The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 19 Life in the Universe
19.1 Multiple Choice Questions
1) How do scientists study the history of life on Earth?
A) by assuming that life in the past was just like present-day life
B) by comparing present-day organisms with each other, and assuming past life had mixed traits
of present-day organisms
C) by using telescopes to look far away, and thus see what life was like in the past
D) by studying fossils, the preserved remains of past organisms
2) How do scientists determine the age of fossils?
A) They only determine relative ages by assuming that deeper layers of sedimentary rock are
older.
B) They use radiometric dating to measure the age of the surrounding rocks.
C) They compare the ratio of carbon-12 to carbon-13 in the fossil to determine how long ago it
formed.
D) They basically guess since there are too many unknown variables to determine fossil ages.
3) Why are relatively few details known about the life that existed on Earth prior to a few
hundred million years ago?
A) Nearly all life at that time was microscopic, making it much more difficult to identify.
B) Older rocks are more rare than younger rocks because of geologic processes like subduction.
C) Many rocks have been transformed by high heat and pressure, destroying any fossils they
contained.
D) all of the above
4) What evidence suggests that life was present on Earth within a billion years of its formation?
A) Life must have formed early in order to produce the variety of lifeforms seen today.
B) Fossils have been found in rocks that are over 4 billion years old.
C) Some stromatolites have been found that are 3.5 billion years old.
D) The chemical composition of rocks known to be 3.5 billion years old shows that oxygen
levels in the atmosphere indicate the presence of plant life.
5) The figure above shows the geological times scale. Animals have been present on land for
approximately ________ of the Earth’s history.
A) 1/10
B) 1/5
C) 1/2
D) 3/4
6) The figure above shows the geological times scale. The Earth’s atmosphere has been oxygen
rich for
A) a few million years.
B) about 500 million years.
C) about 2 billion years.
D) its entire history.
7) The figure above shows the geological times scale. Life has existed for ________ of the
Earth’s history.
A) all
B) about 85%
C) about 50%
D) about 25%
8) The figure above shows the geological times scale. Mammals have been prominent for
approximately ________ of the Earth’s history.
A) 0.15%
B) 1.5%
C) 15%
D) 50%
9) The figure above shows the geological times scale. The K-T event that marks the boundary
between when dinosaurs were prominent and mammals became prominent occurred
approximately _______ years ago.
A) 65 million
B) 10 million
C) 650 million
D) 100 million
10) What evidence suggests that life arises relatively easily?
A) Small animals like Tardigrades can survive exposure to the near-vacuum of space.
B) Life is currently present in extreme environments like deep ocean volcanic vents.
C) Life was present on Earth soon after the end of the heavy bombardment period.
D) All organisms on Earth use DNA as their genetic material.
11) Which process(es) contribute(s) to the gradual evolution of life via natural selection?
A) Organisms tend to produce more offspring than the local environment can support.
B) Individuals in a population vary in many heritable traits.
C) The competition for resources will favor those individuals in a population with traits that
make them more competitive.
D) all of the above
12) Why do scientists suspect that life first arose near deep-sea volcanic vents or similar
environments with abundant chemical energy?
A) A deep ocean environment would have protected early organisms from ultraviolet radiation
before the formation of the ozone layer.
B) All organisms have similar DNA, with further relations having greater differences.
C) Deep-sea volcanic vents would have been the only source of energy present on Earth when
life was forming.
D) all of the above
13) Which observation(s) and/or experiment(s) demonstrate ways that the chemical building
blocks of life (amino acids and DNA bases) could have originated on the early Earth?
A) These complex molecules have been found within meteorites.
B) Experiments have shown that naturally occurring clays can catalyze the formation of RNA
strands.
C) Amino acids and DNA bases form from simple chemical reactions in experiments simulating
the early Earth atmosphere.
D) all of the above
14) What are scientists’ best guess(es) for the requirement(s) of life?
A) energy to fuel the activities of life
B) liquid water
C) a source of materials (nutrients)
D) all of the above
15) Where have scientists begun an active search for life beyond the Earth?
A) the Moon
B) Venus
C) Mars
D) Europa
E) Titan
16) The only place outside of Earth for which there is irrefutable evidence for ancient, microbial
life is
A) the Moon.
B) Mars.
C) Europa.
D) Titan.
E) None of the above—there is no irrefutable evidence for life beyond Earth.
17) Martian meteorites have been found on Earth. How do we know these meteorites came from
Mars?
A) Their chemical composition matches that of known Martian rocks.
B) Their ages match the known age of Mars.
C) Their color is the same as most Martian rocks.
D) Their composition tells us they formed farther from the Sun than Earth.
18) After Mars, the next most likely candidates for life in the solar system are
A) comets in the Oort cloud.
B) the atmospheres of the Jovian planets.
C) the large moons of the Jovian planets.
D) the largest asteroids.
E) comets in the Kuiper-belt.
19) Which of the following are the best candidates to search for planets that might harbor
extraterrestrial life?
A) halo stars, because planets can form in isolation from disruptive stellar encounters
B) low mass stars (less than one-tenth of the mass of the Sun), because these are the most
common stars in our galaxy
C) massive stars (greater than twice the mass of the Sun), because they provide more energy to
promote biology
D) solar-mass stars, because they have both a large habitable zone and a long stellar lifetime.
E) binary stars, because they provide twice as much energy to promote biology
20) How would it be possible for a large moon of a jovian-size planet to support life on its
surface?
A) The moon must be locked in synchronous rotation with its planet.
B) The jovian planet would need to migrate inward towards its star until it was in the habitable
zone.
C) The moon would need to have a magnetic field.
D) The moon would need to have plate tectonics.
E) The moon would need to have a high density.
21) Which of the following gases, which we can detect (if present) in infrared spectra, would be
a strong indicator of life on another planet?
A) carbon dioxide
B) ozone
C) nitrogen
D) water vapor
E) sulfuric acid
22) Mars is just barely in the habitable zone of the Sun. Why is Mars not currently habitable?
A) It is too hot for water to exist as a liquid on its surface.
B) It does not have the necessary energy source life needs.
C) It is too cold for water to exist as a liquid on its surface.
D) It is bombarded too often with asteroids and comets.
E) It has too little gravity for water to exist as a liquid on its surface.
23) Which of the following was the most important for maintaining the Earth’s stable climate
over the time it took for large organisms to evolve?
A) bombardment by water bearing planetesimals
B) the cessation of the heavy bombardment phase
C) plate tectonics
D) the tides
E) underground sea vents
24) Why is a global magnetic field thought to be necessary for life to exist on the surface of
planet?
A) A magnetic field shields the planet from harmful ultraviolet light.
B) A magnetic field helps form ozone in the upper atmosphere.
C) A magnetic field helps keep the planet’s atmosphere from being stripped away by stellar
winds.
D) A magnetic field helps warm the planet’s surface through the greenhouse effect.
25) What defines the habitable zone around a star?
A) the region around a star where rocky planets can form
B) the region around a star where humans can survive
C) the region around a star where liquid water can exist on planetary surfaces
D) the region around a star where its ultraviolet radiation is too weak to destroy biological
organisms on a planetary surface
E) the region around a star outside of its hot, tenuous corona
26) Which of the following statements best reflects our current knowledge about the term flife in
the equation
Number of Civilizations = NHP × flife × fcivilization × fnow?
A) The value of flife is either 0 or 1.
B) The value of flife is between 0 and 1.
C) The value of flife is less than 0.0000001.
D) The value of flife is equal to 1/2.
E) The value of flife is greater than 10.
27) At present, what is the primary way that astronomers carry out SETI programs (that is,
search for extraterrestrial intelligence)?
A) by searching for planets around distant stars
B) by using X-ray telescopes to search for signals from extraterrestrial civilizations
C) by using radio telescopes to search for signals from extraterrestrial civilizations
D) by analyzing high-resolution images of nearby stars in search of artificial structures
E) by analyzing the spectra of extra-solar planets in an attempt to detect oxygen
28) In 1974, a radio message was sent out from the Arecibo observatory in Puerto Rico towards a
globular cluster, 25,000 light-years away. Approximately how far has this message gotten as of
today?
A) It’s just beyond the Neptune in our solar system.
B) It’s just passing through the Oort cloud surrounding our solar system.
C) It’s just passing stars that are close neighbors to the Sun in the Milky Way.
D) It’s almost at the center of the Milky Way.
E) It’s already arrived at the globular cluster.
29) SETI (the Search for Extraterrestrial Intelligence) searches for electromagnetic signals from
life on planets or moons
A) within the solar system.
B) around nearby stars.
C) in globular clusters.
D) toward the center of the Milky Way.
E) in other galaxies.
30) At about what fraction of the speed of light do our fastest spacecraft travel?
A) 1/2
B) 1/10
C) 1/100
D) 1/1,000
E) 1/10,000
31) The Voyager I and II spacecraft visited the Jovian planets in the 1980s. When will they reach
the distances of the nearest stars?
A) in our lifetime
B) in our children’s lifetime
C) in our grandchildren’s lifetime
D) thousands of years from now
E) about 100,000 years from now
32) Which of the following describes a major challenge of interstellar travel at near light speed?
A) Any interstellar journey will take much longer than the lives of the crew members.
B) Time dilation will slow the heartbeats of the crew to a dangerously low rate.
C) Atoms and ions in interstellar space will hit the spacecraft like a flood of dangerous cosmic
rays.
D) Asteroid fields floating in interstellar space will present a severe navigational challenge.
E) Supernova explosions could destroy spaceships passing nearby.
33) Which of the following statements about matter-antimatter engines is not true?
A) Matter-antimatter reactions represent the most efficient reactions possible in terms of energy
release.
B) Matter-antimatter engines would be possible in theory, but to date, we have no evidence that
antimatter exists.
C) One of the major challenges to developing matter-antimatter engines is finding a way to
produce enough antimatter.
D) One of the major challenges to developing matter-antimatter engines is finding a way to store
antimatter after it is produced.
E) Spacecraft powered by matter-antimatter engines could probably reach speeds of 90 percent
of the speed of light.
34) Which of the following best explains why an interstellar ramjet could, in theory, achieve
continuous acceleration?
A) It uses fuel that is more efficient than any other known fuel.
B) It collects its fuel as it goes, rather than having to carry the weight of fuel along with it.
C) It takes advantage of theoretically possible loopholes in Einstein’s theory of relativity.
D) It has such a large fuel tank that it will essentially never use up all the fuel it carries.
E) Its speed always gets faster because time dilation changes the rate at which time flows.
35) Which of the following is not a possible solution to the Fermi Paradox?
A) We are the only intelligent civilization to have ever arisen in the Milky Way.
B) Of all of the intelligent civilizations in the Milky Way, none has chosen to create a galactic
civilization.
C) There is a galactic civilization, but we are currently unable to detect or recognize it.
D) There is a galactic civilization, but it is being actively hidden from us.
E) Given the current age of our galaxy, there has not been enough time for a galactic civilization
to develop.
36) What is the Fermi Paradox?
A) Galactic civilizations seem forbidden by the laws of physics.
B) Interstellar travel is possible yet would take an infinite amount of time because of relativistic
time-dilation.
C) We would be unable to detect an Earth-like planet even at a distance of a few light-years.
D) Reasonable assumptions predict that a galactic civilization should have already arisen in the
Milky Way, yet we have absolutely no evidence for it.
E) The Drake equation predicts that there should be no intelligent life in the Milky Way, yet we
exist.
19.2 True/False Questions
1) There is good evidence that life on Earth was thriving 3.5 billion years ago.
2) The modern-day organisms that seem oldest, in an evolutionary sense, are microbes that
live in the hot water around volcanic vents on the ocean floor.
3) Nearly all of the oxygen in the Earth’s atmosphere was originally produced by photosynthesis
in the leaves of trees that covered the continents 3.5 billion years ago.
4) The requirement of liquid water is the most severe constraint on the development of life.
5) The habitable zone around a star refers to the places where living organisms are found.
6) We have already launched spacecraft whose orbits will carry into interstellar space.
7) The Pioneer and Voyager spacecraft carry a message from Earth, just in case an alien
civilization ever runs across them.
8) We have already launched a spacecraft bound for Alpha Centauri.
9) One idea for interstellar spacecraft involves harnessing energy from nuclear bombs detonated
in space.
10) Relativistic time-dilation means that astronauts aboard a spaceship traveling close to the
speed of light will actually age less than their families left behind on the Earth.
11) Although antimatter is an interesting theoretical idea, there is no evidence that it actually
exists.
12) If they existed, and if they were watching, a civilization at the center of the Milky Way could
have detected our first TV signals by now.
19.3 Process of Science Questions
1) Evolution as a Scientific Theory: Detractors often dismiss evolution by emphasizing the role
randomness plays in the theory. They argue that a living creature (such as a human being) is
about as likely to have evolved by random chance as a Boeing 747 airplane is of being
assembled by a tornado flying through a junkyard. Explain why this vivid analogy is
nevertheless fundamentally flawed by correctly explaining the role that randomness plays in the
theory of evolution.
2) Generalizing from a Single Example: Many would argue that our concept of life and
intelligence is severely limited by the fact that we have only the “single example” of the Earth.
Do you agree with this view (address the questions of life and intelligence separately)? To what
extent do you feel that the search for extraterrestrial life is biased by the example of life on the
Earth? Does the search for extraterrestrial intelligent life suffer more or less from the same bias?
3) Science Fiction as a Driver of Science? This chapter, more than any other in the book,
involves familiar themes of science fiction: space travel, extraterrestrial life, extraterrestrial
intelligence, and more. Give and discuss two concepts that started out as science fiction but
ended up as science fact. Give and discuss an example of an idea from science fiction that will
likely never be realized as science fact. Do you think that the rise in popularity of science fiction
(Star Trek, Star Wars, and others) has increased or decreased the general public’s understanding
of science? Explain.
19.4 Short Answer Questions
1) What is the evidence that suggests planetary systems are common in the universe?
2) Why do we rule out stars with masses more than a few times that of the sun when we consider
star systems where life could be possible?
3) Why might so-called super-Earth planets have been able to support life at a greater distance
from their star than an Earth-sized planet?
4) If we detected an Earth-like planet in the habitable zone around another star, how might we
learn whether it harbored life?
5) Briefly explain the meaning of each term in the equation
Number of Civilizations = NHP × flife × fcivilization × fnow.
6) Briefly explain the purpose of the equation
Number of Civilizations = NHP × flife × fcivilization × fnow.
7) Briefly summarize current knowledge about the term NHP in the equation
Number of Civilizations = NHP × flife × fcivilization × fnow.
8) Briefly summarize current knowledge about the term flife in the equation
Number of Civilizations = NHP × flife × fcivilization × fnow.
9) Why do we need new forms of technology to make it possible to journey to the nearest stars
within a human lifetime?
10) Briefly explain the Fermi Paradox, namely the paradox of the question “Where are the
aliens?”
19.5 Mastering Astronomy Reading Quiz
1) According to fossil evidence, how far back in time did life on Earth exist?
A) about 3.5 billion years or more
B) about 2.0 billion years
C) about 65 million years
D) about 545 million years
2) Why do scientists say that evolution is a “theory”?
A) because it explains a great deal about life and is supported by an enormous body of evidence
B) because it’s really just a guess about how life developed on Earth
C) because they are not very confident that it really happens
D) because it has yet to be tested in any meaningful way
3) What is a mutation?
A) a change in a living cell’s DNA
B) a change in the type of food an organism consumes
C) a change in the physical appearance of a living organism
D) a change in an organism that turns it into a different species
4) Based on DNA studies, it seems that all life on Earth ________.
A) shares a common ancestor
B) requires oxygen to survive
C) arose from one of five distinct ancestors that lived about two billion years ago
D) belongs to one of just two kingdoms: plants and animals
5) Which of the following is considered by biologists to be a likely place where life might have
first arisen on Earth?
A) deep in Earth’s core
B) in hot water near undersea volcanoes
C) on meteorites that landed on Earth
D) on land surfaces that got moderately heavy rainfall
6) How did oxygen (O2) get into Earth’s atmosphere?
A) It was outgassed from volcanoes.
B) It came from chemical reactions with surface rocks.
C) It was released by life through the process of photosynthesis.
D) It was captured from the solar nebula.
7) Why is it likely that animals were unable to colonize the land until about 400 million years
ago?
A) Major impacts were occurring up until this time, which would have wiped out any life on
land.
B) Ozone in our atmosphere did not exist in sufficient levels to block UV light prior to this time.
C) Earth’s surface was molten prior to this time.
D) Oceans covered the entire surface of Earth prior to this time.
8) Which of the following best describes what we mean by a habitable world?
A) a planet or moon that could support life
B) a planet or moon that has a strong magnetic field
C) a planet or moon with life
D) a planet or moon on which humans could survive if we happened to go there
9) Which of the following places is not generally considered a potential home for life in our solar
system?
A) Mars
B) Jupiter’s atmosphere
C) Titan
D) Europa
10) The Sun’s habitable zone ________.
A) extends from just beyond the orbit of Mercury to just beyond Earth’s orbit
B) extends from the orbit of Earth to the orbit of Jupiter
C) consists only of Earth, since Earth is the only planet known to be inhabited
D) extends from some place a little beyond the orbit of Venus to some place near the orbit of
Mars
11) Why don’t we expect to find life on planets orbiting high-mass stars?
A) The stars are too hot to allow for life.
B) The lifetime of a high-mass star is too short.
C) Planets cannot have stable orbits around high-mass stars.
D) The habitable zone around a high-mass star would be too far out in space.
12) How might an orphan planet be habitable?
A) if it is captured by another star in that star’s habitable zone
B) if it has enough internal heat to provide an energy source for life
C) if it is made entirely of water
D) if it formed near the center of the galaxy where there are enough nearby stars to provide
sufficient energy for life
13) In 1974, a radio signal containing information about our species was broadcast towards the
globular cluster M13. This target was chosen because of the large number of stars in M13. Why
is it unlikely that an intelligent civilization actually exists in this globular cluster?
A) There are so many stars in globular clusters that collisions between stars are common, which
would destroy any civilization on a planet around those stars.
B) Globular cluster stars are too massive and short-lived to support life.
C) According to the Drake equation, we are the only intelligent civilization in the galaxy.
D) It is unlikely that terrestrial planets exist in globular clusters since these stars formed prior to
significant heavy element production in the galaxy.
14) At present, what is the primary way that the search for extraterrestrial intelligence (SETI) is
carried out?
A) by using radio telescopes to search for signals from extraterrestrial civilizations
B) by searching for planets around distant stars
C) by seeking access to the secret records and alien corpses kept at the military’s Area 51 in
Nevada
D) by using X-ray telescopes to search for exhaust from interstellar spacecraft
E) by analyzing high-resolution images of nearby stars in search of evidence for structures that
could not have developed naturally
15) In the Drake equation (Number of Civilizations = NHP × flife × fciv × fnow), what do we
mean by fnow?
A) the fraction of all species ever to exist that we currently are aware of
B) the fraction of planets in the galaxy on which a civilization could theoretically develop right
now
C) the fraction of civilizations in the universe that currently are sending messages to us
D) the fraction of planets with civilizations at the present time (as opposed to only in the past or
future)
16) We have sent several spacecraft on trajectories that will ultimately take them into interstellar
space (Pioneer 10 and 11, Voyager 1 and 2, New Horizons). How long will it take these
spacecraft to travel as far as the nearest stars?
A) tens of thousands of years
B) a few decades
C) never, because they will rust and fall apart
D) a few hundred years
E) about a thousand years
17) Einstein’s theory of relativity tells us that travelers who make a high-speed trip to a distant
star and back will ________.
A) have more fun than people who stay behind on Earth
B) never be able to make the trip within their lifetimes
C) age less than people who stay behind on Earth
D) age more than people who stay behind on Earth
18) If there are other civilizations at present in the Milky Way Galaxy, which statement is almost
undoubtedly true?
A) They have social structures that are completely different from our own; for example, different
types of “family” units, and so on.
B) They are anatomically much like us, with two arms, two legs, two eyes, and two ears.
C) They are far more technologically advanced than we are.
D) For fun, they enjoy “buzzing” to Earth and temporarily abducting people, showing a clear
preference for people located in less-developed rural areas.
19.6 Mastering Astronomy Concept Quiz
1) Why are fossils of early life on Earth rarer than fossils of plants and animals from the past few
hundred million years?
A) Fossils could not form before there was oxygen in the atmosphere.
B) Early organisms were microscopic and lacked skeletons and other hard structures that are
most likely to be fossilized.
C) Life was far less abundant prior to a few hundred million years ago.
D) We find fossils in sedimentary layers, and no sediments were deposited until just a few
hundred million years ago.
2) Which of the following best describes natural selection?
A) It is the idea that organisms with genetic traits that improve their ability to reproduce are
more likely to pass those traits on to future generations.
B) It is the idea that organisms naturally increase in complexity and intelligence with time.
C) It is a guess made by scientists about how life develops, but it has no hard evidence to support
it.
D) It is the idea that the strong survive and the weak die off.
3) Which of the following is not key evidence in support of the idea that all life today shares a
common ancestor?
A) We have identified fossils of the first life forms that ever existed on Earth.
B) All life uses DNA and the same genetic code.
C) Mapping of gene sequences shows how life is all related.
D) All life builds proteins from the same amino acids and uses ATP to store energy in cells.
4) Which of the following best describes the predominant scientific view of the origin of life on
Earth?
A) We may never know precisely how life arose, but current evidence suggests that life probably
can arise naturally under the conditions that prevailed on the early Earth.
B) We can describe with great certainty the precise steps by which life arose on Earth.
C) Life probably migrated to Earth from some other world.
D) Life arose through a series of extremely unlikely chemical coincidences, making it seem
almost miraculous that life ever came to exist at all.
5) According to current science, why didn’t oxygen begin to accumulate in the atmosphere for
more than a billion years after life appeared on the Earth?
A) Oxygen was removed from the atmosphere by dissolving in the ocean as quickly as it was
released by life.
B) Early life did not release oxygen, and oxygen releasing organisms didn’t evolve for a billion
years after the earliest life.
C) Early forms of animal life consumed the oxygen released by plants during the first billion
years of life on Earth.
D) Oxygen was removed from the atmosphere by chemical reactions with surface rocks as
quickly as it was released by life.
6) When we analyze whether a world is a possible home to life, the key thing we look for is
________.
A) the existence of liquid water
B) the presence of organic molecules such as amino acids
C) surface coloration changes that could indicate vegetative growth
D) evidence of atmospheric oxygen
7) When the Viking landers conducted experiments with samples of Martian soil, they found
what was initially thought to be biological reactions indicative of life. What is the current
thinking regarding these findings?
A) Scientists now think these findings show conclusive evidence that Mars has active
microscopic life in its soil.
B) Scientists now think these findings show conclusive evidence that Mars had life in its soil at
one time, but not currently.
C) Scientists now think these findings are most likely explained by chemical (rather than
biological) reactions.
D) Scientists now think these findings show evidence of silicon-based (rather than carbon-based)
life.
8) Why is Europa considered a good candidate for the possible existence of life?
A) Strong evidence suggests that it has a deep, subsurface ocean of liquid water.
B) It is located within our Sun’s habitable zone.
C) It has a thick atmosphere with a surface pressure greater than that on Earth.
D) The Galileo spacecraft found strange seasonal changes on its surface that look like they could
be due to life.
9) In general, how does the size and location of a star’s habitable zone depend on the star’s mass?
A) The smaller (less massive) the star, the smaller and the closer-in the habitable zone.
B) The habitable zone is always about the same size, but its location moves inward for smaller
stars.
C) The smaller (less massive) the star, the larger and the closer-in the habitable zone.
D) The smaller (less massive) the star, the larger and the farther-out the habitable zone.
10) We are not yet capable of detecting signs of life on terrestrial planets around other stars. But,
as our technology develops, our first real chance of detecting such life will probably come from
________.
A) examining spectral lines from the atmospheres of distant planets
B) sending spacecraft to study the planets up close
C) examining high-resolution images of the planets made by orbiting telescopes
D) determining the orbital properties of the planets
11) Why are plate tectonics thought to be necessary on a planet if it is to support life?
A) Plate tectonics allow water to remain in a liquid state on the surface of a planet.
B) Plate tectonics allow water to remain in a liquid state under the surface of a planet.
C) Plate tectonics allow the water evaporation cycle to operate, which provides long-term
climate stability.
D) Plate tectonics allow the carbon dioxide cycle to operate, which provides long-term climate
stability.
12) Which of the following best describes how the Drake equation is useful?
A) It tells us what wavelengths of light will be most useful to examine in the search for
extraterrestrial intelligence.
B) It helps us understand what we need to know in order to determine the likelihood of finding
other civilizations in our galaxy.
C) It has allowed us to determine the number of civilizations in our galaxy.
D) It allows us to calculate the masses of planets orbiting other stars.
13) In the Drake equation (Number of Civilizations = NHP × flife × fciv × fnow), we expect the
term fciv to be small if ________.
A) most habitable planets never actually develop life on them
B) primitive life is common but intelligent life is rare
C) most of the civilizations that have ever existed are still out and about in the galaxy
D) most civilizations destroy themselves within just a few hundred years of arising
14) Suppose that there are 1000 habitable planets in our galaxy, that 1 in 10 habitable planets has
life, that 1 in 4 planets with life has at some point had an intelligent civilization, and that 1 in 5
civilizations that have ever existed is in existence now. How many civilizations would exist at
present in our galaxy?
A) 1
B) 5
C) 25
D) 100
E) 500
15) If it turns out that many intelligent civilizations have at one time existed in our galaxy, what
is a disturbing conclusion that we could draw from this?
A) It would lend credence to the idea that we are being secretly visited by aliens and that alien
abductions are likely real.
B) It would imply that our technology will never be advanced enough to detect extraterrestrial
intelligence.
C) The fact that we have not been contacted by an intelligent civilization, or seen any evidence
of one, implies that intelligent civilizations are inherently short-lived.
D) It would imply that aliens are plotting to come to Earth and steal our water.
16) Imagine that we make it. We somehow overcome our tendency to start wars, to use our
resources in an unsustainable manner, to destroy our natural habitat. Imagine that we figure out
how to last more than a few more centuries or millennia on this spaceship we call Earth. Imagine
that the drive to explore our universe never leaves us and we develop technology that takes us to
the stars. Imagine that we are the species that develops a galactic civilization. That’s a lot of
imagining…
Assuming a reasonable rate of colonization of star systems, how long would it likely take our
species to spread out through the entire galaxy?
A) billions of years
B) hundreds of millions of years
C) a few million years
D) a few thousand years
17) Which of the following is not considered a potential solution to the question of why we lack
any evidence of a galactic civilization?
A) The galactic civilization probably is undetectable because they operate under different laws of
physics from the ones we know.
B) There is no galactic civilization because we are the first species ever to achieve the ability to
study the universe.
C) There is no galactic civilization because all civilizations destroy themselves before they
achieve the ability to colonize the galaxy.
D) The galactic civilization is deliberately avoiding contact with us.