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29 Cards in this Set
- Front
- Back
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Alfred Wegener…The Continental Drift Hypothesis
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The fit of S. America & W. Africa
Assembled all continents together: Pangea Laurasia (north) Gondwanaland (south) Fossil evidence Glacial deposits Folded rock belts across ocean |
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Continental Drift
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The idea that a single supercontinent broke apart and pieces drifted away
No plausible mechanism One thought: the land masses plowed thru ocean crust like a ship on ice Or that continental crust simply slid over ocean crust Neither well received Idea shelved until 1960 |
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Crust
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thinnest layer
Oceanic Continental |
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Mantle
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Uniform composition
Varying rock strength w/ depth |
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The Earth's Layers
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Lithosphere – crust + rigid upper mantle
Asthenosphere – hot, plastic-like mantle Base of mantle – strong again Core – outer liquid, inner solid, both Ni-Fe |
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the Sea-Florr Spreading hypothesis
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Mid-Oceanic Ridge system
Found after WWII Mid-Atlantic Ridge Magnetic polarity stripes (normal / reversed) Mud thickness (thin at ridge) |
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The Theory of Plate Tectonics
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Plate boundary – fracture separating plates
Divergent – moving apart Convergent – coming together Transform – moving past one another Divergent boundaries – new crust formed Ocean-ocean (ridges) Continent-continent (rift valleys) |
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The Theory of Plate Tectonics (CONT)
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Convergent – old crust subducted
Ocean – Ocean arcs & trenches Ocean – Continent mountains & trenches Continent – Continent mountains |
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The Theory of Plate Tectonics (CONT)
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Transform boundaries – sliding by
Ocean – Ocean offsets ridge system Continent – Continent deformed mountain range, fault deformations |
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The Anatomy of a Tectonic Plate
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Segment of lithosphere
May include oceanic and/or continental crust Hard, mechanically strong Floats atop asthenosphere Margin is tectonically active Moves slowly (1-16 cm/yr) |
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Why Plates Move: The Earth as a Heat Engine
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Convection – heating / cooling fluids
Soup pot Mantle plumes – rising column of hot mantle rock Hot spots – shallow heating |
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Supercontinents
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Before 2 bya, few / no large continents, mainly island arcs
2-1.8 bya, arcs swept together by plate motions into 1 continent, broke apart ~1 bya, drifting formed another landmass that broke back apart again |
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Isostasy: Vertical Movements of the Lithosphere
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A buoyancy-like effect
When lithosphere mass changes, it may rise or fall Floating in equilibrium |
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How Plate Movements Affect Earth Systems
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Volcanoes – magma rising to surface
Divergent zones Convergent zones Earthquakes – motions at all boundaries Mountain building – thicker crust Subduction zones Rift zones Migrating continents & oceans As plates move, so do features atop |
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1. Alfred Wegener named the northern part of the supercontinent __________ consisting of what is now North America and Eurasia.
a. Pangea b. Laurasia c. Gondwanaland d. Arctica |
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2. Average oceanic crust is __________ kilometers thick, whereas average continental crust is __________ kilometers thick.
a. 20 to 40, 5 to 10 b. 50 to 100, 200 to 400 c. 4 to 7, 20 to 40 d. 200 to 400, 50 to 100 |
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3. The mantle makes up about __________ percent of the Earth’s volume.
a. 8 b. 80 c. 20 d. 0.8 |
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4. The asthenosphere extends from a depth of about __________ km down to a depth of about __________ km below the surface of the Earth.
a. 1, 3.5 b. 10, 35 c. 100, 350 d. 1000, 3500 |
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5. The __________ includes Earth’s crust and the uppermost strong and rigid part of the mantle.
a. lithosphere b. asthenosphere c. atmosphere d. biosphere |
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6. __________ have occurred on average every 500,000 years over the past 65 million years of Earth’s history.
a. Supercontinents b. Major mass extinctions c. Banded iron formations d. Magnetic reversals |
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7. Magnetic orientation in rocks that is opposite to the current orientation of Earth’s magnetic field is called __________ magnetic polarity.
a. normal b. reversed c. regular d. irregular |
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8. Where two plates move horizontally toward each other, they form a __________ boundary.
a. convergent b. rift c. divergent d. transform |
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9. The Himalayan Mountain Range is an example of a __________ boundary.
a. convergent b. divergent c. transform d. rift valley |
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10. Where two lithospheric plates of different densities converge, the denser one sinks into the mantle beneath the other in a process called __________.
a. submission b. subduction c. rifting d. spreading |
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11. The entire mantle–lithosphere system circulates in great __________ cells.
a. spreading b. reversal c. plume d. convection |
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12. Tectonic plates typically move at rates of 1 to 16 __________ per year.
a. millimeters b. meters c. centimeters d. kilometers |
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13. The first supercontinent formed by collisions of microcontinents and island arcs probably about __________ years ago.
a. 4.5 billion b. 2 to 1.8 billion c. 543 million d. 5 million |
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14. According to the theory of isostasy, the __________ is in floating equilibrium on the __________.
a. core, asthenosphere b. asthenosphere, mantle c. lithosphere, asthenosphere d. inner core, outer core |
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15. A mantle plume is a __________.
a. convergent boundary between two plates b. divergent boundary between two plates c. transform boundary between two plates d. rising column of hot, plastic mantle rock |
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