
Part I
 The Sun is a star located in the center of our Solar System. The Sun is a huge
sphere composed of super-heated gases (plasma). The Sun’s gravitational pull
holds the Earth and the other planets in orbit. Without the Sun, the Earth and
other planets in our solar system would float off into space as a result of the
absence of the Sun’s gravity. The Sun’s energy influences all of the objects in
our solar system differently depending on the distance. The Earth’s distance of
149.60 million km allows the perfect temperature for life to exist on Earth.
 The Sun is categorized as a yellow dwarf. When being compared to other stars
the Sun is average in its size, age, and temperature. It’s predicted by
astronomers that the Sun is approximately 4.6 billion years old and will keep
shining and growing for about another 7 billion years.
 The Sun’s energy is the first source of energy in the food chain. Without the
Sun’s energy, life could not exist on Earth. The Sun drives the Earth’s seasons,
climate, and ocean currents. The oceans also store the Sun’s energy, thereby
creating wind in the Earth’s atmosphere. The wind from the atmosphere
regulates the temperature of the Earth, allowing life of various organisms to
exist
 Part II
 The Earth is surrounded by a thin buffer of air called the atmosphere
which is held around the Earth by the force of gravity. Not only is it the air
we breathe, but it also acts as a protective shield from harmful radiation
and meteorites. The atmosphere allows life to exist on the Earth. Without
the atmosphere, we would experience extreme heat during the day and
extreme cold at night. Look at a photo of the Earth from space. The
atmosphere can be compared to a single layer of skin on an onion. As you
look at the photo of Earth from space, notice how thin the atmosphere is.
The blue glow surrounding the Earth is its atmosphere. The Earth’s
atmosphere is made up of three-fourths nitrogen, and most of the rest is
oxygen. The atmosphere allows evaporating water to form clouds and
produce rain. The atmosphere is a contributor to photosynthesis where
plants continually replace oxygen by using carbon dioxide during the
process.
 Part III
 The temperature on Earth does not go from one extreme to the other. There are
areas of extreme cold and heat, but overall, the Earth’s climate is stable. This is
due to Earth’s distance from the Sun as it orbits around it and its axial tilt
during rotation. Look at a globe of Earth. Notice the 23½° tilt of the Earth on
its axis. If the Earth did not keep this angle during rotation, the seasons would
be very different as the Earth revolved around the Sun. Locate the area in which
you live in on the globe. What is the climate and season like in your area?
 Water may be the most important component necessary for life to exist on
Earth. Water doesn’t burn the skin like some acidic liquids. It is drinkable and
allows life sustaining molecules to be carried through the body. Some moons in
the solar system may contain frozen water. Europa, one of Jupiter’s moons, is
thought to have oceans of water under its frozen surface. What makes water on
the Earth unique is that it can exist on the planet in all three states: liquid in
oceans, lakes, rain, etc.; solid in glaciers and frozen bodies of water; and
gaseous in invisible water vapor.
 Water vapor is vital to weather and climate, and it helps regulate Earth’s
temperature. Clouds, rain, and snow require water vapor in order to form.
Evaporating water prevents the Earth’s surface from getting too hot, just as
sweat evaporates from the body to keep it from getting too warm. Water vapor
is one of the most important natural greenhouse gases which help to keep the
surface warm enough to support life.
 Part IV
 All planets receive light from the Sun. Among other factors, the amount and length of
time each planet is exposed to periods of light and darkness can have an effect on the
possibility of plant life surviving on it. The length of time it takes Earth to spin (rotate)
on its axis is just under 24 hours. Each side of the planet receives sunlight regularly, 12
hours of darkness and 12 hours of light (may be less or more depending upon proximity
to poles). Compare the period of rotation of Earth to that of Venus. It takes 243 days for
Venus to complete one spin on its axis. Even if Venus could support plant life, it would be
difficult for plants to undergo photosynthesis with half of the 243 days being spent in the
dark! Remember that plants convert energy from the Sun, remove carbon dioxide from
the atmosphere, and replace it with oxygen.
 The following summarizes what is necessary for life to exist on Earth:
 The proximity of the Sun to Earth determines the amount of heat and light the Earth will
receive.
 The availability of liquid water for use by living organisms and the presence of water
vapor necessary to the formation of weather and climate
 A non-poisonous atmosphere composed of gases that enable organisms to survive
 Other forms of life, different from those we see on Earth, may exist in our solar system.
These possible life forms may require different conditions to exist.