WATER AND LIFE ON MARS
1 The presence or absence of water has a direct bearing on the possibility of life on other planets. In the nineteenth century, it was commonly accepted that life, perhaps even intelligent life, was widespread in the solar system, and Mars was an obvious target in the search for life. New photographic technology offered a way for astronomers to learn more about the red planet. In 1888, Italian astronomer Giovanni Schiaparelli produced images that showed a network of long, thin, dark lines crossing the surface of Mars. He called these features canali in Italian, which became “canals” or “channels” in English. The strange appearance of the canals suggested to some scientists that they had been formed artificially rather than naturally. The mystery deepened when Schiaparelli observed that many of the canals in the photographs were actually double.
2 Other photographic images of Mars revealed its seasonally changing polar ice caps and features that appeared to be ancient islands located in what was now a dry streambed. When the islands were first discovered, some scientists speculated that a thick water-laden atmosphere capable of generating heavy rains had once existed on Mars. However, others remained unconvinced of the presence of water. Then, in 1963, a team of astronomers obtained a good photographic plate of the near-infrared spectrum of Mars. The photograph showed that, faintly but definitely, water vapor lines could be seen. This photograph established that there really was water on Mars, though the amount was very small. Today, the presence of water vapor in the Martian atmosphere is generally accepted, as is the belief that the atmosphere was once much denser than it is now, with a much greater abundance of water vapor.
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3 The surface of Mars is dry today, but it does contain significant amounts of ice and signs that liquid water once flowed over the planet. All of the locations where evidence of water has been found are ancient, probably formed very early in Martian history. Data transmitted from spacecraft on Mars in 2004 have revealed that water was once common across a vast region of the planet, possibly as shallow lakes or seas that dried out and then filled up again. There are signs that the wind blew debris around during dry stages. These seas and lakes extended across hundreds of thousands of square miles, creating habitable conditions during long stretches of time billions of years ago.
4 Evidence of water includes the presence of various minerals known as evaporates, deposits left behind when liquid water turns to vapor. Small areas of mineral deposits have been found in Valles Marineris, a huge hole on Mars that is larger than the Grand Canyon on Earth. The minerals there contain water, so they had to be formed in the presence of water. Geologic research has also turned up clay and gypsum deposits that were formed by water in the soil. Rocks that clearly formed in water extend throughout 300 meters of layered materials in several locations across the Martian plains. The layers were built up over time, which means water was present, at least temporarily, for extended periods on ancient Mars.
5 Besides the ice packs at Mars’s poles, astronomers have discovered a frozen sea near its equator. This frozen sea is the size of the North Sea on Earth and appears similar to the ice packs on Antarctica. Scientists have also detected evidence of lava flows 20 million years ago as well as signs that some volcanoes may still be active. Several recently formed volcanic cones near Mars’s North Pole indicate that the planet’s core may interact with the surface, meaning there was both warmth and moisture in the recent past—circumstances that might have supported life.
6 Liquid water is the key ingredient for life as we know it. Of all the other planets in the solar system, Mars is most like Earth. The fact that water existed on ancient Mars does not necessarily mean life ever emerged there; however, all of the available evidence does suggest that Mars meets all the requirements that are needed for life to exist.
51. According to the passage, what has been a major focus of research about Mars?
(A) How Mars compares to other planets in the solar system
(B) Who built the network of canals on the surface of Mars
(C) Whether signs of water indicate that life has existed on Mars
(D) How soon astronauts from Earth will be able to go to Mars
52. Astronomers of the nineteenth and twentieth centuries studied Mars mainly through
(A) ancient writings
(B) photographic images
(C) Martian soil samples
(D) data sent by spacecraft
53. It can be inferred from paragraph 1 that Schiaparelli’s observation of canals on Mars led to
(A) direct proof that life has existed on Mars
(B) the rejection of Schiaparelli’s ideas by other scientists
(C) the search for canals on other planets in the solar system
(D) new questions about intelligent life on Mars
54. What discovery led some scientists to think that the Martian atmosphere had produced heavy rains in the past?
(A) A network of canals on the surface
(B) Ancient islands in a dry streambed
(C) Water vapor lines on a photographic plate
(D) Volcanic cones near the planet’s North Pole
55. Which sentence below best expresses the essential information in the highlighted sentence in paragraph 2? Incorrect choices change the meaning in important ways or leave out essential information.
(A) Most scientists believe there is water vapor in the Martian atmosphere, which is now less dense than it was in the past.
(B) The amount of water vapor in the Martian atmosphere has changed many times in the past, and scientists generally accept this.
(C) The atmosphere of Mars used to contain only water vapor, but now scientists know that several other gases are also present.
(D) Scientists used to believe that Mars had no atmosphere, but now most think it has a very dense atmosphere of water vapor.
56. The phrase filled up in paragraph 3 is closest in meaning to
(A) got smaller
(B) were frozen
(C) became wet
(D) turned to rock
57. The word habitable in paragraph 3 is closest in meaning to
(B) suitable for life
(D) capable of changing
58. Layers of rock in several places on the Martian plains are evidence that
(A) Mars was formed at the same time as Earth
(B) both wind and water erosion occurred there
(C) water was present there for a long time
(D) liquid water is no longer present on Mars
59. All of the following indicate the presence of water on Mars EXCEPT
(A) images of polar ice caps
(B) a 1963 photograph
(C) clay and gypsum deposits
(D) evidence of lava flows
60. The word ingredient in paragraph 6 is closest in meaning to
61. Why does the author compare Mars to Earth in paragraph 6?
(A) TO emphasize that there is more water on Earth than on Mars
(B) To point out that Mars has the conditions for life to exist
(C) To state that there are no differences between Mars and Earth
(D) To explain why life emerged on Earth but not on Mars
62. Look at the four squares, [A], [B], [C], [D] which indicate where the following sentence could be added to the passage. Where would the sentence best fit?
Astronomers already knew that Mars had some kind of atmosphere because of the occasional presence of bright features that looked like clouds.
The presence or absence of water has a direct bearing on the possibility of life on other planets. [A] In the nineteenth century, it was commonly accepted that life, perhaps even intelligent life, was widespread in the solar system, and Mars was an obvious target in the search for life. [B] New photographic technology offered a way for astronomers to learn more about the red planet. In 1888, Italian astronomer Giovanni Schiaparelli produced images that showed a network of long, thin, dark lines crossing the surface of Mars. [C] He called these features canali in Italian, which became “canals” or “channels” in English. The strange appearance of the canals suggested to some scientists that they had been formed artificially rather than naturally. [D] The mystery deepened when Schiaparelli observed that many of the canals in the photographs were actually double.
63. Read the first sentence of a summary of the passage. 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 long searched for evidence of water and life on Mars.
(A) Early photographs of Mars showed what appeared to be canals, polar ice caps, and ancient islands.
(B) Dry streambeds, lakes, and seas suggest that Mars does not have enough water to support life.
(C) The Martian atmosphere contains water vapor, and liquid water once flowed over the planet’s surface.
(D) Evaporates are mineral deposits that are left behind when liquid water turns to vapor.
(E) Mineral deposits and a frozen sea provide evidence of water on Mars in the past and present.
(F) Because Mars is so similar to Earth, scientists believe that humans will be able to live on Mars in the future.