4. Starting with a supercontinent, order the following tectonic actions of the Wilson cycle from oldest (1) to most recent (4)

Transcription

1 Geology 101 Sample final exam (Chapters 1 9, 13, 16) Open textbook, notes, handouts, labs, field trip module, group projects, midterm exams, calculators. No collaboration. 100 points total, two hours. Short answer (2 points each) Answer all questions 1. The size of a continental plate with no oceanic lithosphere will (choose one): a. shrink over time because of convergent boundaries at its edges b. grow over time because of sea-floor spreading c. stay the same because there s no spreading and subduction doesn t alter its size 2. Biotite schist is (choose one): a. an igneous rock with some biotite b. a mineral with some biotite c. a sedimentary rock with some biotite d. a metamorphic rock with some biotite 3. Hotspots can be active for millions of years because (choose one): a. Convection cells within the mantle and lower crust are fairly stable over time. b. Convection will keep bringing hot mantle material towards the surface. c. The second law of thermodynamics is a fundamental principal of science. d. Plate tectonics has been running for millions of years. 4. Starting with a supercontinent, order the following tectonic actions of the Wilson cycle from oldest (1) to most recent (4) Continent-continent collision Sea floor spreading Continental rifting Subduction zone formation 5. Which of the following rocks can be turned into an igneous rock (choose all that apply): a. sedimentary rock b. igneous rock c. metamorphic rock d. none of these 6. Order the following events from oldest (1) to most recent (4) that occurred in the Seattle area during the last ice age. The deposition of a pro-glacial lake sediment throughout the Seattle area The deposition of meltwater stream sediment in the Puget Sound outwash plain The deposition of unsorted sediment as the glacier retreated from Seattle The creation of the linear north-south ridges throughout the Seattle area

2 7. The Issaquah Alps (including Cougar and Tiger Mountains) orogeny is: a. volcanic b. horst-and-graben c. fold-and-thrust The following questions are worth 4 points each. 8. How can you tell the numerical age of a leaf imprint? (choose all that are correct) a. radiocarbon (carbon-14) dating the imprint b. uranium-dating the sediment the imprint is found in c. potassium-argon dating any ash layers above and below the imprint d. identification of the particular plant species and referencing its numerical age from paleontological studies 9. How do you distinguish subduction zones from continental collision zones? (choose all that are correct) a. Look for the presence of folded rocks. b. Look for volcanoes. c. Look for blueschist. d. Look for uplifted sedimentary rocks. Rock type identification section (12 points) 10. Western Washington contains a large number of dark fine-grained rocks. In the sample bins at the front of the classroom are three different rocks, labeled with colored tape: one is metamorphic, one is sedimentary and one is igneous. Identify which rock is which rock type, write an observation that supports your answer, and, for an extra credit point each, name each rock. The blue-tape rock is: The red-tape rock is: The purple-tape rock is: Drawing a cross-section section (10 points) 11. Draw a cross-section from Essay section part one Each of the following student answers has one or more errors in the answer. Identify the error(s) and fix it (them). Choose two of the three questions and circle the number; give answers in complete sentences. These questions are worth 8 points each.

3 12. The stratigraphic column below shows a cross-section of sedimentary rock found in Zion Canyon in Utah. At the base of the sequence is a marine limestone; above it, there is a shale, and above that is a sandy shale, with a bedded sandstone capping the whole sequence. What changes in the sediment s source area or in the sedimentary environment could have been responsible for this sequence? This is not a one-word answer; describe the different depositional environments/water energies that this area experienced. Student answer: The limestone is at the bottom of the column so there was still water this area was a lake. Then the river started flowing in this area, slowly, which deposited shale, and the river picked up speed, and deposited sandy shale, then finally the sand. 13. Choose two minerals that you think might make good abrasive or grinding stones for sharpening steel, and describe the physical property that causes you to believe that they would be suitable for that purpose. Student answer: Orthoclase and plagioclase would be great for sharpening because these minerals are some of the most common minerals on the Earth s surface; you can pick up most any rock and use it as a sharpening stone. 14. If the magnetic anomaly stripes on the ocean floor are formed parallel to spreading ridges and if spreading ridges are linear, how do magnetic stripes bend? Student answer: The bend in the magnetic stripes shows a change in the plate s motion. The stripes will change direction exactly the same way that the plate direction changes. Essay section part two Choose two of the three questions and circle the number; give answers in complete sentences. These questions are worth 8 points each. Note that all these questions are taken from the labs.

4 15. Lab 7: The cross-section above is exposed in a deep canyon of the Deschutes River and you find a fossil trilobite near the top of layer E and a fossil ammonite near the top of layer G. Suppose further a research team finds the numerical ages of the dikes to be 40 million years (My) for the younger one and 220 My for the older one. Is the numerical date of the younger dike consistent or inconsistent with the paleontological age ranges of the fossils? Explain why. 16. Lab 5: You have a sample of preserved ripple marks. They are symmetrical with a wavelength of about 3 centimeters. Is it more likely that these ripples were originally deposited in a desert, a river, or a tidal flat? Explain your answer. How are they preserved so that you can see them today? 17. Lab 4: Thundereggs are a type of geode, which make beautiful bookends and household decorations. The exterior rock of these thundereggs, which are from the Priday Agate Beds near Redmond, Oregon, is an andesitic basalt, and the interior material is milky quartz. Write a short history of how this rock came to be; in other words, start from magma and tell me what happened to make this rock. Hint: it s not a one-event history. Essay section part three Choose two of the three questions and circle the number; give answers in complete sentences. Each question is worth 12 points. 18. In many areas where petroleum formed, seas also dried up long ago, leaving evaporite deposits containing the organic remains of the organisms that used to live in those seas. Given the following observations: Evaporite minerals absorb water and oxygen readily but do not release them Evaporite minerals are less dense than surrounding rock Evaporite minerals do not dissolve in oil Explain how evaporite deposits can form a trap for oil. You must use the words rise, impermeable and oxygen-free, as well as all three observations, in your answer.

5 19. About 35 km down into the Earth below your feet, P-wave velocities increase abruptly from about 6 km/s (as you used in Lab 9) above that depth to 8 km/s below that depth. This is called the Mohorivicic discontinuity (or Moho) in honor of its discoverer. a. Give a reason why the speed changes so abruptly. Hint: 35 km is thickness of most continents. b. Would the Moho be deeper, shallower or the same depth if you were standing on the deep Pacific Ocean floor? Give a reason for your answer. 20. The graph on the next page shows the change in the New Zealand Southern Alps ELAs over the past few decades (note the x-axis timeline runs from 1950 to 2005). Using only the Alps Cumulative ELA line (the line with the white circles that starts in 1975): a. In general, what has happened to the Alps cumulative ELA over the last thirty years? What does this imply about the general climate conditions in New Zealand over the last thirty years? b. The trend that you noted in part a is not uniform; the graph has peaks and valleys. Given that the average temperature in the New Zealand Southern Alps has steadily increased (no decreases at all) over the last thirty years, how can the fluctuations in the Alps cumulative ELA be explained? Hint: what factors go into building a glacier?