Atmosphere: Composition and Structure
What is the Atmosphere?
The atmosphere is the blanket of gases which surrounds
Earth. It is held near the surface of the planet by Earth's
gravitational attraction.
Without the atmosphere there could be no life on Earth. The
atmosphere:



contains the air we breathe;
protects life from harmful radiation from the Sun;
helps keep the planet's heat from the Sun from escaping
back into space;
 is a major element of the water cycle;
 keeps the climate on Earth moderate compared to that of
other planets.
Composition of Earth’s Atmosphere
The atmosphere is made up of a mixture of gases, mostly
nitrogen, oxygen, argon and carbon dioxide. It reaches over
500km above the surface of the planet. There is no exact
boundary between the atmosphere and outer space.
Atmospheric gases become thinner the higher up you go. The
atmosphere just keeps getting less and less dense, until it
"blends" into outer space.
Name
Percentage (%)
Nitrogen
78%
Oxygen
21%
Argon
0.93%
Trace gases
0.1%
Layers of the Atmosphere
The atmosphere has 4 layers: the
troposphere that we live in near the
surface of the earth; the stratosphere
that houses the ozone layer; the
mesosphere, a colder and lower density
layer with about 0.1% of the
atmosphere; and the thermosphere, the
top layer, where the air is hot but very
thin.
Definitions:
Layers of the
Atmosphere
Troposphere
Altitude
Temperature
20km
Decreases
Stratosphere
50km
Increases
Mesosphere
85km
Decreases
Thermosphere
690km
Increases

The Troposphere
- This is the lowest layer of the
atmosphere, closest to the surface of the
earth. The troposphere varies in height in
different parts of the world, from about
8km above sea level at the poles, to
16km at the equator. Within the
troposphere, the temperature drops
rapidly the higher you go.
-This is the layer where we see clouds
and most of the "weather" occurs.

The stratosphere
- For a distance of about 18km above
the tropopause, there is a layer called
the stratosphere. In this layer, the
pressure continues to decrease, but the
temperature increases gradually to 0ºC.
- The stratosphere contains a layer of
ozone which absorbs the Sun's
ultraviolet rays, protecting life on the
earth's surface.
- The top layer of the stratosphere is
called the stratopause. In this layer the
temperature, once again, begins to fall.

The Mesosphere
- the layer above the stratosphere. The
temperature decreases with height here
just like it does in the troposphere. This
layer also contains ratios of nitrogen and
oxygen similar to the troposphere,
except the concentrations are 1000
less and there is little water vapor there,
so the air is too thin.


Altitude – the height of an object or
point in relation to sea level or ground
level.
Temperature - a measure of the
warmth or coldness of an object or
substance with reference to some
standard value.

The Thermosphere
- It is the uppermost layer of the
atmosphere. In this layer the
temperature increases with height
because it is being directly heated by
the sun. The thermosphere extends
upwards from a point 80-100 kilometers
above the earth's surface. There is very
little air in this layer.

The Exosphere
- The exosphere is the very outer limit
of the atmosphere. The bottom of this
layer is found at 500 kilometers above
the Earth's surface. The pressure drops
to little more than a vacuum. Auroras
form in the exosphere.
Bibliography
Structure of the atmosphere. Retrieve from https://climate.ncsu.edu/edu/Structure
Cloud1.arc.Retrieve fromhttps://cloud1.arc.nasa.gov/solveII/outreach/middleschool-atmos.htm
Hobbs, P. V. Introduction to Atmospheric Chemistry. New York: Cambridge University Press,
2006.Retrieve from https://www.encyclopedia.com/science/encyclopedias-almanacstranscripts-and-maps/atmosphere-composition-and-structure