READING QUESTIONS: Plate Tectonics
NAME________________________
PSCI 131
DUE: Monday, December 14th
Fall 2015
52 pts
Continental Drift: An Idea Before Its Time (p. 71-74)
1. List Alfred Wegener’s four lines of evidence for continental drift: (4 pts)
a. _______________________________________________________
b. _______________________________________________________
c. _______________________________________________________
d. _______________________________________________________
2. In the early 20th century, before continental drift, what were the three prevailing explanations for how
land animals migrated across large oceans? (3 pts)
a. ___________________________________________________________________________
b. ___________________________________________________________________________
c. ___________________________________________________________________________
3. Fill in the blanks: Wegener suggested that a plausible explanation for the late Paleozoic
________________ was provided by the supercontinent of ___________________. In this
configuration, the southern ________________________ are joined together and located near the
________________________. This would account for the conditions necessary to generate extensive
expanses of _______________________ over much of these landmasses. At the same time, this
geography would place today’s _________________________ continents nearer the
________________________ and account for the tropical _________________ that generated the vast
__________________________. (5 pts)
The Great Debate (p. 75-76)
4. What mechanism did Wegener propose for continental drift, and what objection did physicist Harold
Jeffreys have to this mechanism? (4 pts)
______________________________________________________________________________
______________________________________________________________________________
__________________________________________________________(more space on next page)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
5. Fill in the blanks: Wegener incorrectly suggested that the larger, sturdier continents
________________________ the thinner oceanic crust, much as ____________________________
cut through ice. No evidence existed to suggest that the ocean floor was _____________ enough to
permit passage of the continents without the continents being appreciably _____________________
in the process. (2 pts)
The Theory of Plate Tectonics (p. 76-78)
6. What major ocean floor feature did oceanographers discover the extent of after World War II?
_____________________________________
7. Next to each characteristic below, indicate whether it applies to continental lithosphere, oceanic
lithosphere, both kinds of lithosphere, or the asthenosphere. Indicate your choice by writing “C”, “O”,
“CO”, or “A” next to each characteristic. (3 pts)
a. Cool
_____
b. Warm _____
c. Flows _____
d. Bends or breaks
_____
e. Mafic in composition _____
f. Felsic in composition _____
8. Match the name of each type of plate boundary with the arrows that show the kind of motion that occurs
there. (3 pts)
a. Transform
___
A.
b. Divergent
___
B.
c. Convergent___
C.
Divergent Plate Boundaries and Seafloor Spreading (p. 78-81)
9. What is the average rate of seafloor spreading in modern oceans? _______ cm/year
10. Fill in the blanks: The primary reason for the ___________________ position of the oceanic ridge is
that newly created lithosphere is ______, which means it is ________________ than cooler rocks
found away from the ridge axis. (3 pts)
11. Examine figure 15 and fill in the blanks: Continental rifting occurs where plate motions produce
__________________ forces that ________ the lithosphere and promote upwelling in the mantle.
Stretching causes the brittle crust to ____________ into large ____________ that sink, generating a
________________. Continued spreading generates a long, narrow _______ similar to the presentday Red Sea. Eventually, an expansive _____________________ containing a centrally located
_________________ is formed by continued seafloor spreading. (4 pts)
Convergent Plate Boundaries and Subduction (p. 81-84)
12. Why does the global rate of lithosphere creation roughly balance with the rate of lithosphere destruction?
(2 pts)
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
13. Fill in the blanks: The angle at which an oceanic plate subducts depends largely on its _____ and
therefore its ________________. (2 pts)
14. List the three possible combinations of lithosphere types that can occur at a convergent boundary. (3 pts)
a. _______________________________
b. _______________________________
c. _______________________________
15. EXTRA CREDIT: List one geographic example of a modern volcanic island arc, and one example of a
continental volcanic arc. (2 pts)
a. Volcanic island arc: _______________________________
b. Continental volcanic arc: ______________________________
16. On page 81, the textbook refers to deep-ocean trenches as “surface manifestations” of subduction zones.
Why does the book use the word “surface” even though these trenches are located in the deepest parts of
the oceans? (2 pts)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
17. Oceanic lithosphere subducts because it is ____________________ than the asthenosphere beneath it.
18. Give a brief description of how the Himalayas formed, with reference to the buoyancy of continental
lithosphere. (3 pts)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Transform Plate Boundaries (p. 85-86)
19. On this diagram of a fracture zone along an oceanic ridge, label the segment of the zone that is an active
transform boundary by marking a “T” on one of the three blanks.
20. EXTRA CREDIT: List two examples of transform boundaries that cut through continental crust instead
of through ocean basins. (2 pts)
a. ________________________________________
b. ________________________________________
Testing the Plate Tectonics Model (p. 89-94)
21. What is the age of the oldest sediments recovered by deep-sea drilling? ______________________
22. Continental rocks have been discovered that are older than _____________________ years.
23. Fill in the blanks: Drill cores have revealed that sediments are almost entirely ___________ on the
crests of oceanic ____________, and that sediment thickness ______________ with increasing
distance from the ridge. This suggests that the age of the ocean crust _______________ the further
it is from an oceanic ridge. (2 pts)
24. Examine figure 32A on page 93. The white stripes indicate oceanic crust exhibiting normal magnetic
polarity, and the red stripes indicate reversed polarity. How many time intervals of reversed polarity are
represented by the oceanic crust in this figure? (Remember that, during each time interval of reversed or
normal polarity, two stripes of crust with that polarity are created along divergent boundaries.)
Number of time intervals of reversed polarity: ________