1.
Is There Life on Other Planets?
A Teachers’ Choice Library Unit
By
Dean Berry, Ed. D.

2.
Does life exist beyond earth?
Read, Discuss, Research, and Write
As we progress through this unit for the next few days, you
will read and discuss information about the possibility of
life beyond earth. Listening and speaking skills will be
practiced. Evaluating claims and supporting evidence will
be a primary focus along with research and writing skills.

3.
Before we can answer the question
about life on other planets, we need
to explore the origin of the universe.

4.
Scientists generally agree that the universe
began about 12.4 billion years ago with an
explosive event called the big bang theory.

5.
The Big Bang Theory asserts that before the
universe existed, a tiny particle exploded and
inflated at tremendous speed into matter that
included protons and neutrons.

6.
This exploding matter eventually created the galaxies
containing stars and planets. As a result, stars and
planets are composed of similar elements but in
different quantities. What is our sun? How was it
created? Read more to find out.

7.
Our sun was created from star dust and gases in
the universe about 5 billion years ago. The left
over dust and gas revolved around the sun until
gravity helped create the planets and their orbits.

8.
The solar system is made up of eight planets-four with
rocky, hard surfaces and four that are gas giants. Which
two planets are closest to earth? Why do you think that
one of these planets might have the best chance of all of
the solar system planets to support life?

9.
Planets are gas or terrestrial(rocky land) space objects that
are larger than asteroids and orbit stars. They were created
from left over star gas and dust that became round in shape
as gravity acted on them during the orbiting process.

10.
Understanding gravity is important in helping us
understand the universe. Gravity moves objects with mass
closer together. Larger objects with more mass have a
stronger gravitational pull. The sun’s gravity pulls the
planets into orbit. What would happen to us if the earth
didn’t have any gravity?

11.
The gravitational pull of our moon is what causes
our ocean tides. If you were standing on the moon,
would you be able to spin five times in the air and
dunk a basketball even if you were a short person
with limited athletic skill?

12.
Examine the information below. What conclusion
can you draw about the size of mars in relation to
the size of Earth? What would you expect the
gravity of the moon to be like?

13.
Think about the impact gravity has on objects. Analyze
these rocket speeds as each rocket leaves it’s planet.
Consider the size of each planet in our solar system.
Knowing that each rocket has the same power lift, what
conclusion can you draw about the impact of gravity as it
relates to objects?

14.
As objects that contain metallic substances spin around,
they create electrical charges that cause a magnetic field
to form around the object. In space, these objects can be
asteroids, planets, and stars. The Earth is like a giant
magnet with north and south magnetic poles. As far as we
know, most planets and stars have magnetic fields if they
spin at a fast rate of speed. For example, Venus does not
have a detectable magnetic field because it spins slowly.

15.
Magnetic fields are possible when Electrons
orbiting within an atom are unpaired and capable
of aligning in an electric formation.

16.
Over 100 years ago a brilliant scientist developed a
revolutionary theory that helped the world understand
how the universe works. Einstein’s theory of relativity
went beyond the three dimensional realty that we see
every day to a 4th dimension of time that is referred to
as the time/space continuum.

17.
Theoretically, one could one could go
back in time or into the future since
gravity is the consequence of the
curvature of space/time caused by the
uneven distribution of mass/energy.

18.
With the 4th dimension in outer space, time warps
and worm holes become interesting possibilities for
forms of advanced life to travel throughout the
universe to distant locations like earth. What are
worm holes?

19.
The theory of relativity demonstrates that all lines are curved in
space. For example, the latitude and longitude lines actually curve
as they cover the earth. Going faster than the speed of light could
enable one to cross over into the future. Unfortunately, it is not
possible for any object to exceed the speed of light.

20.
Since the theory of relativity supports the possibilities of worm
holes in time, we have to consider the chances that aliens could
figure out ways to engage in time travel. Of course, any space
traveler would have to beware of black holes capable of
swallowing anything within their gravitational pull. Black holes
remain invisible because they swallow all light and matter while
performing like a magician who makes everything disappear.

21.
Most of our planets have atmospheres with
different kinds of gases. In total, our planets
combine for 140 moons. Do you think life exists on
any of these planets and moons? Why?

22.
Four and a half billion years ago the earth
and other planets in our solar system were
formed from the left over dust and gasses
after the sun was created.

23.
Less than a 100 million years after the earth
was formed, a giant meteor about the size of
mars crashed into the earth and the material
and dust that resulted formed the moon.

24.
The newly created earth was extremely hot and
inhospitable to life. However, after a billion years, the earth
cooled and the gases in the atmosphere changed.

25.
With a much cooler earth and all of the necessary
elements, microscopic life was created about 3.5 billion
yeas ago. Exactly what processes came together over
millions of years to create the first cell is still a mystery
to scientists. We do know that compounds rather than
pure elements were needed in the process.

26.
Which compound makes up over 65% of the human
body? Which two elements are combined to create
this compound?

27.
Other compounds necessary in creating
life include organic compounds such as
carbohydrates, proteins, vitamins, and
enzymes.

28.
Although life as we know it requires approximately
25 different elements, the six elements that
compose 95% of living organisms include carbon,
hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

29.
In order for life to develop, it was necessary
that the elements required for life be
converted into cells with DNA capable of
replicating.

30.
The only way for the original cell to pass on the
requirements for life to another cell was to have a structure
with chromosomes and genes that could be inherited by the
process of cell division. How long do you think it took for
single cells to become human beings? What do scientists
call this transition from lower forms of life to more
advanced forms of life?

31.
The evolution of life on earth flowed from
elements to compounds to cells with DNA
to humans. What does the word evolution
mean?

32.
It took approximately three and a
half billion years for single cells to
evolve into the early Homo sapien
ancestors of modern man.

33.
The first life on earth began in the ocean
with the creation of microorganisms. Does
this suggest that all living creatures are
genetically related to fish? So, maybe
mermaids really do exist(not).

34.
It took several billion years for microscopic
cells to evolve into giant reptiles. The first
dinosaurs roamed the earth approximately
230 million years ago.

35.
If the earliest giants of the earth were reptiles,
where did mammals come from? Scientists believe
that flying dinosaurs evolved into birds.

36.
Over 100 million years ago a branch of reptiles begin to
acquire characteristics that eventually evolved into our
current idea of mammals. Fortunately for us, one type of
mammal became similar to chimpanzees, our kissing
cousins. Are humans really related to apes? Explain

37.
Around 8 million years ago the ancestors of chimps
evolved slowly into creatures that could walk
upright until they began to resemble early man.
What kind of evidence do you think supports the
idea that humans evolved from chimpanzees?

38.
The human genome contains 96% of the same
genes found in chimpanzees. This means that we
have nearly all of the genetic blueprints and DNA
sequences found in chimps and their close relatives.

39.
Watch this one minute animated illustration of the
evolution from microscopic organism to human
being. This process took millions of years. Where
does this video suggest that life began? Can you
retell the story of evolution after watching this
video clip?

40.
If life could evolve on earth, is it reasonable to
assume that life could evolve somewhere else
in the universe? Why? Or Why not?

41.
Is it likely that advanced forms of life know
about us but are not interested in visiting us
at this point? Why might that be the
case?

42.
Do you believe people who say they have
been kidnapped and taken for rides in
alien spaceships? Why? Why not?

43.
Our modern civilization has undergone tremendous
advancements in technology that have enabled our
world to explore other worlds. What were some of
these important technological advancements?

44.
Three and a half billion years after the
beginning of life on earth, the United States
used rocket technology to reach the moon.

45.
By 1968, the United States used the Apollo 8
mission to achieve the first manned space
flight to orbit the moon. Did we find any
evidence that life existed on the moon?

46.
In 1969, American astronauts walked on the
moon for the first time in history. During the
next three years, the United States had five
more manned landings on the moon.

47.
Scientists have determined that the mineral composition of
the moon closely matches that of earth. This fact alone, is
more evidence that the moon is composed of material
derived from earth. Unfortunately, we have not found
evidence of life on the moon.

48.
After putting a man on the moon in 1969, the
United States turned its space exploration toward
mars. Why do you think we chose to investigate
mars rather than other planets?

49.
Mars is a planet that holds promise for the
existence of life. It has a very cold surface with
polar ice caps, seasons, volcanoes, and canyons.
It is also a very close neighbor to earth.

50.
The United States has been exploring the surface
of mars for over forty years with robots called
rovers. As a result, it has been determined that
mars has clear evidence of water. There are
definite signs of ancient floods. The existence of
water is crucial since scientists believe it is
necessary to sustain life.

51.
In 1971, the United States sent Mariner 9 to
be the first space craft to orbit mars. By
1976, Viking 1 landed on mars with a rover
capable of taking photographs.

52.
During the last couple of years, our space program
has been collecting important samples of materials
below the surface of the red planet. Scientists are
hoping to find evidence that mars either has some
form of life or has supported life in the past.

53.
We have explored parts of our solar system in search of
alien life forms. What are the chances that we will find
evidence of life on planets or moons in our solar system?
What kind of evidence would persuade you that life has
existed elsewhere in our solar system?

54.
Will we find life anywhere in the
universe other than Earth?
Life as we know
it requires water,
carbon,
hydrogen,
nitrogen, oxygen,
phosphorus and
sulfur.

55.
Scientists have concluded that all life on earth evolved
from the same original cell that ignited the creation of
life over 3.5 billions years ago. Significantly, there has
not been any creation of life on our planet except life
that has evolved from the original first cell. So for the
last 3.5 billion years life was created just one time. What
does this suggest about the likelihood of life being
created on other planets?

56.
Another factor that scientists use to evaluate the
probability of life beyond earth is the number of
planets that exist in the habitable zone around
stars. Only a small fraction of planets are located in
these desirable zones around stars. Why do you
think that scientists created a prediction model that
uses habitable zones for their estimates of life?

57.
Astronomers like to use the Drake Equation as a tool to
predict the odds of finding intelligent life beyond our earth.
This equation uses multiple factors to estimate the
chances of extraterrestrial life. There appears to be at
least 100 to 200 billion planets in our milky way galaxy and
scientists estimate that billions of these planets have what
will be necessary for life as we know it. Therefore, it is
probable that billions of planets in our galaxy have the
prerequisites for life. Consider this large number and factor
in the latest estimate of how many galaxies may be in the
universe and the number becomes immense. Most
scientists believe the universe may have as many as two
trillion galaxies. What can you conclude from reading this
paragraph?

58.
Can we be sure that life was spawned on earth rather
than transported here by an advanced alien civilization?
Some scientists support the directed panspermia theory
which proposes that advanced civilizations brought life to
earth as an experiment. Others suggest that life could
have been brought from outer space accidentally on a
meteorite. What do you think about these theories?

59.
If life exists beyond earth, what might it
look like?
What forms of life might we discover on
other planets or solar systems?

60.
Draw a sketch of a possible example
of an alien from outer space. Share
your drawing with the class.

61.
Do you really believe that aliens will look like us?
If these are real forms of life on earth today, what
can we expect life to look like on other planets?

62.
Is it likely that aliens from outer space
have visited earth? What kind of
evidence would prove the existence of
aliens?

63.
Do you think that aliens are probably far more
advanced than we are? Or, do you expect life
on other planets to be more primitive than life
on Earth? Why?

64.
Some people believe that unusual phenomena from
our distant past is evidence that we have been
visited by aliens from outer space. Ancient drawings
that show space craft may suggest that aliens have
been to earth.

65.
Etched into a high plateau in Peru’s Nazca Desert, a
series of ancient designs raise serious questions about
who created them. Some ancient alien theorists claim
that since the Nazca drawings are so huge and can only
be viewed clearly from the sky, they must have been
drawn by aliens from outer space who visited two
thousand years ago.

66.
The Nazca designs in Peru extend for over 50 miles
and include simple , geometric lines depicting
animals, birds, and humans. Some of the creations
measure more than 600 feet across.

67.
About two thousand years ago in India, ancient drawings
were made on large stones. These drawings included a
variety of flying machines called vimanas. Some alien
theorists suggest that these drawings are of alien space
craft that visited our world in the past.

68.
On a small island off of the west coast of South America
there is another unexplainable phenomena. Easter
Island is the home to over 880 enormous stone statues
carved with human features. The largest stones are up
to 33 feet tall and weigh up to 75 tons.

69.
Some people have suggested that these incredibly huge
statues are too big to have been carved and moved by
humans. They suggest that ancient alien visitors must
have created them. Other experts say that the ancient
Polynesians figured out a special way to move the stones.

70.
So the question remains the same. Do
we have enough supportable evidence
that life exists beyond our earth?

71.
It is important to know that life on this planet is a form
of carbon chemistry. It starts with photosynthesis which
takes carbon dioxide and water and makes it into
complicated compounds which get incorporated into
living things. It continues with DNA which enables cells
to replicate themselves.

72.
Carbon is abundant throughout the universe. It is one of
the most common elements produced in stars. All forms
of life ever encountered on earth require carbon. Thus,
carbon chemistry is most likely the basis for any life
forms elsewhere. What happens when you burn anything
that was originally alive? Will you get the same result by
burning newspapers and dead animals? Explain

73.
In 1994, while digging through the Antarctic ice, scientists
discovered a meteorite that was determined to be from
mars. After several years of scientific analysis and debate,
scientists agreed that the meteorite did not contain any
materials that suggested the possibility of life. However, we
continue to explore more areas of mars for any signs of life.

74.
In addition to mars, Jupiter’s moons have provided
new places to search for life. Several of the moons
that orbit Jupiter appear to have suitable
environments for living organisms.

75.
Europa is the best candidate of the moons around
Jupiter to provide clues as to the existence of life
beyond earth in our solar system.

76.
We know that the vast majority of planets in
the universe have extreme climatic
conditions that preclude life as we know it.

77.
But there are many planets in the
universe that could support life as
we know it.

78.
This sulfuric lake contains
microscopic life. If life on Earth can
thrive in chemical lakes like these, it
may exist on distant planets.

79.
What might alien life look like? Can you
describe some possibilities?

80.
Have You Ever Seen One of These? Well, they live
right here on Earth.

81.
Could these newly discovered creatures
on Earth be like life on other planets?

82.
Maybe these fellows aren’t so weird!

83.
Read the following two articles about the
possibility of finding life beyond our own earth.
As you read these articles, identify and
record any claims or logical arguments
that support the pro and con position
about the likelihood of finding life on
another planet. You will use your notes
to write an argumentative essay about
finding alien life forms in the universe.

84.
An Argument for Life on Other Planets
The number of stars in our galaxy are around 200
billion.
Also used in the equation is the number of stars
that would have planetary systems, how many of
those planets could support life, and on how many
of those planets would life evolve, with an
intelligent life.

85.
Our space program and those of other nations have
been for several years, sending probes out into our
solar system, and among other things being
accomplished, they are looking for other life on
those adjacent planets to ours. The Hubble
telescope has given us glimpses at objects that a
few years ago no one dreamed we'd ever be able to
see. I think many of us would like to know (and
probably even hope), that we are not the only living
thing in the universe.
What is the author hoping for?

86.
Our knowledge is so limited however, that we are still
searching our closest neighbor for that information. I'm
not implying that we haven't had success in some of our
ventures, but when you think of the possibility that there
may be 200 Billion stars just in our galaxy, according to
Drake's equation, surely some of which can have planets
similar (or not similar) to ours, the odds are pretty high for
finding other life forms.
The author claims that the odds for finding planets
with life are pretty high. What evidence does the
author provide to support this claim?

87.
I envy those being born today for what
they may learn in their lifetime, while on
the other hand, I hope that we leave that
opportunity for them to learn.
Technology is proceeding forward at a
faster rate than it ever has in our
existence on this planet.
Why does the author envy younger
people?

88.
• Some researchers indicate that our planet earth is about
4.6 billion years old. The oldest known direct evidence of
life on earth is a fossilized bacteria found in 3.5 billion-
year-old rocks from Western Australia, as announced by J.
William Schopf of the University of California at Los
Angeles in 1993. The technology we enjoy today has only
been developed in the past 100 years, so can we imagine
what will be forthcoming in the next 100 years?
• What is the author suggesting about the rate of future
discoveries?

89.
We are unique in the location of our planet within
our solar system and galaxy, which surely had a
vital affect on it being habitable. What we have
developed into has been our choice. What we
leave for our children and grandchildren is also
our choice. I hope we make the right decisions.
What is the author implying about humans and
their use of the planet?

90.
Life on Saturn’s Moons: Enceladus,
Titan, and Jupiter’s Europa?
Understanding the oddities of life in our most
extreme regions leads us to wonder: Is life on
Enceladus, Titan, or Europa possible?

91.
Enceladus is the brightest moon in our solar system.
It is composed entirely of ice, fully reflecting light.
In 2005, the Cassini spacecraft photographed
geysers of ice and water vapor being expelled at
least 300km into space, so there must be liquid
water under the moon’s icy surface, and sufficient
heat internally to propel ice into water vapor.
Why is the author optimistic about the
possibility of the moon, Enceladus, high a
chance for life?

92.
Titan is the only moon in our Solar System that has a
substantial atmosphere (it is mostly nitrogen). When the
Cassini spacecraft dropped the Huygens probe into Titan’s
atmosphere, the probe found ammonia and methane. Lakes
of methane are clearly visible, as you can see from the
image above. Ammonia and methane could theoretically
combine, in an electrically charged environment, to make
organic compounds, and extremophile bacteria similar to
those found in deep ocean hot springs on Earth. It would
seem that extremophile bacteria could survive in this
methanological system.
Why does the author think that the discovery of
ammonia and methane are positive indications for
finding life?

93.
Europa, the second moon of Jupiter, has
an icy surface with a suspected liquid
ocean below the surface. Life similar to
that of subglacial regions is possible on
Europa as well.

94.
Stephen Hawking, Renowned Scientist
Life in the Universe
• What are the chances that we will encounter some alien
form of life as we explore the galaxy? If the argument
about the time scale for the appearance of life on Earth is
correct, there ought to be many other stars whose
planets have life on them. Some of these stellar systems
could have formed 5 billion years before the Earth. So
why is the galaxy not crawling with self designing
mechanical or biological life forms?
• What does the author mean by self designing mechanical
life forms?

95.
• Why hasn't the Earth been visited, and
even colonized. I discount suggestions
that UFO's contain beings from outer
space. I think any visits by aliens would
be much more obvious, and probably
also, much more unpleasant.
• Does the author believe that earth has
been visited by aliens? Why or why not?

96.
• What is the explanation of why we have not been visited?
One possibility is that the argument about the appearance
of life on Earth is wrong. Maybe the probability of life
spontaneously appearing is so low that Earth is the only
planet in the galaxy, or in the observable universe, in
which it happened.

97.
• Another possibility is that there was a reasonable
probability of forming self reproducing systems, like
cells, but that most of these forms of life did not evolve
intelligence. We are used to thinking of intelligent life, as
an inevitable consequence of evolution. But the
Anthropic Principle should warn us to be wary of such
arguments. It is more likely that evolution is a random
process, with intelligence as only one of a large number
of possible outcomes.
•Why does the author think that finding
intelligent life may be a remote possibility?

98.
• It is not clear that intelligence has any long-term survival
value. Bacteria, and other single cell organisms, will live
on, if all other life on Earth is wiped out by our actions.
There is support for the view that intelligence, was an
unlikely development for life on Earth, from the
chronology of evolution.
• What does the author believe about finding intelligent life
beyond Earth?

99.
• It took a very long time, two and a half billion
years, to go from single cells to multi-cell beings,
which are a necessary precursor to intelligence.
This is a good fraction of the total time available,
before the Sun blows up. So it would be
consistent with the hypothesis that the
probability for life to develop intelligence is low.
In this case, we might expect to find many other
life forms in the galaxy, but we are unlikely to
find intelligent life.
•What is the conclusion reached by this
author? What argument does the author use
to support this conclusion?

100.
• Another way, in which life could fail to develop to an
intelligent stage, would be if an asteroid or comet were
to collide with the planet. We have just observed the
collision of a comet, Schumacher-Levi, with Jupiter. It
produced a series of enormous fireballs. It is thought the
collision of a rather smaller body with the Earth, about
70 million years ago, was responsible for the extinction
of the dinosaurs. A few small early mammals survived,
but anything as large as a human, would have almost
certainly been wiped out. It is difficult to say how often
such collisions occur, but a reasonable guess might be
every twenty million years, on average.
What does the author suggest as to why
some planets may have had intelligent life in
the past, but no longer have it?

101.
• If this figure is correct, it would mean that intelligent life
on Earth has developed only because of the lucky
chance that there have been no major collisions in the
last 70 million years. Other planets in the galaxy, on
which life has developed, may not have had a long
enough collision free period to evolve intelligent beings.
•What does the author suggest as a possible
block to finding intelligent life?

102.
• A third possibility is that there is a reasonable
probability for life to form, and to evolve to intelligent
beings, in the external transmission phase. But at that
point, the system becomes unstable, and the intelligent
life destroys itself. This would be a very pessimistic
conclusion. I very much hope it isn't true. I prefer a
fourth possibility: there are other forms of intelligent life
out there, but that we have been overlooked. There used
to be a project called SETI, the search for extra-
terrestrial intelligence.
•Why does the author think that there may be
intelligent life in the universe but we have
never been contacted by them?

103.
• It involved scanning the radio frequencies, to see if we
could pick up signals from alien civilizations. I thought
this project was worth supporting, though it was
cancelled due to a lack of funds. But we should have been
wary of answering back, until we have developed a bit
further. Meeting a more advanced civilization, at our
present stage, might be a bit like the original inhabitants
of America meeting Columbus. I don't think they were
better off for it.
• What does the author suggest as a reason
why we should be careful about responding
to possible alien communication?

104.
What are the chances of
life on another planet?
May 9, 2016
•In an infinite universe, most scientists
agree, the odds of life existing on a
planet besides Earth are pretty high. It is
unlikely, however, that familiar life forms
will be found on any planet within our
solar system.

105.
• Life as we know it—everything from single-celled
organisms to human beings—consists largely of liquid
water. So a planet that harbors life can't be too cold or
water will freeze, nor can it be too hot or all the water
will evaporate. Planets closer to the sun than Earth are
too hot, and those farther away are too cold. The surface
of Venus, for example, is hot enough to melt lead, and
would vaporize any living thing, while the surface of
Mars is frozen solid.
•What reasons does the author offer as to
why he believes that finding life beyond
Earth in our solar system is unlikely?

106.
• Life as we know it here on Earth also requires a
magnetic field and an atmosphere, both of which protect
it from the lethal radiation our parent star, the sun,
emits. Earth's magnetic field—generated by its rotating
iron core—deflects the solar wind, a continuous stream
of high-speed, high-energy particles coming out of the
sun. (As those particles careen by the edges of Earth's
atmosphere, they sometime create the phenomenon we
call the Northern Lights.) Without the magnetic field
there, the solar wind might destroy all life on Earth.
•Why does the author indicate that a
magnetic field would be necessary if a
planet were to sustain life?

107.
• As for Earth's atmosphere, it protects life because the
water, carbon dioxide and other gases in it absorb solar
radiation in its harmful ultraviolet-light form. The parent
stars of other solar systems would emit radiation as
well, and the planets orbiting them would need the same
kind of protection.
• Why would an atmosphere be important for
a planet with life?

108.
• Of course, life on Earth also alters the chemical
composition of the atmosphere—Earth's atmosphere
lacked gaseous oxygen until plants started growing
here some million years ago. So molecules like oxygen
in the atmosphere of another planet would be one
indication—not proof—that there are living things there.
•What does the author suggest might
increase the odds of finding life on a
planet?

109.
• Scientists have been studying the planets of our own
solar system for more than 50 years, looking for evidence
of past or present life, among other things. Launched in
1967, the Soviet Union's Venera 4 was the first probe
known to land on and send back data from another planet.
The mission revealed that Venus' famously soupy
atmosphere is made up almost entirely of carbon dioxide
with a surface temperature hot enough to melt lead,
making it a very unlikely place to harbor life.
•Why has Venus been ruled out as a planet
that might have life?

110.
• Today, NASA's Mars rover, Opportunity, has been
sending back reams of data about the red planet since
it landed there 12 years ago. Living well past all
expectations, Opportunity not only transmits landscape
photos and the occasional tweet, but also collects and
analyzes soil and atmosphere samples. It's been an
invaluable research tool, but has found no direct
evidence that life ever existed on Mars, and has
revealed that the planet's atmosphere is too thin to
protect it from the sun's radiation.
•According to the author, should we be
optimistic or pessimistic about life on
Mars?

111.
• The discovery of thousands of planets orbiting nearby
stars has nevertheless greatly increased speculation that
there may be some kind of life on a planet outside our
solar system. In the past 20 years, we have confirmed
the discovery of almost 2,000 planets, called exoplanets,
beyond our solar system. Four thousand other exoplanet
candidates await confirmation.
•What are exoplanets?

112.
• The ones most likely to harbor life would be smallish,
rocky planets like Earth. Larger planets tend to be
composed of hydrogen gas, the most abundant element
in the universe, and to not have a solid surface. Good
candidates for life would also occupy what scientists
call the habitable zone—the zone in which a planet's
distance from the parent star makes liquid water
possible.
•According to the author, what is the
habitable zone?

113.
• The Kepler mission—a space observatory launched by
NASA in 1997 to search our galaxy for just these kinds
of Earth-like planets—has found one candidate that
meets both requirements, Kepler-452b. So the chances
of life on another planet are high. However, we have no
direct evidence yet of life anywhere other than Earth.
•What was the Kepler mission and why was
it important?

114.
• The real question is, will we ever find the planet we're
looking for, given that we'll have to survey the planetary
systems of the universe's estimated 1 billion trillion
stars? And if we do find that planet, will we even
recognize the life it harbors? There's no real reason why
we should expect to discover life as we know it orbiting a
star many light years away from our home solar system.
There's so much we don't know that we are severely
limited in our ability to even think about the question.
• According to the paragraph, why does the
author have doubts about finding life
elsewhere in the universe?
• Read more at: http://phys.org/news/2016-05-chances-life-planet.html#jCp

115.
Group Discussion
Meet in groups and discuss the following.
• 1. What are some of the reasons that support the idea that life as we
know it exists somewhere in the universe other than the planet Earth.
• 2. What are some of the reasons that suggest that life on other
planets will not be discovered any time soon and maybe not at all.
• 3. What kind of materials or conditions are probably necessary for life
to develop on other planets?

116.
Prepare to Write
Write a pro and con essay discussing the probability of life on other
planets. Include a description of the materials and conditions
necessary for life as we know it. Review the development of life on
earth and how it might support the idea that life can or cannot exist
else where in the universe.

117.
Research Websites
• 1. Space.com
• 2. Universetoday.com/33150/life-0n-other-planets/
• 3. science.howstuffworks.com/space/aliens
• 4. wonderopolis.org
• 5. mysteriousuniverse.org
• 6. earthguide.ucsd.edu/virtualmuseum