Download Conditions for Life

Grade 7
Science
Unit: 05 Lesson: 01
Conditions for Life
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.
Earth’s Atmosphere from Space Source: NASA, http://www.nasa.gov/images/content/285744main_PIA11066_full.jpg
License: Public Domain
©2013, TESCCC
05/06/13
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Grade 7
Science
Unit: 05 Lesson: 01
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.
©2013, TESCCC
05/06/13
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