GRE Reading Comprehension

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Source: XDF

Theorists are divided concerning the origin of the Moon. Some hypothesize that the Moon was formed in the same way as were the planets in the inner solar system (Mercury, Venus, Mars, and Earth)—from planet-forming materials in the presolar nebula. But, unlike the cores of the inner planets, the Moon's core contains little or no iron, while the typical planet-forming materials were quite rich in iron. Other theorists propose that the Moon was ripped out of the Earth's rocky mantle by the Earth's collision with another large celestial body after much of the Earth's iron fell to its core. One problem with the collision hypothesis is the question of how a satellite formed in this way could have settled into the nearly circular orbit that the Moon has today. Fortunately, the collision hypothesis is testable. If it is true, the mantlerocks of the Moon and the Earth should be the same geochemically.

Question List: 1 2

The primary purpose of the passage is to

  • A present two hypotheses concerning the origin of the Moon
  • B discuss the strengths and weaknesses of the collision hypothesis concerning the origin of the Moon
  • C propose that hypotheses concerning the Moon's origin be tested
  • D argue that the Moon could not have been formed out of the typical planet-forming materials of the presolar nebula
  • E describe one reason why the Moon's geochemical makeup should resemble that of the Earth

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