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ES Chap 17 Plate Tectonics
1. Describe early evidence that led people to suggest that Earth’s continents may have once been
2. Discuss evidence of continental drift.
3. Explain why continental drift was not accepted when it was first proposed.
4. Summarize the evidence that led to the discovery of seafloor spreading.
5. Describe the uses of magnometers and sonar.
6. Explain the significance of magnetic patterns on the seafloor.
7. Explain the process, cause, features and evidence of seafloor spreading.
8. Explain the theory of plate tectonics.
9. Compare & contrast the 3 types of plate boundaries and the features, location, & direction of
movement of each. (Features include: subduction, trenches, ridges, mountains, islands)
10. Explain the process of convection.
11. Summarize how convection in the mantle is related to the movements of tectonic plates.
12. Compare & contrast the processes of ridge push & slab pull.
13. Miscellaneous: Pangea, early mapmakers, Wegener
Sec 17.1 Drifting Continents
1. Early mapmakers noted that the ___________________of continents appeared to ______________
like a ________________________.
a. Gondwanaland: Thought _________________ continents were joined as a ____________
landmass at one time
2. Alfred Wegener proposed hypothesis of _________________________________
3. Continental Drift theory: ______ continents were originally joined as a ________________________
called _________________ and have drifted to their current locations.
4. Wegener’s evidence for continental drift:
a. __________________ fit of continents
b. Rocks: Similar rock types between:
i. _____________________mountains in _______ & rocks in _________________
ii. __________________________ & _________________________
c. Fossils:
i. Kannemeyerid & Labyrinthodonts were ___________________ animals that could
NOT have ________________________
ii. Mesosaurus: ____________________ reptile that could not have crossed the ocean
iii. Glossopteris: ________ found on many continents that have now have _____ climates
 Continents must have been joined & had a ______________________
climate to grow the fern
 Antarctica must have been closer to the _______________ to have a ____
enough climate to grow the fern
d. Climate data
i. _________deposits have been found in Antarctica
It forms from dead swamp plants. Swamps only occur in an area that is _________
 This indicates that Antarctica was once ______________________ and closer to the
ii. ________________deposits in Africa, India, South America, and Australia
This suggests that these areas were closer to the __________________ at one
5. Continental drift rejected in early 1900s due to 2 flaws.
a. Wegener couldn’t explain what caused the continents to ____________
b. Wegener couldn’t explain how the continents could move without ____________________
Sec 17.2 Seafloor Spreading
1. Ideas about the ocean floor were wrong until the mid-1900’s. Scientists thought the seafloor was flat,
older than continents, and unchanging-ALL WRONG
2. Sonar was a big advancement: Calculated the distance to the seafloor using the _________ it took
reflected ____________________ to return
3. Magnetometer: Measures small changes in ___________________ fields
a. Used to make maps of the _____________________ fields in ____________on the seafloor
4. Ocean floor topography
a. Ocean__________________contain the ______________mountain range on Earth
i. _______________________________ occur along the ridges
b. Deep-sea _______________ are narrow & elongated depressions w/very steep sides
i. Deepest trench: __________________trench is over 11km deep
5. Ocean rocks & sediments
a. Rocks near the ridges are the ___________________________, age increases with distance
from the ridge
b. Oceanic rocks are much ____________________ than continental rocks
c. Oceanic sediments are _____________________ than continental sediments
d. Thickness of sediments __________________with distance from the mid-ocean ridges
e. Paleomagnetism: magnetic record of rocks containing __________________
i. Basalt contains iron minerals which get “stuck” pointing towards Earth’s
_______________________ as it cools and hardens
ii. The iron minerals show a pattern of ____________________________which indicate
a change in Earth’s magnetic field
6. Seafloor spreading theory: _______ ocean crust is formed at ocean ridges & _____________ at
deep-sea trenches
a. Proposed by Harry Hess
b. Magma is ___________ & ________ dense at the midocean ridge, so it fills the gap in the
c. Magma in the gap _______________, forming new ocean floor
d. More & more magma rises & hardens, forcing the previous rock to move away from the ridge
e. Therefore, _______________ rock is near the ridge and age ______________ farther from
the ridge
Theory provided answers to the 2 flaws of Wegener’s continental drift hypothesis
i. Seafloor spreading caused the __________________________
ii. Landmasses didn’t shatter because because they weren’t plowing through the ocean
crust. Rather, the ocean floor & continents ________________________
Section 17.3 Theory of Plate Tectonics
The theory states that the Earth’s _____________________________________ are broken into
enormous slabs called __________________
1. Plates move in different __________________________ and at different ________________
Plate boundaries: 3 main types
1. Divergent Boundaries: Plates move ____________________--A. Forms rift valleys, mid-ocean ridges, volcanoes, earthquakes
B. Usually found on ____________________
Adds (creates ) ______________
Causes ocean basins to_____________________
C. Few found on land as _______________________________________________________
Divergent boundary:
2. Convergent Boundaries: Plates _________________ & move ___________________________
A. Subduction MAY occur: One plate ________________________________ the other
_______________________________ crust material
Due to differences in ________________
Creates deep-sea trenches, volcanoes & volcanic islands
Subducted plate descends into mantle & __________, magma rises & forms
volcanoes and/or island arcs
3 subtypes of Convergent Boundaries
A. Oceanic meets oceanic
 The _____________ & _______________ oceanic plate descends below the
_________________ oceanic plate
Forms deep-sea ____________, island ________, ______________ & ___________
Example locations:
 Mariana Trench & Islands
 Aleutian Islands near Alaska
 Japan & Philipines
B. Oceanic meets continental
 __________ocean plate descends below the ________________ continental plate
 Ocean plates are dense because they are made of ___________________
 Continental plates are less dense because they are made primarily of __________
Forms ________________________ along the edge of continents
Mountain ranges, volcanoes, deep focus earthquakes may occur along the continental
edge ______________________________________
Example locations: Peru-Chile trench & Andes Mountains along western
edge of ____________________________
C. Continental meets continental
Subduction ____________________________
 Both continental plates are too ___________________ due to
 Therefore, there is ____________________________________________
______________ mountain ranges, extremely folded
Earthquakes present
Example location: ____________________________
3. Transform Boundaries: 2 plates __________________________________ past each other
A. Crust is NEITHER consumed or created, only deformed or fractured
B. Creates long __________________ & ____________________ earthquakes
Fault = ________________ in Earth’s crust along which movement occurs
C. Can move __________________directions, OR the same direction at different ___________
D. Example locations: _____________________________ fault. Also along ocean ridges
Section 17.4 Causes of Plate Motions
Convection: The transfer of thermal energy by the movement of heated matter
1. Warms, _________________, and becomes _____________________ & ____________
2. __________________________ material sinks due to gravity
3. Forms a cycle, or _____________________________
Mantle Convection Currents in the Asthenosphere:
1. ________________in the aesthenosphere is thought to cause the plate movements
A. Aesthenosphere is a ____________________________ of the mantle that ________ &
allows the plates to move
B. Hot mantle material is less dense & rises, as it cools it sinks again
2. Rising part of current occurs at _________________________boundaries
A. Causes upward & lateral forces that __________________________________
B. As plates separate, rising ________________ cools & forms new ___________________
3. Sinking part of the current occurs at _____________________ boundaries, pulling the plate material
A. Sometimes forms ________________________
Computer Review:
a. Chapter Resources
b. Unit 5
c. Chapter 17
Convergent Boundary-3 subtypes
Divergent Boundary
Oceanic to oceanic
Oceanic to
Rift valley
Island arcs
Mountains-very high
Subduction zone &
deep sea trench
Example locations
Additional comments
Continental to