GRE阅读机经解析 18

Passage 18

Massive projectiles striking much larger bodies create various kinds of craters, including “multi-ring basins”—the largest geologic features observed on planets and moons. In such collisions, the impactor is completely destroyed and its material is incorporated into the larger body. Collisions between bodies of comparable size, on the other hand, have very different consequences: one or both bodies might be entirely smashed, with mass from oneor both the bodies redistributed among new objects formed from the fragments. Such a titanic collision between Earth and a Mars-size impactor may have given rise to Earth’s Moon.

The Earth-moon system has always been perplexing. Earth is the only one of the inner planets with a large satellite, the orbit of which is neither in the equatorial plane of Earth nor in the plane in which the other planets lie. The Moon’s mean density is much lower than that of Earth but is about the same as that of Earth’s mantle. This similarity in density has long prompted speculation that the Moon split away from a rapidly rotating Earth, but this idea founders on two observations. In order to spin off the Moon, Earth would have had to rotate so fast that a day would have lasted less than three hours. Science offers no plausible explanation of how it could have slowed to its current rotational rate from that speed. Moreover, the Moon’s composition, though similar to that of Earth’s mantle, is not a precise match. Theorizing a titanic collision eliminates postulating a too-rapidly spinning Earth and accounts for the Moon’s peculiar composition. In a titanic collision model, the bulk of the Moon would have formed from a combination of material from the impactor and Earth’s mantle. Most of the earthly component would have been in the form of melted or vaporized matter. The difficulty in recondensing this vapor in Earth’s orbit, and its subsequent loss to the vacuum of outer space, might account for the observed absence in lunar rocks of certain readily vaporized compounds and elements.

Unusual features of some other planets might also be explained by such impacts. Mercury is known to have a high density in comparison with other rocky planets. A titanic impact could have stripped away a portion of its rocky mantle, leaving behind a metallic core whose density is out of proportion with the original ratio of rock to metal. A massive, glancing blow to Venus might have given it its anomalously slow spin and reversed direction of rotation. Such conjectures are tempting, but, since no early planet was immune to titanic impacts, they could be used indiscriminately to explain away in a cavalier fashion every unusual planetary characteristic. Still, we may now be beginning to discern the true role of titanic impacts in planetary history.

1. According to the passage, which of the following is true of the collisions mentioned in the highlighted sentence?

A. They occur less frequently than do titanic collisions.

B. They occur between bodies of comparable size.

C. They occur primarily between planet-sized bodies.

D. They result in the complete destruction of the impacting body.

E. They result in mass being redistributed among newly formed objects.

2. The author of the passage asserts which of the following about titanic collision models?

A. Such models are conclusive with respect to certain anomalies within the solar system, but leave numerous other anomalies unexplained.

B. Such models are more likely than are earlier models to account for the formation of multi-ring basins.

C. Such models may be particularly useful in explaining what happens when the impacting bodies involved are of highly dissimilar mean densities.

D. Such models have been tested to such a degree that they are quickly reaching the point where they can be considered definitive.

E. Such models are so tempting that they run the risk of being used indiscriminately to explain unusual planetary features.

3. The passage suggests that which of the following is true of the cited “compounds and elements”?

A. They were created by reactions that took place during a titanic collision.

B. They were supplied by an impactor that collided with Earth.

C. They were once present on the Moon but were subsequently vaporized.

D. They are rarely found on planet-size bodies in our solar system.

E. They are present on Earth but not on the Moon.

4. In the second paragraph, the author is primarily concerned with

A. arguing in favor of a particular theory about the formation of the Earth-Moon system.

B. summarizing conventional theories about the formation of the Earth-Moon system.

C. anticipating and responding to criticisms of particular theory about the formation of the Earth-Moon system.

D. explaining why the Earth-Moon system is considered scientifically perplexing.

E. questioning an assumption underlying one theory about the formation of the Earth-Moon system.

两类撞击，结果不同

一、小天体撞击大天体，小天体被吸收

二、类似大小天体相撞，新天体产生（例如地球的卫星，月球）

The Earth-Moon system has always been perplexing.

地月系统一直以来令人困惑。

Earth is the only one of the inner planets with a large satellite, the orbit of which is neither in the equatorial plane of Earth nor in the plane in which the other planets lie.

地球是唯一的带有大型卫星的内行星，其大型卫星的轨道既不在地球的赤道平面上，也不在其他行星所处的平面上。

The Moon’s mean density is much lower than that of Earth but is about the same as that of Earth’s mantle.

月球的平均密度远低于地球密度，但却几乎等同于地球地幔的密度。

This similarity in density has long prompted speculation that the Moon split away from a rapidly rotating Earth, but this idea founders on two observations.

这种密度上的相似性一直在引发相应的推测，即月球是从一个快速旋转的地球中分离出去而形成，但这一想法因两个观测而站不住脚。

In order to spin off the Moon, Earth would have had to rotate so fast that a day would have lasted less than three hours.

要能快速旋转以至于分离月球，地球很可能不得不以极快的速度旋转，以至于每日时长应小于3小时。

Science offers no plausible explanation of how it could have slowed to its current rotational rate from that speed.

科学无法提供可信解释来证明它如何从这样的高速减缓至当前的旋转速度。

Moreover, the Moon’s composition, though similar to that of Earth’s mantle, is not a precise match.

而且，月球的组成，虽然类似于地球地幔，却并非完全一致。

Theorizing a titanic collision eliminates postulating a too-rapidly spinning Earth and accounts for the Moon’s peculiar composition.

对大型撞击的理论推定，既排除了旋转过快的地球这一假设，也解释了月球的特殊构成。

In a titanic collision model, the bulk of the Moon would have formed from a combination of material from the impactor and Earth’s mantle.

从大型撞击模型来看，月球主体是由撞击天体与地球地幔材料的混合体形成。

Most of the earthly component would have been in the form of melted or vaporized matter.

大部分地球相关的成分很可能处于融化的液态或蒸发的气态。

The difficulty in recondensing this vapor in Earth’s orbit, and its subsequent loss to the vacuum of outer space, might account for the observed absence in lunar rocks of certain readily vaporized compounds and elements.

将这类气态物质重新凝结在地球轨道中非常之难，且其随后会流失在外太空的真空里；这或许解释了为何在月球岩石中无法观测到某些易于蒸发的化合物及元素。

Unusual features of some other planets might also be explained by such impacts.

其他行星上的不寻常特征或许也能通过这种撞击来解释。

Mercury is known to have a high density in comparison with other rocky planets.

目前已知，水星有着相较于其他多岩石的行星更高的密度。

A titanic impact could have stripped away a portion of its rocky mantle, leaving behind a metallic core whose density is out of proportion with the original ratio of rock to metal.

一次大型撞击可能会将其一部分岩石质的地幔剥离，而留下了一个金属质的内核。该内核的密度与原始的岩石金属比例不相称。

A massive, glancing blow to Venus might have given it its anomalously slow spin and reversed direction of rotation.

一次对金星的大型侧击或许导致了其异常缓慢的旋转速度和颠倒的旋转方向。

Such conjectures are tempting, but, since no early planet was immune to titanic impacts, they could be used indiscriminately to explain away in a cavalier fashion every unusual planetary characteristic;

这些推测虽然都很诱人，但是，因为没有任何的早期行星能够不受到大型撞击的影响，这类撞击可能会被随意地用于解释任何一种不寻常的行星特征。

Still, we may now be beginning to discern the true role of titanic impacts in planetary history.

我们此刻或许要仔细辨明这类大型撞击在行星历史中的真正作用。

1. According to the passage, which of the following is true of the collisions mentioned in the highlighted sentence?

A. They occur less frequently than do titanic collisions.

B. They occur between bodies of comparable size.

C. They occur primarily between planet-sized bodies.

D.They result in the complete destruction of the impacting body.

E. They result in mass being redistributed among newly formed objects.

选D

参考原文In such collisions, the impactor is completelydestroyed

2. The author of the passage asserts which of the following about titanic collision models?

A. Such models are conclusive with respect to certain anomalies within the solar system, but leave numerous other anomalies unexplained.

B. Such models are more likely than are earlier models to account for the formation of multi-ring basins.

C. Such models may be particularly useful in explaining what happens when the impacting bodies involved are of highly dissimilar mean densities.

D. Such models have been tested to such a degree that they are quickly reaching the point where they can be considered definitive.

E. Such models are so tempting that they run the risk of being used indiscriminately to explain unusual planetary features.

3. The passage suggests that which of the following is true of the cited compounds and elements?

A. They were created by reactions that took place during a titanic collision.

B. They were supplied by an impactor that collided with Earth.

C. They were once present on the Moon but were subsequently vaporized.

D. They are rarely found on planet-size bodies in our solar system.

E. They are present on Earth but not on the Moon.

4. In the second paragraph, the author is primarily concerned with

A. arguing in favor of a particular theory about the formation of the Earth-Moon system.

B. summarizing conventional theories about the formation of the earth-Moon system.

C. anticipating and responding to criticisms of a particular theory about the formation of the Earth-Moon system.

D. explaining why the Earth-Moon system is considered scientifically perplexing.

E. questioning an assumption underlying one theory about the formation of the Earth-Moon system.

选A，参考第二段简化