READING QUESTIONS: Plate Tectonics NAME________________________ GEOL 131 DUE: Tuesday, November 24th Fall 2015 58 pts All answers should be in your own words. Continental Drift: An Idea Before Its Time (p. 281-284) 1. What was the first piece of evidence that led scientists to suspect that many continents were once connected? (2 pts) ______________________________________________________________________________ ______________________________________________________________________________ 2. Explain why the discovery of fossils of Mesosaurus in South America and Africa, but nowhere else, supports the continental drift hypothesis. (3 pts) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 3. In the early 20th century, what were the three prevailing explanations for how land animals migrated across large oceans? (3 pts) a. ___________________________________________________________________________ b. ___________________________________________________________________________ c. ___________________________________________________________________________ 4. How did Wegener explain the presence of glaciers in southern continents at a time when areas in North America, Europe, and Asia supported tropical swamps? (2 pts) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ The Great Debate (p. 284-285) 5. What mechanism did Wegener propose for continental drift, and what objection did physicist Harold Jeffreys have to this mechanism? (4 pts) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 6. 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. 285-287) 7. What major ocean floor feature did oceanographers discover the extent of after World War II? _____________________________________ 8. 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 _____ 9. List any six of the seven largest lithospheric plates. (3 pts) a. _______________________________ b. _______________________________ c. _______________________________ d. _______________________________ e. _______________________________ f. _______________________________ 10. 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. 288-290) 11. What is the average rate of seafloor spreading in modern oceans? _______ cm/year 12. 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. 13. 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) 14. 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 present-day Red Sea. Eventually, an expansive _____________________ containing a centrally located _________________ is formed by continued seafloor spreading. (4 pts) Convergent Plate Boundaries and Subduction (p. 290-293) 15. Why does the global rate of lithosphere creation roughly balance with the rate of lithosphere destruction? (2 pts) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 16. Fill in the blanks: The angle at which an oceanic plate subducts depends largely on its _____ and therefore its ________________. (2 pts) 17. List the three possible combinations of lithosphere types that can occur at a convergent boundary. (3 pts) a. _______________________________ b. _______________________________ c. _______________________________ 18. 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: ______________________________ 19. On page 290, 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) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 20. Oceanic lithosphere subducts because it is ____________________ than the asthenosphere beneath it. 21. Give a brief description of how the Himalayas formed, with reference to the buoyancy of continental lithosphere. (3 pts) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Transform Plate Boundaries (p. 294-295) 22. 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. 23. 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. 298-303) 24. What is the age of the oldest sediments recovered by deep-sea drilling? ______________________ 25. Continental rocks have been discovered that are older than _____________________ years. 26. 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) 27. 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: ________ What Drives Plate Motion? (p. 305-307) 28. Give short descriptions of slab pull and ridge push. (4 pts) Slab pull: _____________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ Ridge push: ___________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 29. Which mechanism (slab pull or ridge push) is thought to contribute more to tectonic plate motion? _________________________