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12.The picture above shows a region of hard rock about six inches across from the GrandCanyon. The shape and polish of the rock are interesting.It is likely that the rock:A.Was scratched and polished by the hoof mules carrying tourists into the Caalong the Bright Angel Trail.B.Was scratched and polished by a glacier, which helped erode the Canyon durithe ice age.C.Was scratched and polished by motion along a fault, which helped open the Canyon so that weathering could lower the Canyon floor.D.Was scratched and polished by the wind, which howls through the Canyon carrying loads of sand eroded from sand bars.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 Grand Canyon slide shows.Correct Answer:EYour Response:EPoints Earned:1/113.The two pictures above, I and II, show fossils in rocks from the Grand Canyon. Each is "typical"; the rocks near sample I contain fossils similar to those shown in sample I, and the rocks near sample II contain fossils similar to those shown in sample II. It is likely that:
Points Earned:1/114.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 is written history?