READING QUESTIONS: Plate TectonicsGEOL131Winter 2017

NAME______DUE: Tuesday,April 11th 61pts

Continental Drift: An Idea Before Its Time (p. 281-284)

  1. Fill in the blanks in this sentence from the textbook (p. 281): “The idea that ______,

particularly ______and ______, fit together like pieces of a

jigsaw puzzle came about during the ______, as better ______

became available.” (5 pts)

  1. Fill in the blanks in these sentences from the textbook (p. 282): “…it was when [Wegener] learned that

identical ______had been discovered in rocks from both South

America and Africa that his pursuit of ______became more
focused…Wegener learned that most paleontologists…were in agreement that some type of
______was needed to explain the existence of similar Mesozoic-age
life forms on widely ______landmasses.” (4 pts)

  1. In the early 20th century, how did opponents of the continental drift hypothesis explain the presence of identical fossils on separate continents? (3 pts)
  1. ______
  2. ______
  3. ______
  1. Fill in the blanks in these sentences from the textbook (p. 283): “…evidence for a ______
    period had been discovered in southern ______, ______,
    ______, and ______. This meant that about 300 million years ago, vast ice
    sheets covered extensive portions of the Southern Hemisphere as well as India. Much of the land
    that contains evidence of this period of Paleozoic glaciation presently lies within 30° of the
    ______in ______or ______climates.” (4 pts)

The Great Debate (p. 284-285)

  1. What mechanism did Wegener propose for continental drift, and what objection did physicist Harold Jeffreys have to this mechanism? (4 pts)

______

______

______

______

______

______

  1. Fill in the blanks in these sentences from the textbook (p. 285): “Wegener…incorrectly suggested

that the larger and sturdier continents ______the thinner oceanic crust, much

as ______cut through ice. However, 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.” (4 pts)

The Theory of Plate Tectonics (p. 285-287)

  1. What major ocean floor feature did oceanographers discover the extent of after World War II?

______

  1. 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)
  1. Cool_____
  2. Warm_____
  3. Flows _____
  4. Bends or breaks_____
  5. Mafic in composition_____
  6. Felsic in composition_____
  1. Match the name of each type of plate boundary with the arrows that show the kind of motion that occurs there. (3 pts)

Transform___A.

Divergent___B.

Convergent___C.

Divergent Plate Boundaries and Seafloor Spreading (p. 288-290)

  1. What is the average rate of seafloor spreading in modern oceans? ______cm/year
  1. EXTRA CREDIT: All of Earth’s modern ocean floors were created at divergent boundaries within the last 200 million years. Although this seems like a long time, it is only ______% of Earth history.
  1. Fill in the blanks in this sentence from the textbook (p. 289): “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)
  1. Fill in the blanks in these sentences from the textbook (Fig. 14, p. 289): “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 present-day Red Sea.

Eventually, an expansive ______containing a centrally located

______is formed by continued seafloor spreading.” (4pts)

Convergent Plate Boundaries and Subduction (p. 290-293)

  1. Fill in the blanks: The angle at which an oceanic plate subducts depends largely on its _____ and
    therefore its ______. (2 pts)
  1. Match each of the following types of convergent plate boundary to the correct diagram (3 pts):

Oceanic-oceanic_____

Oceanic-continental_____

Continental-continental_____

  1. B.
  1. EXTRA CREDIT: List one geographic example of a modern volcanic island arc, and one example of a continental volcanic arc. (2 pts)
  2. Volcanic island arc: ______
  3. Continental volcanic arc: ______
  4. Oceanic lithosphere subducts because it is ______than the asthenosphere beneath it.

Transform Plate Boundaries (p. 294-295)

  1. On this diagram of a fracture zone along an oceanic ridge, label the segment of the zone that is an active transform boundary by writing “transform” on one of the three blanks.

  1. EXTRA CREDIT: List two examples of transform boundaries that cut through continental crust instead of through ocean basins. (2 pts)
  2. ______
  3. ______

Testing the Plate Tectonics Model (p. 298-303)

  1. What is the age of the oldest sediments recovered by deep-sea drilling? ______
  1. Continental rocks have been discovered that are older than ______years.
  1. Fill in the blanks in these sentences from the textbook (p. 298): Drill cores…revealed that sediments
    are almost entirely ______from the ______, and that sediment
    thickness ______with increasing distance from the ridge.” (3 pts)
  1. Examine Figure 27 on page 299. In which direction do the Hawaiian Islands become older? (North is toward the top of the figure.)
  2. Southeast
  3. North
  4. Northwest
  5. Southwest
  6. Your answer to the previous question means that the Pacific tectonic plate, on which Hawaii sits, is moving
  7. Southeast
  8. North
  9. Northwest
  10. Southwest
  11. Fill in the blanks in these sentences from the textbook (p. 300): “…some naturally occurring
    minerals are ______and are influenced by Earth’s ______
    ______. One of the most common is the iron-rich mineral ______, which is
    abundant in ______of basaltic composition…as the lava cools, these iron-
    rich grains become magnetized and ______themselves in the direction of the existing magnetic
    ______of ______. Once the minerals solidify, the magnetism they possess usually
    remains “______” in this position. Thus, they act like a ______
    because they “point” toward the position of the magnetic ______at the time of their
    formation. Rocks that formed thousands or millions of years ago and contain a “______” of
    the direction of the magnetic poles at the time of their formation are said to possess
    ______.” (6 pts)
  1. Examine figure 31 on page 302. 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: ______

  1. Examine Figure 33 on page 304. The youngest ocean floor is closely associated with what ocean floor feature?
  2. Oceanic ridges
  3. Subduction zones
  4. Seamounts
  5. Continental margins
  6. All of the above
  7. None of the above