changing all the time.
Ozone in the Upper Atmosphere Makes Life on Earth Possible
Ozone is a molecule composed of three oxygen atoms, (O 3 ). Ozone in the upper atmosphere
absorbs high energyultraviolet radiation(UV) coming from the Sun. This protects living
things on Earth’s surface from the Sun’s most harmful rays. Without ozone for protection,
only the simplest life forms would be able to live on Earth.
The Atmosphere Keeps Earth’s Temperature Moderate
Our atmosphere keeps Earth’s temperatures within an acceptable range; the difference be-
tween the very coldest places on Earth and the very hottest is about 150oC (270oF). Without
our atmosphere, Earth’s temperatures would be frigid at night and scorching during the day.
Our daily temperatures would resemble those seen on the Moon, where the temperature
range is 310oC (560oF) because there is no atmosphere. Greenhouse gasestrap heat in
the atmosphere. Important greenhouse gases include carbon dioxide, methane, water vapor
and ozone.
Atmospheric Gases Provide the Substance for Waves to Travel
Through
The atmosphere is made of gases, mostly nitrogen and oxygen. Even though you can’t see
them, gases take up space and can transmit energy. Sound waves are among the types of
energy that can travel though the atmosphere. Without an atmosphere, we could not hear a
single sound. Earth would be as silent as outer space. Of course, no insect, bird or airplane
would be able to fly since there would be no atmosphere to hold it up!
Composition of Air
Air is made almost entirely of two gases. The most common gas is nitrogen, and the second
most common gas is oxygen (O 2 ). Nitrogen and oxygen together make up 99% of the planet’s
atmosphere. All other gases together make up the remaining 1%. Although each of these
trace gases are only found in tiny quantities, many such as ozone, serve important roles
for the planet and its life. One very important minor gas is carbon dioxide, CO 2 , which is
essential for photosynthesis and is also a very important greenhouse gas (Table(15.1).