Problem: You may be wondering, how can a glacier get so big? Why does it move? These are both good questions. In the winter months, precipitation falls as snow. This solid form of water builds up on the ground as long as the temperatures stay cold enough. As the temperature rises, the snow starts to melt. The frozen water changes state back into a liquid state. Nearer the poles, summer does not last very long. If the summer is long enough and warm enough, all the snow may melt. This is what typically happens now. The earth was a little cooler 12,000 years ago. As a result, during the summer months, that amount of snow did not melt. It may have only been an inch or so of snow that melted. The following winter, snow fell on top of this left-over snow. This next winters snowfall had a head start. Year after year, the snow that did not melt became thicker and thicker. Inch by inch the snow started to build up. Over many years, layer upon layer of snow compacted and turned to ice.

Question: "How does the snow turn into ice?"

Answer: "Year after year, the snow that did not melt became thicker and thicker, building up, compacting, and turning into ice"

OPTIONS:
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- yes
Answer: yes

Problem: Fossils can be used to match up rock layers. As organisms change over time, they look different. Older fossils will look different than younger fossils. Some organisms only survived for a short time before going extinct. Knowing what organisms looked like at certain times also helps date rock layers. Some fossils are better than others for this use. The fossils that are very distinct at certain times of Earths history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure 2.30. If two rock layers have the same index fossils, then they're probably about the same age.

Question: "What helps to date rock layers?"

Answer: "Chemical abalysis of rock substances"

OPTIONS:
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- yes
Answer: no

Problem: What a time of it Dawson's Landing was having! All its life it had been asleep, but now it hardly got a chance for a nod, so swiftly did big events and crashing surprises come along in one another's wake: Friday morning, first glimpse of Real Nobility, also grand reception at Aunt Patsy Cooper's, also great robber raid; Friday evening, dramatic kicking of the heir of the chief citizen in presence of four hundred people; Saturday morning, emergence as practicing lawyer of the long-submerged Pudd'nhead Wilson; Saturday night, duel between chief citizen and titled stranger. The people took more pride in the duel than in all the other events put together, perhaps. It was a glory to their town to have such a thing happen there. In their eyes the principals had reached the summit of human honor. Everybody paid homage to their names; their praises were in all mouths. Even the duelists' subordinates came in for a handsome share of the public approbation: wherefore Pudd'nhead Wilson was suddenly become a man of consequence. When asked to run for the mayoralty Saturday night, he was risking defeat, but Sunday morning found him a made man and his success assured.

Question: "Whose names and praises were in everyone's mouths?"

Answer: "The principals of the duel"

OPTIONS:
- no
- yes
Answer:
yes