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According to the United States Geological Survey, the T. rex responsible for this track was probablymoving 6 or 7 miles per hour. A mature T. rex would have been about 60 feet long, two stories high,and 10,000 pounds or so, quite capable of making a 33-inch-long, 9-inch-deep track in mud. Points Earned: 2.0/2.0Correct Answer(s):A5.
You are a geologist. While walking in the fog one day, you bang into a cliff. After rubbing your sorenose, you inspect the cliff, and see what is shown in the picture, in a one-foot-square area. You recognize that this cliff is made of “fossil sand dunes”, with wind-blown sand that was later glued together by hard-water deposits. You are accompanied by a student, who is carrying your tea and crumpets for you. You sketch four arrows on the cliff, label them as shown, and ask the student which of the arrows was pointing up when the loose sand was deposited. Your student is brilliant, and correctly tells you the answer. The arrow that was pointing up when the loose sand was deposited is the arrow that is closest to: A) A B) B C) C D) DFeedback: Several small sand dunes are visible in this picture. Originally, the whole picture was rotated so the D was up and the B down. The first deposit was made by wind blowing from the C to the A, putting down slightly slanting layers in the lee of a dune; these layers are behind the B now. Then, the wind eroded away the top of the dune, cutting the layers, and then new sand was depositedon top of the cut ends of the layers. The cut ends must be up, where the wind could reach them, which tells you that the D side was originally up.
Points Earned: 2.0/2.0Correct Answer(s):D6. You are still a geologist, still wandering around in a fog with a tea-and-crumpets-toting student, and you walk into another cliff. This one turns out to be a hardened lava flow. Again, you look at a one-foot-square region, sketch pink arrows with A, B, C, and D on that region, and ask the student whichof the pink arrows was pointing up just after the lava flow hardened. To help the student, you draw four additional arrows on the cliff; these are light blue (turquoise) arrows, pointing at bubbles. (If you are not able to distinguish pink from light blue, the four pink arrows are very close to the four letters A, B, C, and D, and the four light-blue arrows are not close to the letters.) You suggest that the student consider the behavior of bubbles in a liquid. These bubbles are within the lava flow, and not in the crust on top of the flow that was chilled very rapidly by the air. Your student is brilliant, and correctly tells you the answer. The pink arrow (close to a letter) that was pointing up when the lava flowed in and slowly cooled is the arrow that is closest to: A) A B) B
C) C D) DFeedback: Below the frozen upper crust of a lava flow, bubbles tend to rise, and they tend to grow as they rise because less pressure squeezes them near the top of the flow, and because they pick up dissolved gas from the flow as they rise. So, you expect a big-bubble layer near the top and a little-