?
Give real-world examples of the different types of plate boundaries:
Divergent:
Ocean/ocean convergent:
Ocean/continental convergent:
Continental/continental convergent:
Transform: