GEOL/METR 309: Investigating
Land, Sea and Air Interactions

Fall 2005, SFSU

Reading Assignment #5,
Part I: The Theory
of Plate Tectonics (CD)

Dr. Dave Dempsey
Dr. Lisa White
(Dept. of Geosciences)

(For class on Tuesday, Oct. 4)


Introduction. The questions under "Reading Questions" below are based on the intermediate version of Tarbuck and Lutgens, "The Theory of Plate Tectonics" (version 2.01), 2003, Tasa Graphic Arts. Inc., Chapters 1-6 (on CD). (Part II of this assignment will focus on the remaining chapters.) These questions are designed to help you focus on what we think are some of the most important parts of these chapters. Although you don't need to hand in your answers to these questions, answering them should help you prepare for an in-class exercise that you will have to turn in for credit, as well as Exam #2.

As a prelude to this reading assignment, we first summarize features of the global patterns of earthquakes, volcanoes, and topographic features that we discovered during the in-class activities referred to in the "Objectives" section above. Then you'll read through the first six chapters of the intermediate version of Tarbuck and Lutgens, "The Theory of Plate Tectonics" (version 2.01, on CD), looking for answers to the reading questions while watching for ways in which the theory of plate tectonics might help explain the patterns of earthquake, volcano, and topographic feature distributions that we identified earlier.

Review and Recap. In the in-class activities on global distributions of earthquakes and volcanoes, we discovered that there are systematic global patterns of earthquake locations and depths, active volcano locations, and topographic features such as mountains and deep-sea trenches. Moreover, there are strong associations between most of these patterns. In particular, we discovered that:




Reading Questions

Based on the first six chapters of the intermediate version of Tarbuck and Lutgens, "The Theory of Plate Tectonics" (version 2.01), 2003, on CD:

  1. Introduction
    1. What is plate tectonics?

  2. Continental Drift: An Idea Before Its Time
    1. What was Pangaea? When did it exist? What happened to it?
    2. In the early part of the 20th century, what were four types of evidence that Alfred Wegener cited in support of his theory of continental drift? Give a specific example of each.
    3. How can we explain similar fossils in rocks around the world that are older than 200 million years (my), and fossil diversity in rocks younger than 200 my?
    4. How can we explain (1) evidence for tropical forests in ancient rocks found today in cold northern regions; and (2) evidence of glaciation in ancient rocks found today in tropical regions?
    5. What was one of the reasons why Wegener's ideas were not widely accepted at the time he proposed them?

  3. Exploring Continental Drift
              (This is a review chapter. If you like, try your hand at reconstructing Pangaea; test your knowledge of world geography; practice using longitude as a measure of position east and west on the earth; and become more familiar with the positions of continents and creation of ocean basins since Pangaea began breaking up.)

  4. Earth's Interior
    1. Geologists divide the earth's interior into four layers, like layers of an onion. What are these four layers, and what distinguishes each of them from the others?
    2. The outermost layer of the earth (which is also by far the thinnest) is the crust. It consists of continental crust and oceanic crust. In continental crust, what is one of the most common types of rock (among many)? What is the most common type of rock found in oceanic crust? (One of these rock types is volcanic igneous and the other plutonic igneous—which is which?)
    3. Which is thicker (that is, deeper from top to bottom)—continental crust or oceanic crust? Which is denser (and hence tends to lie lower on the earth's surface than the other)?
    4. Geologists also divide the upper portion of the earth's interior into two layers, the asthenosphere and the lithosphere, which differ from the four layers that you identified in (a) above because different criteria are used to define them. The lithosphere contains the crust and part of the upper mantle, while the asthenosphere, which lies beneath the lithosphere, contains some more of the upper mantle. What characteristics distinguish the lithosphere from the asthenosphere?

  5. New Evidence: Mapping the Ocean Floor
    1. In the 1950s and 1960s, what topographic features of the ocean floor did mapping done using echo sounding technology reveal?
    2. What ocean bottom feature tends to be associated with active volcanoes?

  6. Plate Tectonics: A Scientific Revolution Unfolds
    1. When did the theory of plate tectonics finally emerge from the earlier theory of continental drift? (One of your instructors remember when this was taking place, though he was just a kid—it was a major and very exciting development in the world of science at the time, and it occurred at the same time as the U.S. was preparing to try to land a person on the moon.)
    2. What allows the seven major lithospheric plates (and several other smaller plates) to move around? (Lithospheric plates are also called tectonic plates, or just plates.)
    3. Do these lithospheric plates consist either exclusively of continental land mass or exclusively of ocean floor? If not, can you cite an example?
    4. With respect to lithospheric plates, where do most earthquakes, volcanoes, and mountain building occur?
    5. What are the three types of plate boundaries? At each type of boundary, what are the motions of the plates relative to each other?
    6. Are all three types of boundaries ever found around the periphery of any single plate?

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