托福阅读真题+题目+答案：Chondrites

托福阅读真题+题目+答案：Chondrites

Meteorites are the keys to understanding how Earth and the solar system formed because, although superficially many meteorites do not look significantly different from most Earth rocks close study shows that they are very different, With those differences holding clues to their distant origin. The most common type of meteorite-known collectively as the"chondrites-contains clues about the kinds of material that went into the construction of our planet.

1.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information

O To understand how our solar system formed, it is important to determine the differences between Earth rocks and meteorites

O Despite their similar outward appearance, meteorites and Earth rocks are really very different, and the differences help explain how our solar system formed

O The superficial similarity of meteorites to Earth rocks provides clues about how our solar system formed

O While meteorites had a distant origin, their presence on Earth is a key to understanding how our solar system formed

The chondrites are just one of a variety of meteorite types, all ancient, but each with a different history-and each containing clues about how Earth and other planets formed and evolved. For example, the members of one group, the iron meteorites, are made up of solid iron metal, alloyed (or mixed )with a modest amount of nickel All the evidence indicates that these meteorites are similar to the metallic cores that inhabit the interiors of planets.

2.According to the information in paragraph 2, which of the following is true about iron meteorites?

O They are much more ancient than the chondrites

O They are less similar to planets' metallic cores than chondrites

O They came to Earth from other planets

O They are solid metal objects

In contrast to the iron meteorites. the chondrites are made up of a jumble of mineral grains, many of them familiar constituents of rocks on Earth, but also including pure iron metal-which does not occur in rocks on Earth-and small marble-like spherical objects called"chondrules"(it is from these that the chondrites take their name). The chaotic texture of chondrites indicates that they were formed in a process that randomly swept together their different components and cemented them together. The texture is also an instant clue to one of their most important characteristics: they have never been melted. Furthermore, mineral grains in the chondrites have provided the oldest ages ever measured by radiometric dating they date from the very earliest days of the solar system. These two properties have led the geochemists who work on these intriguing objects to conclude that chondrites bring us something we cannot find on Earth or among other meteorite varieties: an unprocessed sample of the original material from which Earth and our neighboring planets were made. They appear to be unaltered samples of the solid matter that was floating around in the solar system just as Earth was being born; there is strong evidence that they come from small asteroids that never grew big enough to heat up and melt, as larger objects did.

3.The word "chaotic" in the passage is closest in meaning to

O characteristic

O disorganized

O smooth

O unusual

4.According to paragraph 3, which of the following is indicated by the texture of chondrites?

O They were formed by the same process as the rocks on Earth

O They are made of metals and minerals of different ages

O They have never been melted

O They are held together by a marble-like material

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