托福阅读真题+题目+答案：The Composition of Meteors

托福阅读真题+题目+答案：The Composition of Meteors

Meteors are tiny solid particles that enter Earth’s atmosphere from interplanetary space. Since the particles move at speeds of many kilometers per second, friction with the air vaporizes them at altitudes between 80 and 130 kilometers. The resulting flashes of light fade out within a few seconds. These“shooting stars” got their name because at night their luminous vapors look like stars moving rapidly across the sky. Some meteorites do end up landing on Earth’s surface. It was not until the time when meteorites were measured and their compositions analyzed in detail that scientists appreciated their true significance. The meteorites include the oldest and most primitive materials available for direct study in the laboratory.

1. The word “luminous” in paragraph 1 is closest in meaning to

A. Beautiful

B. Sweeping

C. Glowing

D. Dark

2. According to paragraph 1, which of the following is true?

A. Most meteorites fall to Earth’s surface after they are vaporized

B. Large particles that come together from interplanetary space form what is called a meteor

C. Meteors are vaporized due to friction at heights of about 100 kilometers

D. Flashes of light seen in the sky at night are falling stars, which we refer to as shooting stars

The average age for the most primitive meteorites, calculated using the most accurate values now available for radioactive half-lives, is 4.5 billion years. This value is taken to represent the age of the solar system—the time since the first solids condensed and began to form into larger bodies.

3. What can be inferred from the information in paragraph two?

A. Most meteorites are primitive meteorites

B. The solar system is roughly 4.5 billion years old

C. Astronomers prefer to study primitive meteorites since they are older

D. Scientists have utilized new technology to assess the age of primitive meteorites

Meteorites are often classified between primitive and differentiated meteorites. The differentiated meteorites are fragments of larger parent bodies that were molten before they broke up, allowing the denser materials (such as metals) to sink to their centers. Like many rocks on Earth, they have been subject to a degree of chemical reshuffling, with the different materials sorted according to density. Differentiated meteorites include the irons, which come from the metal cores of their parent bodies;stony-irons, which probably originate in regions between a metal core and a stony mantle; and some stones that are composed of mantle or crust material from their differentiated parent bodies.

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