Points Earned: 0/1 Correct Answer: B Your Response: D 2. What is indicated by the yellow lines in the image above? A. A great unconformity, with sedimentary rocks above resting on older sedimentary rocks below. B. A great fault, where pull-apart action slid the upper rocks across the lower ones. C. A great unconformity, with sedimentary rocks above resting on metamorphic rocks below. D. A great fault, where push-together action shoved the upper rocks over the lower ones. E. An intrusion, with melted rocks squirted along the yellow line and then hardened. John Wesley Powell, of the United States Geological Survey, and the leader of the first boat trip through the Grand Canyon, called the feature marked by the yellow lines “The Great Unconformity”. It separates horizontal Paleozoic sedimentary rocks, above, from inclined Precambrian sedimentary rocks, below. Points Earned: 0/1 Correct Answer: A Your Response: D
3. One practical radioactive system used to date lava flows involves: A. The gas argon-40, which decays to solid potassium-40. B. The solid potassium-40, which decays to the solid grahamspanierum-41. C. The gas argon-40, which decays to the gas potassium-40. D. The solid potassium-40, which decays to the gas argon-40. E. The solid potassium-40, which decays to solid argon-40. Potassium-40 is common in solid minerals, and decays to produce the gas argon-40. And despite his great contributions to humanity, no one has named an isotope after Penn State’s president. Points Earned: 1/1 Correct Answer: D Your Response: D 4. The picture above shows a region of hard rock about six inches across from the Grand Canyon.
The shape and polish of the rock are interesting. It is likely that the rock: A. Was scratched and polished by motion along a fault, which helped open the Canyon so that weathering could lower the Canyon floor. B. Was scratched and polished by silt-laden river water, during carving of the Canyon by the Colorado River. C. Was scratched and polished by the hooves of mules carrying tourists into the Canyon along the Bright Angel Trail. D. Was scratched and polished by a glacier, which helped erode the Canyon during the ice age. E. Was scratched and polished by the wind, which howls through the Canyon carrying loads of sand eroded from sand bars. The Canyon was carved by the Colorado River. Glaciers have not been there, and while wind, faults and mule hooves all can change the appearance of rocks, none makes something like this river-polished rock, as we saw in class and you saw in one of the Grand Canyon slide shows. Points Earned: 0/1 Correct Answer: B Your Response: C 5. Which is accurate about the history of the Grand Canyon: A. The rock record of the canyon contains exactly one unconformity. B. The canyon is wider at the top and narrower at the bottom because the river was wider when the region was wetter, and has narrowed as deserts spread recently.
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