Our atmosphere
 Earth’s atmosphere = the layer of gases that surround the
 Very thin layer, relative to size of planet
 Atmosphere:
Absorbs solar radiation
Burns up meteors
Transports and recycles water and other chemicals
Moderates climate
Atmospheric composition
78% nitrogen
21% oxygen
1% argon
traces of other permanent gases
and variable small amounts of:
 water vapor
 carbon dioxide
 methane
 pollutants
 etc.
Layers of the Atmosphere
 The atmosphere has four
 Thermosphere
 Mesosphere
 Stratosphere
 Troposphere
Layers of the
The four layers of the atmosphere include:
1. the troposphere, where we live;
2. the stratosphere, which contains the
ozone layer;
3. the mesosphere, where meteors burn; and
4. the thermosphere, where satellites orbit
Layers of the Atmosphere
 The atmosphere is divided into layers based on temperature
5.2 The exosphere and ionosphere
 Communication on Earth depends on
 Satellites transmit information used
for television shows, radio broadcasts,
data and photos used in weather
reports, and long distance telephone
Atmospheric layers
Atmosphere consists of several layers:
• Troposphere = bottom layer, at Earth’s surface; 11 km high;
temperature decreases with altitude
• Stratosphere = next layer up (11–50 km); temperature increases
with altitude; contains “ozone layer”
• Mesosphere = third layer up (50–90 km); temperature decreases
with altitude
• Thermosphere = top layer (90–500 km); very thin air; mostly
lightweight elements; very hot; ionic radiation
Atmospheric layers
Temperature and
vary with
Ozone layer
Tropopause marks
boundary between
troposphere and
stratosphere. Layers
don’t mix.
Ozone layer
 Not really a layer, but a region of higher-than-normal ozone concentrations
(which are still very low)
 ~17–30 km altitude
 Absorbs ultraviolet (UV) radiation from sun, protecting organisms on
surface from radiation damage
Atmospheric properties
 Atmospheric pressure = weight per unit area of air being pulled down
by gravity (is less at higher altitudes)
 Relative humidity = ratio of water vapor air contains relative to how
much it could contain at that temperature
 Temperature = air is warmed by the sun; temperature varies with
altitude, location, time of day
Pressure, density, and altitude
 Gravity pulls most air
molecules close to Earth’s
surface, so air density is
greatest near the surface.
 Atmospheric pressure is the
greatest near the surface
because most molecules are
The sun’s energy heats the
… and does so differentially at different latitudes.
The sun and Earth’s tilt create seasons
The sun drives weather in the
Solar heating
circular currents in
which warm air
rises and cool air
Composition of Atmosphere
(Mixture of gases, solids, and liquids)
 Early atmosphere was much different than today
 Volcanoes produced nitrogen and carbon
dioxide, but little oxygen
 More than 2 billion years ago, early organisms
began producing oxygen
 Eventually, oxygen formed an ozone layer that
protected Earth from harmful rays
 Green plants and diverse life forms developed
Atmospheric Gases
(Mixture of gases, solids, and liquids)
 Nitrogen - 78%
 Oxygen
- 21%
Water Vapor – 0 to 4%
 Used for clouds and precipitation
Carbon Dioxide - .037%
 Keeps Earth warm and is used by plants to
make food
Argon - .93%
Traces of neon, helium, methane, krypton,
xenon, hydrogen, and ozone
Atmospheric Gases
(Mixture of gases, solids, and liquids)
 Atmosphere is changing with the
introduction of pollutants; increasing human
energy use is increasing the amount of
carbon dioxide
 Pollutants mix with oxygen and other
chemicals to form smog
 Aerosols include solids such as dust, salt,
and pollen
 Liquids include water droplets and
droplets from volcanoes
Lower Layers of Atmosphere
 Troposphere: lowest layer – extends up to
10km; contains 99% of the water vapor and
75% of the atmospheric gases
 The troposphere is the first layer above the
surface and contains most clouds and half of
the Earth's atmosphere.
 Weather occurs in this layer.
 Most of the layer’s heat is from Earth
 Temperature cools about 6.5 degrees
Celsius per kilometer of altitude.
Upper Layers of Atmosphere
 Mesosphere – extends from the top of
the stratosphere to about 85 km above
 Coldest layer with little ozone
 Meteors or rock fragments burn up
in the mesosphere.
 Ionosphere here – layer of charged
Upper Layers of Atmosphere
 Thermosphere – thickest atmospheric layer
found between 85 km and 500 km above
Earth’s surface
 The thermosphere is a layer with auroras,
known for its high temperatures.
 Warms as it filters out X-rays and gamma
rays from the Sun
 Ionosphere here, too – help carry radio
The Ionosphere (= Thermosphere)
 Above mesosphere; density so low the Space Shuttle and ISS
orbit here, with little drag
 Temperature can be very high; 4,000F. But no significant heat
because density is so low.
 Heated by ionization by UV from the sun, and the solar
Upper Layers of Atmosphere
 Exosphere - The atmosphere
merges into space in the extremely
thin exosphere. This is the upper
limit of our atmosphere.
 Outer layer where space shuttle
Atmospheric Pressure
 Molecules closer to the surface are
more densely packed (at higher
pressure) together than those
higher in the atmosphere because
of the mass of gases pressing down
on them from higher in the
Temperature in atmospheric layers
 The troposphere is warmed primarily by the
Earth’s surface; temperature decreases as altitude
increases in this layer.
 Temperatures increase as altitude increases in the
stratosphere, particularly in the upper portion –
 Temperatures decrease with altitude in the
 Thermosphere and exosphere are the first to
receive Sun’s rays, so they are very hot
The Ozone Layer
 About 19 km to 48 km above Earth in the stratosphere
(90%) and troposphere (10%).
Layer of 3-atom molecules that protects the Earth from
the Sun’s harmful ultraviolet radiation
Life depends on the ozone!
Pollutants called chlorofluorocarbons (CFCs) are
destroying the ozone
CFCs are used in refrigerators, air conditioners, aerosol
sprays, and foam packaging ~ if products leak, CFCs
enter atmosphere
Ozone layers has a large hole over Antarctica and a
smaller one over the North Pole
The Ozone Layer
Within the stratosphere, about 19 km to 48 km
above your head, lies an atmospheric
layer called the ozone layer.
Ozone is made of oxygen.
Although you cannot see the ozone layer, your
life depends on it.
The Ozone Layer
An ozone molecule is made up of three oxygen atoms bound together.
The ozone layer contains a high concentration of ozone and shields you from
the Sun's harmful energy.
Ozone absorbs most of the ultraviolet radiation that enters the atmosphere.
Ultraviolet radiation is one of the many types of energy that come to Earth
from the Sun.
Evidence exists that some air pollutants are destroying the ozone layer.
Blame has fallen on chlorofluorocarbons (CFCs), chemical compounds used in
some refrigerators, air conditioners, and aerosol sprays, and in the production of some
foam packaging.
When a chlorine atom from a chlorofluorocarbon molecule comes near a molecule of ozone,
the ozone molecule breaks apart.
One of the oxygen atoms combines with the chlorine atom, and the rest form a regular, twoatom molecule.
These compounds don't absorb ultraviolet radiation the way ozone can.
In addition, the original chlorine atom can continue to break apart thousands of
ozone molecules.
The result is that more ultraviolet radiation reaches Earth's surface.
Chlorofluorocarbon molecules destroy ozone.
By October, the ozone concentration reaches its lowest values and then begins to
increase again.
By December, the ozone hole disappears.
The Ozone Hole
The destruction of ozone molecules by CFCs seems to cause a seasonal reduction in ozone
over Antarctica called the ozone hole.
Every year beginning in late August or early September the amount of ozone in the
atmosphere over Antarctica begins to decrease.

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