E. Sample I is from near the river, and sample II is from high in the cliffs of the Grand Canyon. Sample I is a wonderful shell hash, or coquina, from the Supai Rocks well up the side of theCanyon, and contains shells from a great diversity of different creatures. Sample II includesalgal-mat deposits (stromatolites) from the Precambrian Chuar Group of the Grand Canyon Supergroup, deep in the Canyon near the river, from a time when biology was not a whole lot more diverse than algal mats. Points Earned: 0/1 Correct Answer: D Your Response: A 3. Geological evidence based on several radiometric techniques has provided a scientifically well- accepted age for the Earth. Represent that age of the Earth as the 100-yard length of a football field, and any time interval can be represented as some distance on
the field. (So something that lasted one-tenth of the age of the Earth would be ten yards, and something that lasted one-half of the age of the Earth would be fifty yards.) On this scale, how long have you been alive? A. 1 yard.B. 10 yards.C. 1 inch.D. 50 yards.E. Much less than the thickness of a sheet of paper. If the 4.6 billion years of Earth history are 100 yards, then the few thousand years of written history are just one-millionth of that history, just over the thickness of a sheet of paper. And your small piece of written history must be only a small fraction of a sheet of paper, roughly 1/200th or so. Points Earned: 0/1 Correct Answer: E Your Response: B A.
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 a glacier, which helped erode the Canyon during the ice age. B.Was scratched and polished by the wind, which howls through the Canyon carrying loads of sand eroded from sand bars. 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 motion along a fault, which helped open the Canyon so that weathering could lower the Canyon floor. E.Was scratched and polished by silt-laden river water, during carving of the Canyon by the Colorado River. 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 GrandCanyon slide shows. Points Earned: 0/1 Correct Answer: E
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