The atmosphere is divided into four main layers - the troposphere, stratosphere, mesosphere, and thermosphere. Each layer is defined by changes in temperature. The troposphere extends from Earth's surface to around 12 km and contains around 90% of the atmosphere. The stratosphere extends from 12-50 km and contains the ozone layer which absorbs harmful UV radiation. Air is composed primarily of nitrogen (78%) and oxygen (21%).

1. The Atmosphere
• The sun’s energy interacts with
Earth’s atmosphere and the oceans,
providing Earth’s climate and
weather and produce the clouds,
winds, storms, rains, etc.

2. The Structure of the
• Troposphere Atmosphere
–Temperatures
decrease with
altitude 16oC 
-60oC

3. The Structure of the
• Troposphere Atmosphere
–The air is warmed by heat
radiating from Earth’s surface, the
evaporation of water vapor, and
water vapor condensing back to
Earth.
–Extends from Earth’s surface
upward 12 km (7 miles) and
contains 90% of the atmospheric
gases.

4. The Structure of the
Atmosphere (cont’d)
• Stratosphere
– The tropopause (the
dividing line
between the
troposphere and
the stratosphere)
occurs where the
temperature no
longer decreases.
– Temperatures
increase with
altitude -60oC  0oC

5. The Structure of the
Atmosphere (cont’d)
• Stratosphere
– Contains the ozone
layer (O3) that
reduces the amount
of harmful
ultraviolet radiation.
– Extends from 12 km
to 50 km (7-30
miles).
– Contains 9% of the
atmospheric gases.

6. The Structure of the
Atmosphere (cont’d)
• Mesosphere
– The stratopause
(between the
stratosphere and
mesosphere) occurs
where the
temperature stops
increasing.
– The temperature
decreases with
altitude 0oC  -90oC

7. The Structure of the
Atmosphere (cont’d)
• Mesosphere
–There are very few
gas molecules, so
the pressure is
1/1000th of that at
Earth’s surface.
–Extends from 50
km to 90 km (30-
54 miles).

8. The Structure of the
Atmosphere (cont’d)
• Thermosphere
–The mesopause
(between the
mesosphere and
thermosphere)
occurs where the
temperature stops
going down.

9. The Structure of the
Atmosphere (cont’d)
• Thermosphere
–The
temperature
increases with
altitude -90oC
 unknown
–This is the site
of the Aurora
Borealis

10. Composition of Air and Air
Pressure
• Air contains nitrogen
(78%); Oxygen (21%);
Argon (1%); Carbon
Dioxide (0.03%); and
Neon, Helium, Krypton,
Xenon, and Hydrogen
(trace amounts)
• Water vapor and other
contaminants are not
included in the
composition listed above.

11. Composition of Air and Air
Pressure
• Air pressure is the force
with which a column of air
presses down on Earth’s
surface.
• The average atmospheric
pressure on Earth’s surface
at sea level = 1 atm
(atmosphere).