Deck 27: The Search for Extraterrestrial Life

Question 1

Silicon has often been suggested as an alternative to carbon in biochemistry. Each of the following is one reason silicon is unsuitable for such a role EXCEPT ONE. Which is the EXCEPTION?

A)Silicon compounds are too soft or too hard to be part of living organisms.
B)Silicon compounds react too much or too little to be part of living organisms.
C)Silicon atoms bond with up to four other atoms.
D)Silicon compounds react too slowly to undergo the rapid changes required of molecules in organisms.

Answer 1

C

Question 2

Several lines of evidence now suggest that large and complex organic molecules, from which the building blocks of life could be formed, have evolved in outer space. Which of the following is NOT one of these observational findings?

A)the discovery of large organic molecules on and under the soils of Mars and the Moon
B)laboratory experiments in which electrical sparks passing through a combination of simple gases such as H₂O, H₂, N₂, and CO₂ produced large organic molecules
C)radio astronomical observations of large organic molecules in giant molecular clouds
D)the discovery of organic molecules inside certain meteorites that arrived upon Earth

Answer 2

A

Question 3

Organic compounds have been found in each of the following EXCEPT ONE. Which is the EXCEPTION?

A)meteorites
B)comet spectra
C)interplanetary dust
D)spectra of asteroids

Answer 3

D

Question 4

In which of the following environments have long-chain carbon-based molecules not been found?

A)in interstellar gas clouds
B)on the surface of Earth
C)inside meteorites
D)on the surfaces of nearby planets such as Venus and Mars

Question 5

What are amino acids?

A)the simplest living organisms
B)substances found in Earth's atmosphere, and perhaps on other bodies as well, which attack simple life-forms
C)carbon compounds considered key to life because they are found only in very primitive life-forms
D)the building blocks of proteins, the foundation of Earth-based life

Question 6

The method used in the Urey-Miller experiment was to:

A)pass an electric arc through a mixture of hydrogen, ammonia, methane, and water and then look for organic compounds.
B)send radio signals using a pulsed code toward nearby Sun-like stars that may have planets.
C)attach a metal plaque to the Voyager spacecraft to tell extraterrestrial beings about us, if they ever find the spacecraft.
D)monitor tens of millions of frequencies at once in an effort to detect extraterrestrial radio communications.

Question 7

In what way was volcanism important to the development of life on Earth?

A)Volcanoes provided the heat necessary for the chemical reactions to create complex organic molecules.
B)Amino acids were probably present in the gases emitted.
C)Carbon dioxide, water vapor, and nitrogen were outgassed from volcanoes.
D)Molten lava dissolved various organic materials on Earth's surface and allowed them to mix together so they could react.

Question 8

Which one of Saturn's satellites has been suggested as the site of a subsurface liquid water ocean?

A)Enceladus
B)Iapetus
C)Pandora
D)Rhea

Question 9

In both the labeled-release and pyrolytic-release experiments conducted on Mars by the Viking Landers, carbon compounds were fed into the system and then this carbon was searched for after being potentially involved in respiration or photosynthesis. But how would we know it was the SAME carbon atoms?

A)Atoms produced on Earth are distinct from those produced elsewhere in the universe.
B)Carbon is not part of the Martian composition, so any carbon detected would have to be part of the original sample.
C)The released carbon was a radioactive isotope and was thus easily traceable.
D)What was done was to measure the total volume of carbon in the sample. Any increase in this volume would indicate that the sample had stimulated the production of additional carbon.

Question 10

What process or observation misled scientists into believing initially that their life-seeking experiments on the Mars Viking Lander had succeeded in detecting evidence of life on our neighboring planet?

A)reaction of water with unstable chemicals that exist upon the surface of Mars
B)growth of substances when water was added, which later turned out to be crystal growth from inert chemicals
C)motions of microscopic components, looking like those of a life-form, but which were caused by the boiling of water under the artificial sunlight of the experiment
D)extremely high absorptivity of Martian rocks to water, because these rocks mimicked life-forms by absorbing water

Question 11

One proposed test for determining life on Mars is to measure carbon isotopes in rock samples. How could this indicate life?

A)Biological organisms preferentially concentrate ¹²C and not ¹³C.
B)Biological organisms preferentially concentrate ¹³C and not ¹²C.
C)Radiogenic¹⁴C dating can be used to determine when an organism ceased to take in carbon from the atmosphere.
D)A carbon compound, benzene (C₆H₆), is produced by biological organisms on Earth. A detection of benzene on Mars should indicate life.

Question 12

Which of the following has placed Martian rocks in the hands of scientists on Earth?

A)materials recovered from a spacecraft that landed near to Roswell, New Mexico, but that were never released to the general public
B)a sample-return mission by the former USSR space exploration program
C)rocks returned by astronauts from the Moon, whose Martian origin was established by their chemical makeup and red color
D)meteorites collected from Antarctica, the gases within them indicating that they have been blasted from Mars by an impact

Question 13

Why do we believe that some meteorites, such as the Antarctic find ALH 84001, originated on Mars?

A)The color matched the red of the Martian soil.
B)Each of these meteorites landed in soft soil or snow in such a manner that the landing trajectory could be determined.
C)The ALH 84001 meteorite was actually tracked by radar on the final part of its inbound journey.
D)The air trapped in pockets in the meteorites matched the Martian atmosphere but was very different from Earth's atmosphere.

Question 14

Some meteorites found on Earth are believed to come from Mars because trapped bits of atmosphere in these meteorites match the composition of Mars's atmosphere. What more can be said about this?

A)The comparison to Mars's atmosphere is to recent samples taken by the Viking Landers. However, this is not a problem because Mars's atmosphere has been stable for a long time.
B)The atmospheric samples in the meteorites contained much water vapor, further evidence of a wet period in Mars's past.
C)The atmospheric samples in the meteorites are very different from the samples gathered by the Viking Landers of the present composition of Mars's atmosphere. But the meteorites are believed to contain samples of an ancient Martian atmosphere.
D)Some of the meteoritic rocks have also been traced to specific craters on Mars.

Question 15

We believe the meteorite ALH 84001 came from Mars because of trace amounts of gas trapped in the rock. What does analysis of this gas reveal?

A)The gas matches the carbon dioxide-nitrogen composition of Mars's very early atmosphere some 4.5 billion years ago. This is also the age given by radioactive dating of this meteorite.
B)The gas contains a combination of water vapor, iron oxide, and carbon dioxide, which we believe are unique to the surface of Mars in its "wet" period 4.5 billion years ago.
C)The gas matched the current composition of the Martian atmosphere measured by the Viking Landers. This would also be the composition when the rock was blasted off the surface 16 million years ago. Presumably, this blast would have melted the rock and trapped some gas inside.
D)In addition to a composition that matches the atmosphere of Mars, the gas contains the right amount of space dust to be consistent with orbiting the Sun for 16 million years.

Question 16

The meteorite Nakhla is one of several meteorites believed to originate on Mars, which show small tunnel structures similar to Earth rocks inhabited by rock-eating microbes. But Nakhla is special for another reason. What is that reason?

A)It was the first meteorite to exhibit such tunnels.
B)The rock's composition has been traced to a specific crater on Mars.
C)The fall of this meteorite was observed, so it could not have been contaminated by being on Earth for a long period.
D)It is a carbonaceous chondrite, and as such contains carbon compounds and volatile materials as a result of never having been heated.

Question 17

Why do we only consider stars with masses less than about 1.5 M_e 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)This type of star would produce so much damaging UV radiation that it would sterilize its planets.
B)Such massive stars would never reach temperatures sufficient to maintain life-supporting conditions on the surfaces of its planets.
C)Stars more massive than this would have evolved so rapidly that a sufficiently advanced civilization would not have had time to evolve and develop.
D)Planets could not form sufficiently close to such stars for life to have survived and evolved.

Question 18

The Drake equation calculates the number of technically advanced civilizations in the galaxy as a product of seven factors: R_*, f_p, n_e, f_l, f_i, f_c, and L. In the sample calculation in the text, these values are taken as 1 × 1 × 0.1 × 1 × 1 × 1 × 100 = 10. If we were to redo the calculation, increasing each increasable factor by a multiple of 10, what would our result be?

A)10
B)10⁴
C)10⁶
D)10⁸

Question 19

If we were able to detect radio signals from an intelligent civilization, we would hope they are doing all of the following things, EXCEPT ONE. What is the EXCEPTION?

A)sweeping the skies with a focused beam of radio waves
B)using a broadband of radiation to target more receivers
C)using a frequency near the "water hole"
D)using a repeating signal unlike a natural source like a pulsar

Question 20

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)Several private or university-based searches using existing telescopes and links to millions of private home computers are searching at many frequencies.
C)Continuous transmissions are being sent out from Earth at several frequencies in the "water hole," and tens of millions of other frequencies are being monitored.
D)Several dedicated telescopes are continuously monitoring the neighborhoods of nearby stars, which are known to have planets, for bright flashes or coded signals at common visible laser wavelengths.

Question 21

What is the Allen Telescope Array?

A)a large radio telescope array in Texas, which will concentrate on watching for signals from a single nearby star over time
B)a large radio telescope array designed to work in tandem with the Kepler spacecraft, which is observing nearby stars for planetary systems
C)a large radio telescope array that will concentrate on 100,000 nearby solar-type stars
D)a series of a dozen radio telescopes placed in orbit where they are more effective at receiving radio signals

Question 22

Since the wobble that we have used to detect Jupiter-sized planets around other stars would be extremely small for an Earth-sized planet, we plan to use several other techniques to find and analyze Earth-sized planets in the near future. These include all but one of the following. Which one is the EXCEPTION?

A)transits
B)detection of infrared radiation
C)searching for objects with high albedos, indicating the presence of water or ice
D)analysis of atmospheric spectra

Question 23

Which molecules, whose absorption lines appear in the infrared, are considered most likely to indicate the presence of life if they were detected on any planet orbiting another star?

A)hydrogen and helium
B)methane and ammonia
C)carbon dioxide
D)carbon dioxide, ozone, and water vapor

Question 24

In a few decades, orbiting telescopes such as Kepler and James Webb Space Telescope (JWST) may be operational and sending us data. What might these results mean for our use of the Drake equation?

A)mirrors whose shapes are precisely determined by laser-computer mechanisms
B)active optics
C)adaptive optics
D)interferometry

Question 25

In looking for exoplanets, one important discovery target is oxygen because:

A)oxygen was an important component of the original solar nebula, and the solar system could not have formed without it.
B)oxygen is an important part of water, one of the most important ingredients in Earth-based life.
C)oxygen's spectrum is part of the infrared spectrum where planets are brighter and stars are dimmer.
D)Earth's atmospheric oxygen was produced by living organisms, and we are unaware of any nonbiological method for producing an oxygen atmosphere.

Question 26

A key target in our radio telescope search for exoplanets harboring life is:

A)ozone because it is produced from oxygen and easy to detect in the infrared part of the spectrum.
B)silicon because it is one of the most abundant elements on Earth and also a possible candidate as a base for biological molecules.
C)carbon because our life-forms are based on carbon.
D)iron because advanced civilizations are hard to imagine without it.