Chapter_19_test

							                    CHAPTER 19: The Search for Extraterrestrial Life


1. One of the great lessons being learned from modern astronomy is that
   A) we occupy a unique position in the universe, and nowhere else are we likely to
         find conditions equivalent to those in our solar system.
   B) our position and circumstances in the universe are quite ordinary and certainly not
         unique.
   C) the chemistry, geology, and physics on the Earth are unique to our planet, and the
         behavior of matter anywhere else appears to be significantly different from that on
         the Earth.
   D) we live at the center of a very massive black hole and all the observed
         cosmological effects such as redshift and cosmic background radiation and even
         the evolution of life are a consequence of the unique position that we occupy.
   Ans: B
   Section: 19-1

2. Why is liquid water believed to be essential to the development of life on a planet or
   other body?
   A) It provides an electrically conducting medium in which lightning currents can
         create complex organic molecules.
   B) It is a fluid and therefore provides a physical medium in which the building blocks
         of life can move around and get together.
   C) Without water there would be no shoreline onto which primitive fish could crawl
         to begin life on land.
   D) It combines chemically with other compounds to form the building blocks of life.
   Ans: B
   Section: 19-1

3. Why is the strategy of searches for extraterrestrial life usually based on a carbon
   chemistry?
   A) Carbon dioxide is the main ingredient of planetary atmospheres, both terrestrial
         and Jovian.
   B) No other atom can combine easily with the abundant hydrogen and helium to
         form long molecules in interstellar gas.
   C) Most meteorites that reach Earth are composed of carbon.
   D) Carbon is abundant and is versatile in forming complex, long-chain molecules.
   Ans: D
   Section: 19-1




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4. Why is it highly likely that life, should it exist elsewhere in the universe than just on the
   Earth, will be based on carbon chemistry?
   A) Because carbon can bond with many more atomic species in a wider variety of
         complex forms than other equivalent elements, such as silicon
   B) Because carbon combines more readily than other atoms with nitrogen, the major
         component of atmospheres such as that of Earth, to produce complex molecules
   C) Because carbon is expected to be far more abundant than silicon or other like
         elements that can combine to produce complex molecules
   D) Because carbon releases more energy than most other atoms when it combines
         with oxygen, thereby providing the energy for life processes in living organisms
   Ans: A
   Section: 19-1

5. Which of the following statements is NOT considered to be a reason why carbon is
   thought to be the element on which complex extraterrestrial life is likely to be based?
   A) It forms chemical bonds that are both strong and flexible.
   B) Every life-form on the Earth is carbon-based, over an immense range of
         conditions.
   C) It releases a significant amount of energy when it combines with hydrogen.
   D) It provides a basis for forming long, complex chains of molecules.
   Ans: C
   Section: 19-1

6. In which type of meteorite has evidence been found for organic molecules, some of
   which, in contrast to most life molecules on the Earth, have both right- and left-hand
   spiral structure?
   A) Iron meteorite                             C) Stony meteorite
   B) Stony-iron meteorite                       D) Carbonaceous chondrite
   Ans: D
   Section: 19-1

7. Which type of meteorite was found to contain large organic molecules that make up the
   building blocks of life and provide strong evidence for their extraterrestrial production?
   A) Iron meteorites                            C) Carboneous chondrites
   B) Stony-iron meteorites                      D) Stony meteorites
   Ans: C
   Section: 19-1




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 8. Several lines of evidence now suggest that large and complex organic molecules can
    exist or could evolve in outer space, from which the building blocks of life could be
    formed. Which of the following is NOT one of these observational findings?
    A) Radio astronomical observations of large organic molecules in giant molecular
           clouds
    B) The discovery of organic molecules inside some meteorites
    C) The discovery by the Viking landers of large organic molecules in the Martian
           regolith
    D) Laboratory experiments in which electrical sparks passing through a combination
           of simple gases such as H2O, H2, N2, and CO2 produced large organic molecules
    Ans: C
    Section: 7-14 and 19-1

 9. Which wavelength range in the electromagnetic spectrum has been the most fruitful in
    the search for complex organic molecules in space?
    A) Infrared radiation
    B) Visible radiation
    C) UV radiation
    D) Microwaves and short-wavelength radio waves
    Ans: D
    Section: 19-1

10. In which of the following environments have long-chain carbon-based molecules not
    been found?
    A) Inside meteorites
    B) In massive interstellar clouds of gas and dust
    C) On the surface of the Earth
    D) On the surfaces of planets and moons such as Venus and Jupiter's moon Callisto
    Ans: D
    Section: 19-1

11. What source of energy was used to trigger the manufacture of complex organic
    compounds in laboratory simulations of conditions in primordial planetary
    atmospheres?
    A) Thermal heating, to simulate volcanic heating
    B) Electric discharges, to simulate lightning
    C) Heat from chemical reactions in early reactive planetary atmospheres
    D) UV and visible radiation, to simulate the intensity of sunlight at earlier times in
          planetary life
    Ans: B
    Section: 19-1




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12. The Miller-Urey “experiment” consisted of
    A) sending a coded message via radio toward nearby stars that are similar to the Sun
          and may have planets.
    B) attaching a metal plaque to the Voyager spacecraft to tell extraterrestrial beings
          about us, should they ever recover the spacecraft.
    C) monitoring tens of millions of radio frequencies at once in an effort to detect
          extraterrestrial radio communications.
    D) passing an electrical arc through a mixture of hydrogen, ammonia, methane, and
          water and looking for resulting organic compounds.
    Ans: D
    Section: 19-1

13. The basic chemical molecules thought to have been present in abundance in the early
    planetary system, and which were used in the classical Urey-Miller laboratory
    experiments in which complex compounds essential to life were formed by electric
    discharges, were
    A) CO2 (carbon dioxide), H2O (water), and H2 (hydrogen).
    B) H2 (hydrogen), O2 (oxygen), and CO2 (carbon dioxide).
    C) CH4 (methane), NH3 (ammonia), H2O (water), and H2 (hydrogen).
    D) H2 (hydrogen), He (helium), Ar (argon), and Ne (neon).
    Ans: C
    Section: 19-1

14. The classical laboratory experiments performed by Urey and Miller in order to explore
    the necessary conditions for the production of organic molecules (the building blocks of
    living things) in the solar system involved the passing of electrical discharges through
    what mixure of gases?
    A) Ammonia, methane, water vapor, and hydrogen
    B) Carbon dioxide, water vapor, and dust
    C) Hydrogen and helium
    D) Nitrogen, oxygen, water vapor, and carbon dioxide
    Ans: A
    Section: 19-1

15. Modern laboratory experiments, which repeated those of Urey and Miller in exploring
    the possibility of producing organic molecules (the building blocks of life) from
    mixtures of gases expected to exist in the early planetary system, passed electrical
    discharges through which mixture of gases?
    A) Nitrogen, hydrogen, water vapor, and carbon dioxide
    B) Ammonia, methane, water vapor, and hydrogen
    C) Hydrogen and helium
    D) Carbon dioxide, water vapor, and dust
    Ans: A
    Section: 19-1 and Figure 19-4




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16. Which of the following was probably NOT a source of large organic molecules, the
    “building blocks” of life, on the early Earth?
    A) Comets
    B) Meteorites
    C) Lightning flashes in the early terrestrial atmosphere
    D) Volcanic eruptions
    Ans: D
    Section: 19-1

17. Which of the following observations regarding the likelihood of life existing elsewhere
    in the universe has NOT yet been made?
    A) Discovery of assemblies of organic molecules into cell-like, self-replicating
           structures in the soils of Mars and the atmosphere of Venus
    B) Discovery of long-chain carbon-based molecules in interstellar clouds by radio
           astronomers
    C) The manufacture of organic compounds in laboratory simulations of primordial
           planetary atmospheres
    D) Discovery of long-chain amino acid protein molecules in meteorites
    Ans: A
    Section: 19-1

18. The primary constituents for the organic molecules needed for life do not include which
    one of the following?
    A) Oxygen        B) Sulfur     C) Carbon      D) Silicon
    Ans: D
    Section: 19-1

19. Which location in the solar system seems to be the only one capable of fostering an
    advanced civilization?
    A) Titan, a moon of Saturn                  C) Callisto, a moon of Jupiter
    B) Europa, a moon of Jupiter                D) the Earth
    Ans: D
    Section: 19-2




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20. Which of the following ideas has been borne out by actual astronomical observations
    over the past few centuries?
    A) The probability of life existing elsewhere in the universe, even elsewhere in our
          own solar system, is extremely great.
    B) We appear to occupy a unique position in the universe, unrepeated anywhere,
          since our Sun is unique in properties and position in a remarkable galaxy.
    C) All the observational evidence so far suggests that conditions for the evolution of
          life exist only on our Earth, in its position near our Sun.
    D) Our Sun is an unremarkable star in a commonplace galaxy, and many similar stars
          exist in the universe around which life might evolve on planets.
    Ans: D
    Section: 19-2 and Chapters 11, 15, and 16

21. In which of the following very harsh environments has life not been found on the Earth?
    A) Deep inside the Earth's crust
    B) In a lake locked far under the Antarctic ice pack
    C) In the hot water within geothermal vents on the ocean floor
    D) Life has been found in all of the environments listed here
    Ans: D
    Section: 19-2

22. Scientists are now targeting Europa, one of Jupiter's moons, as a likely site for searching
    for elementary life-forms because
    A) radio signals that follow a recognizable pattern have been detected from this
           moon.
    B) there appears to be large amounts of dark organic material spread on its surface.
    C) changes seen in the dark lines crossing the icy surface have a spectral signature of
           vegetation.
    D) there is strong evidence for liquid water beneath the thick ice layer on its surface.
    Ans: D
    Section: 19-2

23. On which of the following objects in our planetary system is it LEAST likely that life
    exists or existed at an earlier time?
    A) Mars                                     C) Europa, a moon of Jupiter
    B) Callisto, a moon of Jupiter              D) Io, a moon of Jupiter
    Ans: D
    Section: 8-4, 8-5, 8-7, and 19-2




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24. If we succeed in being able to communicate with other civilizations in space, which
    method of communication will prove to be the fastest?
    A) Nuclear powered rockets since we can then use unlimited power to accelerate
          these systems to almost infinite speeds
    B) None since the speed of light can never be exceeded by anything in our universe,
          thereby setting the communication speed limit
    C) Laser light since this single wavelength light can be directed into an extremely
          narrow and intense beam and can therefore be made to travel much faster than
          ordinary light
    D) Neutrinos because a modulated beam of these particles can penetrate almost
          anything very easily and can be made to travel almost infinitely fast.
    Ans: B
    Section: 14-1 and 19-3

25. Why was the discovery of pulsars initially misinterpreted as evidence of intelligent life
    elsewhere in the universe?
    A) It was not thought possible for a “natural” radio source to produce the rapid and
          extremely regular radio pulses detected from space.
    B) Radio telescopes occasionally detected the same sequence of five musical notes,
          which were then whistled or hummed regularly by all the people associated with
          these telescopes (D, E, C, lower C, and G on a piano).
    C) Pulses arriving from several nearby star systems showed Doppler shifts of
          frequency apparently caused by orbital motion of their source around the central
          stars, as if coming from planets.
    D) The rate of pulses detected from space appeared to contain primitive coding
          similar to a crude Morse Code.
    Ans: A
    Section: 13-10 and 19-3

26. What is the current status of our search for inhabitable, Earthlike planets circling other
    stars?
    A) Two stars have been found with Earth-mass planets orbiting at a distance suitable
           for liquid water and life, but we cannot yet see if they have oxygen-rich
           atmospheres.
    B) Many extrasolar planets have been discovered, but most are in orbits with
           eccentricities too high to provide a stable environment for life.
    C) No extrasolar planets of any kind have yet been confirmed.
    D) Planets have been detected orbiting other stars, but none of these appear to be
           suitable for life.
    Ans: D
    Section: 5-6, 5-7, and 19-3




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27. To what do the letters SETI refer?
    A) Search for Evidence of Terrestrial-planet Inhabitants
    B) Search for Extra-Terrestrial Intelligence
    C) Search for Extra-Terrestrial Invaders
    D) Sourcebook of Extrasensory Transient Incidents
    Ans: B
    Section: 19-3

28. Most searches of space for evidence of intelligent life concentrate on radio wavelengths
    because
    A) our atmosphere is most transparent at these wavelengths and such signals will be
          more easily detected from the Earth.
    B) radio energy is least affected by dust and gas in the interstellar medium.
    C) it is likely that extraterrestrial beings will have developed radio transmitters
          before more complex lasers or IR light transmitters.
    D) radio signals can carry the greatest amount of information per unit of time, so
          information transfer will be most efficient at these wavelengths.
    Ans: B
    Section: 19-3

29. The so-called water-hole, a region of the radio spectrum chosen for searches for signals
    from intelligent life because galactic and Earth-based noise and atmospheric absorption
    are at a minimum, is so-named because
    A) water vapor (H2O) has an intense laserlike emission line at this wavelength that
           extraterrestrials might use to communicate with us.
    B) two astronomically important wavelengths, the 21-cm line of H and a line from
           the hydroxyl radical OH, are in this region, the letters H and OH signifying water.
    C) water vapor emissions from planets at this wavelength will be a good indicator of
           life on other planets since water is essential for life as we know it.
    D) water vapor absorption in our atmosphere reaches a sharp minimum at this
           wavelength.
    Ans: B
    Section: 19-3

30. What strategies and electromagnetic frequencies are thought to be the most logical for
    long-range communication across the universe with other intelligent beings?
    A) Explosion of nuclear devices at specific intervals and in specific patterns across
          the Earth when we are closest to a nearby star
    B) Night-by-night photography of nearby stars at hydrogen Balmer wavelengths
    C) Continuous radio and microwave listening and transmitting at frequencies at
          which the natural radio sky noise background is low
    D) X-ray surveys of space at appropriate times (e.g., when Earth is closest to nearby
          stars in its orbit), in view of the penetrability of space at these wavelengths
    Ans: C
    Section: 19-3




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31. What conditions restrict the suitable wavelength range for communication with
    extraterrestrial intelligence to the “water hole” in the high-frequency radio range of the
    electromagnetic spectrum (see Fig. 19-5 of Kaufmann and Comins, Discovering the
    Universe, 7th Ed.)?
    A) Cosmic background radio noise at low frequencies and radio noise from the Sun
          and Jupiter at high frequencies
    B) Local radio noise from TV, radio, and aircraft across the band, except a narrow
          range in which transmission is prohibited by international agreement in order to
          permit such extraterrestrial communication
    C) Atmospheric absorption by the ionosphere at low frequencies and by CO2 at high
          frequencies in the long infrared range
    D) High galactic radio background noise at low frequencies and high atmospheric
          absorption by H2O and O2 at high frequencies, with a suitable region in between
    Ans: D
    Section: 19-3

32. Why would intelligent alien beings wanting to communicate with us probably choose
    the 21-cm atomic hydrogen radio wavelength?
    A) Because this wavelength shows a very strong Doppler effect when its source is
          moving, and they would know that we would be able to detect the orbital motion
          of their home planet around their star by this method
    B) Because they would expect that many of our telescopes would already be tuned to
          this precise wavelength for scientific work
    C) Because this radiation at this particular wavelength is very weak from natural
          sources in space and messages would be easily distinguished from other sources
    D) Because they would have detected this particular wavelength from our
          transmitters on the Earth since it is used extensively for satellite communications,
          and they would know that we could detect them easily
    Ans: B
    Section: 19-3

33. What is the current state of the search for extraterrestrial radio communications?
    A) Several extraterrestrial civilizations have been found, but they are not intelligent
          enough for us to bother with and the search is continuing.
    B) Occasional single-frequency searches have been made for extraterrestrial signals,
          but funds are still being sought for the first major continuous monitoring effort.
    C) A number of frequencies in the “water hole” are being monitored, but there has
          been no major effort as yet to send out continuous signals from the Earth at these
          frequencies.
    D) Continuous transmissions are being sent out from the Earth at several frequencies
          in the “water hole,” and tens of millions of other frequencies are being monitored.
    Ans: C
    Section: 19-3




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34. One of the first people to look for radio signals from extraterrestrial civilizations was
    A) Arno Penzias.                               C) Jocelyn Bell.
    B) Frank Drake.                                D) Martin Schwarzschild.
    Ans: B
    Section: 19-3

35. The earliest searches for radio signals from extraterrestrial civilizations were made
    about
    A) 1973.       B) 1960.      C) 1995.       D) 1948.
    Ans: B
    Section: 19-3

36. The first successful detection of signals from extraterrestrial civilizations was
    accomplished in which year?
    A) 1985
    B) Never—no such signals have been detected yet.
    C) 1999
    D) 1960
    Ans: B
    Section: 19-3

37. The so-called “water hole” is a range in the electromagnetic spectrum in which searches
    for transmissions of extra-terrestrial origin are being conducted. In what region of the
    electromagnetic spectrum does the “water hole” occur?
    A) Ultraviolet      B) Visible       C) Infrared       D) Microwave
    Ans: D
    Section: 19-3

38. In searching for transmissions from intelligent civilizations, SETI is concentrating its
    efforts on a survey of
    A) about a dozen or so of the closest stars.
    B) just those stars around which we believe we have detected planets.
    C) thousands of stars within a 100 pc or so of the solar system.
    D) stars in giant elliptical galaxies since these, being oldest, are most likely to have
           advanced civilizations.
    Ans: C
    Section: 19-3




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39. If we are going to “listen” for electromagnetic radiation at 21 cm from extraterrestrial
    sources, then we had better not generate too many waves at this wavelength from
    terrestrial sources. The standard FM broadcast band (as you can see by looking at your
    radio dial) spans frequencies from 88 MHz (million cycles per second) to 108 MHz.
    How does the frequency of the 21-cm signal compare with the FM band? The
    frequency of the 21-cm line is
    A) below the low frequency end of the FM band by a factor of about 9.
    B) right in the middle of the FM band.
    C) right at the upper end of the FM band.
    D) higher than the top end of the FM band by a factor of about 13.
    Ans: D
    Section: 19-3

40. The Drake equation attempts to predict
    A) the number of inhabitable planets around stars in our Galaxy.
    B) the number of intelligent civilizations that exist in the whole universe.
    C) the probability of primitive life existing elsewhere in our Galaxy.
    D) the number of technically advanced civilizations in our Galaxy.
    Ans: D
    Section: 19-4

41. The numerical value given by the Drake Equation
    A) is exactly 10.
    B) is generally agreed to be around 10, certainly between 8 and 12.
    C) could be almost any value from zero on up to 1 billion.
    D) has a lower limit of 1 but could be much larger than 10.
    Ans: D
    Section: 19-4

42. In what way does the Drake equation combine the various factors (e.g., fraction of stars
    with planets, fraction of planets that can support life, etc.) in an attempt to determine the
    number of technically advanced civilizations existing elsewhere in our Galaxy?
    A) The product of all the probabilities is calculated.
    B) The sum of each of the factors is determined.
    C) The sum of three factors is divided by the sum of the other four factors.
    D) The sum of the last six factors is subtracted from the initial factor, the rate of
          solar-type star formation.
    Ans: A
    Section: 19-4




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43. In the Drake equation for estimating the possible number of technically advanced
    civilizations in our Galaxy, the factor for the rate at which solar-type stars form in a
    galaxy excludes massive stars with masses greater than about 1.5 times that of the Sun.
    Why?
    A) Such stars have much shorter lifetimes than it took for intelligent life to develop
           on the Earth and hence should probably not be considered.
    B) Such stars never develop a nuclear furnace in their interiors and hence can never
           heat any planet sufficiently to sustain life.
    C) These stars would never develop nuclear processes that could produce heavy
           elements (e.g., iron) needed for planetary formation.
    D) Such stars are prone to repeated and violent supernova explosions throughout
           their lives, which would destroy any developing life-forms.
    Ans: A
    Section: 19-4

44. Probably the most difficult factor to estimate in the Drake Equation is
    A) R*, the rate at which solar-type stars form in the Galaxy.
    B) fp, the fraction of stars that have planets.
    C) ne, the number of planets per solar system that are Earthlike (suitable for life).
    D) L, the lifetime of a technologically advanced civilization.
    Ans: D
    Section: 19-4

45. For which of the following factors in the Drake Equation do we actually have
    observational knowledge rather than just a speculative estimate?
    A) R*, the rate at which solar-type stars form in the Galaxy
    B) fl, the fraction of Earthlike planets on which life actually arises
    C) fi, the fraction of life-forms that evolve into intelligent species
    D) fc, the fraction of intelligent species that develop adequate technology and then
          choose to send messages out into space
    Ans: A
    Section: 19-4

46. Around which types of stars are we most likely to find planets supporting our kind of
    life?
    A) High-mass main-sequence stars            C) Very-low-mass stars
    B) Red giant stars                          D) Low-mass main-sequence stars
    Ans: D
    Section: 19-4




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47. It is unlikely that planets near stars much more massive than our Sun would develop life
    because
    A) planets would have to be too close to these cool stars in order to be sufficiently
           warm for life to evolve and they would become tidally linked, resulting in no
           night and day.
    B) these stars would have evolved to red giant and even supernova stages before life
           could evolve sufficiently to produce a civilization.
    C) no Moon would form around a planet near such a star, and a Moon is considered
           to have been essential for the evolution of life because of tidal variations on the
           Earth.
    D) there would be no region around the star where UV, visible, and IR light
           intensities would be suitable for the evolution of life.
    Ans: B
    Section: 19-4

48. Why do we only consider stars with masses less than about 1.5 solar masses in the
    Drake equation when estimating the number of possible stars in our Galaxy around
    which planets could form that would support our kind of intelligent life?
    A) Massive stars would produce massive planets on which life would not be possible.
    B) Such massive stars would never reach temperatures sufficient to maintain
          life-supporting conditions on the surfaces of its planets.
    C) A more massive star would produce so much damaging UV radiation that it would
          sterilize its planets.
    D) Stars more massive than this would have evolved so rapidly that an advanced
          civilization would not have had time to evolve and develop.
    Ans: D
    Section: 19-4

49. It is unlikely that intelligent life would develop on a planet circling a star of
    significantly less mass than the Sun because
    A) no Moon would form around a planet near such a star, and a Moon is considered
           to have been essential for the evolution of life because of tidal variations on the
           Earth.
    B) the lifetime of such a star on the main sequence is too short; life-forms on such a
           planet would not have time to evolve intelligence.
    C) the planet would likely become tidally locked to the star, making one side of the
           planet too hot and the other side too cold.
    D) there would be no region around the star where UV, visible, and IR light
           intensities would be suitable for the evolution of life.
    Ans: C
    Section: 19-4




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50. How often do Sunlike stars (of a type considered likely to be circled by an inhabitable
    planet) form in our Galaxy, on average?
    A) Hundreds of such stars form per year
    B) About one such star forms per year
    C) We cannot yet answer this question
    D) Less than one such star forms per thousand years
    Ans: B
    Section: 19-4

51. One of the important numbers in determining how many extraterrestrial civilizations
    there may be at the present time in our Galaxy is the following: Out of those stars that
    have planets, what fraction, fs, of those stars have planets suitable for life? (This is
    similar to the number ne in the Drake equation.) Based on the extrasolar planets already
    found by astronomers (see Sections 5-6 and 5-7 of Kaufmann and Comins, Discovering
    the Universe, 7th Ed.), what is a good guess for fs? (Note: If all stars with planets have
    at least one planet suitable for life, then fs = 1; if no such star anywhere in the Galaxy
    has a planet suitable for life, then fs = 0.)
    A) fs = 0 since no star has yet been found to have an inhabitable planet
    B) Close to fs = 1 since most stars so far found to have planets have high-mass
           planets (similar to Jupiter or larger) orbiting far from the star, indicating that our
           solar system is probably typical of planetary systems in general
    C) Close to fs = 1/2 since about half of the stars so far found to have planets have
           planets similar in mass to the Earth orbiting the star at about the Earth's distance
           from the Sun
    D) fs less than about 1/10 since most stars so far found to have planets have
           high-mass planets (similar to Jupiter or larger) orbiting close to the star, which
           would disrupt the orbit of an inhabitable planet
    Ans: D
    Section: 5-6, 5-7 and 19-4

52. In a few decades, a new generation of powerful telescopes especially designed to find
    extrasolar planets may be operational and sending us data. What might these results
    mean for our use of the Drake Equation?
    A) With these results in hand, the Drake Equation will become irrelevant.
    B) The structure of the Drake Equation itself will undoubtedly have to be drastically
           revised.
    C) We will have much better values for the factors fp (the fraction of stars that have
           planets) and ne (the number of planets per solar system that are Earthlike).
    D) We will have much better values for the factors fl (the fraction of Earthlike planets
           on which life actually arises), fi (the fraction of life-forms that evolve into
           intelligent species), and fc (the fraction of intelligent species that develop adequate
           technology and then choose to send messages out into space).
    Ans: C
    Section: 19-4




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53. Which of the following events of the past century do you think will have announced our
    presence on the Earth most effectively to extraterrestrial watchers?
    A) The appearance of artificial satellites orbiting the Earth after 1957
    B) Nuclear weapons explosions producing extremely intense but brief flashes of light
          and electromagnetic radiation
    C) Slow changes in vegetation patterns and the appearance of manmade structures
          such as road systems and cities on the Earth
    D) The slow build-up of radio transmissions after the invention of radio, with
          modulated signals carrying sound and visual television images
    Ans: D
    Section: 19-5

54. If we do eventually make contact with other civilizations across space, which of the
    following conditions will inevitably hold?
    A) We will not be able to understand the messages.
    B) The civilization is likely to be very much more primitive than ours in terms of
          technology.
    C) Conversations will take a very long time.
    D) The chemistry and biology of the life-forms are likely to be very different from
          ours—for example, silicon-based rather than carbon-based.
    Ans: C
    Section: Chapter 19




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