2015年3月14日托福阅读真题P2+题目+答案：The Origin of Earth's Atmosphere

2015年3月14日托福阅读真题P2+题目+答案：The Origin of Earth's Atmosphere

1. In order to understand the origin of Earth's atmosphere, we must go back to the earliest days of the solar system, before the planets themselves were formed from a disk of rocky material spinning around the young Sun. This material gradually coalesced into lumps called planetesimals as gravity and chance smashed smaller pieces together, a chaotic and violent process that became more so as planetesimals grew in size and gravitational pull. Within each orbit, collisions between planetesimals generated immense heat and energy. How violent these processes were is suggested by the odd tilt and spin of many of the planets, which indicate that each of the planets was, like a billiard ball, struck at some stage by another large body of some kind. Visual evidence of these processes can be seen by looking at the Moon. Because the Moon has no atmosphere, its surface is not subject to erosion, so it retains the marks of its early history. Its face is deeply scarred by millions of meteoric impacts, as you can see on a clear night with a pair of binoculars. The early Earth did not have much of an atmosphere. Before it grew to full size, its gravitational pull was insufficient to prevent gases from drifting off into space, while the solar wind (the great stream of atomic particles emitted from the Sun) had already driven away much of the gaseous material from the inner orbits of the solar system. So we must imagine the early Earth as a mixture of rocky materials, metals, and trapped gases, subject to constant bombardment by smaller planetesimals and without much of an atmosphere.

1..The word chaotic in the passage is closest in meaning to

A. rapid

B. disorganized

C. intense

D. long-lasting

2..All of the following are true of the planetesimals mentioned in paragraph 1 EXCEPT:

A. They were formed of rocky material spinning around the early Sun.

B. They collided violently with each other.

C. They gradually grew in size.

D. They lost their atmospheres as they were hit by larger bodies.

3..The word retains in the passage is closest in meaning to

A. reveals

B. acquires

C. hides

D. preserves

4..The author discusses the Moon in paragraph 1 in order to

A. help explain why Earth had fewer meteoric impacts than other planets in the solar system

B. show why it is difficult to understand how the first planetary atmospheres developed

C. help explain the processes that took place in the formation of large planetary bodies in the solar system

D. illustrate why the Moon's spin and tilt are unique among other planetary bodies in the solar system

5..The word constant in the passage is closest in meaning to

A. considerable

B. unpredictable

C. continual

D. violent

2. As it began to reach full size, Earth heated up, partly because of collisions with other planetesimals and partly because of increasing internal pressures as it grew in size. In addition, the early Earth contained abundant radioactive materials, also a source of heat. As Earth heated up, its interior melted. Within the molten interior, under the influence of gravity, different elements were sorted out by density. By about 40 million years after the formation of the solar system, most of the heavier metallic elements in the early Earth, such as iron and nickel, had sunk through the hot sludge to the center, giving Earth a core dominated by iron.This metallic core gives Earth its characteristic magnetic field, which has played an extremely important role in the history of our planet.

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