The Composition of Meteors

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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.

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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.

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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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For information on the earliest history of the solar system, we turn to the primitive meteorites—those made of materials that have not been subject to great heat or pressure since their formation. We can look at the spectrum of sunlight reflected from asteroids and compare their compositions with those of primitive meteorites. Such analysis indicates that their parent bodies are almost certainly asteroids. Since

asteroids are believed to be fragments left over from the formation process of the solar system, it makes sense that they should be the parent bodies of the primitive meteorites.

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The great majority of the meteorites that reach Earth are primitive stones. Many of them are composed of light-colored gray silicates with some metallic grains mixed in. Among the most useful of these meteorites have been the Allende meteorite that fell in Mexico, the Murchison meteorite that fell in Australia, and the Tagish Lake meteorite that landed in a winter snowdrift on Tagish Lake, Canada, in 2000.

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The Murchison meteorite is known for the variety of organic chemicals it has yielded. Most of the carbon compounds in carbonaceous meteorites are complex, tar-like substances that defy exact analysis. Murchison also contains 16 amino acids (the building blocks of proteins), 11 of which are rare on Earth. The most remarkable thing about these organic molecules is that they include equal numbers with right-handed and left-handed molecular symmetry. Amino acids can have either kind of symmetry, but all life on Earth has evolved using only the left-handed versions to make proteins. The presence of both kinds of amino acids clearly demonstrates that the ones in the meteorites had an extraterrestrial origin.

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These naturally occurring amino acids and other complex organic molecules in Murchison—formed without the benefit of the sheltering environment of planet Earth—show that a great deal of interesting chemistry must have taken place when the solar system was forming. If so, then perhaps some of the molecular building blocks of life on Earth were first delivered by primitive meteorites and comets. This is an interesting idea because our planet was probably much too hot for any organic materials to survive its earliest history. But after Earth’s surface cooled the asteroid and comet fragments that pelted it could have refreshed its supply of organic materials.

Source: Fraknoi, A., Morrison, D., & Wolff, S. C. (2016).

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Reading Paragraph 1

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.

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

a. Beautiful

b. Sweeping

c. Glowing

d. Dark

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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

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Section

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Reading Paragraph 2

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.

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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

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Reading Paragraph 3

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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4. All of the following are true EXCEPT

a. Differentiated meteorites come from larger objects which were made of molten originally

b. There are only two classes of meteorites: primitive and differentiated

c. Meteorites composed of molten metals tend to have heavier materials in its center

d. Among the differentiated meteorites are the irons and stony-irons

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Reading Paragraph 4

For information on the earliest history of the solar system, we turn to the primitive meteorites—those made of materials that have not been subject to great heat or pressure since their formation. We can look at the spectrum of sunlight reflected from asteroids and compare their compositions with those of primitive meteorites. Such analysis indicates that their parent bodies are almost certainly asteroids. Since

asteroids are believed to be fragments left over from the formation process of the solar system, it makes sense that they should be the parent bodies of the primitive meteorites.

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5. According to paragraph 4, how can we learn about the solar system’s earliest history?

a. By looking at the composition of differentiated meteorites

b. From looking at images of primitive meteorites when they are attached to parent asteroids

c. By studying asteroids and the parent bodies of both differentiated and primitive meteorites

d. By comparing the makeup of primitive meteorites to that of asteroids seen through the reflection of sunlight

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Reading Paragraph 5

The great majority of the meteorites that reach Earth are primitive stones. Many of them are composed of light-colored gray silicates with some metallic grains mixed in. Among the most useful of these meteorites have been the Allende meteorite that fell in Mexico, the Murchison meteorite that fell in Australia, and the Tagish Lake meteorite that landed in a winter snowdrift on Tagish Lake, Canada, in 2000.

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6. Why does the author say that the Allende, the Murchison, and the Tagish Lake meteorites were“among the most useful”?

a. To explain that these meteorites provide scientists with the most information

b. To suggest that these meteorites were the most intact of all that have fallen to Earth

c. To point out the countries that recovered the most information

d. To show that there have not been many useful fallen meteorites since 2000

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Reading Paragraph 6

The Murchison meteorite is known for the variety of organic chemicals it has yielded. Most of the carbon compounds in carbonaceous meteorites are complex, tar-like substances that defy exact analysis. Murchison also contains 16 amino acids (the building blocks of proteins), 11 of which are rare on Earth. The most remarkable thing about these organic molecules is that they include equal numbers with right-handed and left-handed molecular symmetry. Amino acids can have either kind of symmetry, but all life on Earth has evolved using only the left-handed versions to make proteins. The presence of both kinds of amino acids clearly demonstrates that the ones in the meteorites had an extraterrestrial origin.

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7. According to paragraph 6, what is so notable about the Murchison meteorite?

a. It was made entirely of carbon compounds that could not be analyzed

b. It had within it sixteen amino acids which are rare to find on Earth

c. It was of extraterrestrial origin and contained an unmatched symmetry

d. It contained eleven rare amino acids that included a unique molecular symmetry

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Reading Paragraph 7

These naturally occurring amino acids and other complex organic molecules in Murchison—formed without the benefit of the sheltering environment of planet Earth—show that a great deal of interesting chemistry must have taken place when the solar system was forming.?If so, then perhaps some of the molecular building blocks of life on Earth were first delivered by primitive meteorites and comets. This is an interesting idea because our planet was probably much too hot for any organic materials to survive its earliest history. But after Earth’s surface cooled the asteroid and comet fragments that pelted it could have refreshed its supply of organic materials.

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8. Which of the following best expresses the essential information in the highlighted sentence in paragraph 7? Incorrect choices change the meaning in important ways or leave out essential information.

a. The amino acids and organic molecules found in the Murchison meteorite occur naturally

b. The amino acids and organic molecules in the Murchison meteorite tell us a lot about the chemistry of the formation of the solar system

c. The Murchison meteorite was formed in space so the chemical processes were different

d. The amino acids and organic molecules contained within the Murchison meteorite would be different had they been formed on Earth

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9. Look at the four squares (A, B, C, D) that indicate where the following sentence could be added to the passage.

Some have been more helpful than others in providing information about the solar system.

Where would the sentence best fit?

A The great majority of the meteorites that reach Earth are primitive stones. B Many of them are composed of light-colored gray silicates with some metallic grains mixed in. C Among the most useful of these meteorites have been the Allende meteorite that fell in Mexico, the Murchison meteorite that fell in Australia, and the Tagish Lake meteorite that landed in a winter snowdrift on Tagish Lake, Canada, in 2000. D

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10. DIRECTIONS: An introductory sentence for a brief summary of the passage is provided below.

Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Scientists have found that meteors and their chemical composition reveal a great deal regarding our solar system.

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a. Meteorites that have fallen to Earth have helped us gain a better understanding of the universe

b. Primitive meteorites and their chemical makeup have provided an approximate age of the solar system at 4.5 billion years

c. Meteorites that are vaporized by friction are referred to as “shooting stars”

d. The two most common classes of meteorites are differentiated and primitive meteorites

e. Scientists learned a lot about the chemistry of the formation of the solar system by studying the composition of fallen meteors

f. The majority of meteorites that have landed on Earth are classified as differentiated meteorites

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