The Atmosphere

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					             The Atmosphere
I. The Earth’s Atmosphere is a layer of air surrounding the Earth
that supports and protects life by:
          1. Absorbing harmful radiation
          2. Maintaining the Earth’s temperature
          3. Providing elements essential for life

     A. Our atmosphere is a mixture of gasses that is held around the
        planet by gravity.

     B. The atmosphere has both physical and chemical properties.
         1. Density (physical property)
              - density of the atmosphere decreases with altitude
         2. Composition (chemical property)

                                       - 78.08% Nitrogen
                                       - 20.94% Oxygen
                                       - 0.93% Argon
                                       - 0.04% Carbon Dioxide
                                       - 0.01% Other Elements
                                       - 0-4% Water Vapor



II. Natural processes modify the atmosphere

                                             A. Carbon Cycle
                                       Plants take in carbon
                                       dioxide from the air and
                                       release oxygen during
                                       photosynthesis. During
                                       respiration, animals use
                                       oxygen and release carbon
                                       dioxide and water into the
                                       air.
                                 B. Nitrogen Cycle
                           Nitrogen-fixing bacteria convert
                           atmospheric nitrogen into solid forms
                           and solutions. Living things use these
                           forms of nitrogen, and when they
                           decay, they release nitrogen back into
                           the soil and eventually back into the
                           air.

                                      C. Water Cycle
                                      Water is constantly
                                      circulated between Earth’s
                                      surface and the atmosphere
                                      by evaporation, condensation,
                                      and precipitation.

III. Energy from the Sun heats the atmosphere.
    A. Most energy on Earth comes from the Sun in the form of visible
       light.
    B. Visible light is a form a radiation that moves in electromagnetic
       waves.
              - 30% of the sun’s radiation is reflected by clouds, the
                     atmosphere, and Earth’s surface.
              - 70% of solar radiation is absorbed and becomes
                     different forms of energy.

IV. The atmosphere moves energy by radiation, conduction, and
convection.
    A. Radiation
         1. Energy in the form of electromagnetic waves
         2. Energy hits a surface, it heats the surface
         3. Causes the molecules to move faster you feel this as an
            increase in temperature
         4. The energy on the surface is then transferred to the
            atmosphere

    B. Conduction
         1. The transfer of thermal energy from one material to
            another by direct contact.
         2. Thermal energy is always transferred from warm to cold
            objects
         3. Warm land or water will heat the air on the surface

    C. Convection
         1. The transfer of thermal energy by circulation or
            movement of a liquid or gas
         2. Warm air is less dense and rises, Cool air is more dense
            and sinks
         3. Cooler air is heated by the ground and rising air loses heat
         4. This circular movement of the air is called a convection
            current

V. The Atmosphere can be divided into 4 different layers.
Layer 1 – Troposphere
         about 0-10 km (0-6 miles) above the Earth’s surface

         most clouds and weather located in this layer

         water vapor and dust can also be found in this layer

         WE live in this layer of the atmosphere

         this layer contains 80% of the total mass of the atmosphere

         in this layer, temperature decreases as altitude (height above

           the Earth’s surface) increases

Layer 2 – Stratosphere
         about 10-50 km (6-31 miles) above the Earth’s surface

         hardly any water vapor or dust in this layer because there is

           very little mixing with the air below.
         the air is “thinner” here; it contains less molecules

         this layer contains the ozone layer

         because ozone absorbs the ultraviolet light from the sun, this

           layer gets warmer as the altitude increases

Layer 3 – Mesosphere
         about 50-90 km (31-56 miles) above the Earth’s surface

         in this layer temperature falls as altitude increases

         this is the coldest part of the atmosphere temperatures

           recorded at -93C
         violent wind storms occur in this layer with winds reaching

           320 km/h
         we have not had any aircraft reach this layer only very large

           helium balloons reach this high

Layer 4 – Thermosphere
         about 90 km and up (50 miles and above)

         where nitrogen and oxygen absorb solar energy like x-rays

           and gamma rays
         temperature increasing

         gas particles become electrically charged and can radiate

           energy as light (ex. Aurora Borealis-northern lights and
           Aurora Australis-southern lights)
         this layer can reflect radio waves
   Some scientists describe a 5th layer as the Exosphere.

   Once we get above 180 miles above the surface of the Earth, the
   atmosphere gradually merges with the thin gasses of interplanetary
   space. Remember there is not a line or an edge to our atmosphere; it
   slowly ends and blends into space.

   VI. Gases in the atmosphere absorb radiation.

        A. Gasses can absorb and give off radiation.
             1. In the stratosphere, ozone gas absorbs ultraviolet
                radiation.
             2. In the troposphere, Carbon Dioxide, Methane, Water
                Vapor, and Nitrous Oxide absorb and emit infrared
                radiation.

        B. The ozone layer protects life from harmful radiation by
           absorbing ultraviolet (UV) rays.
             1. Ozone is a gas made up of 3 bonded oxygen atoms – O3
             2. UV rays can cause sunburn, skin cancer, & damaged
                eyesight.

        C. The greenhouse effect keeps the Earth warm.
             1. Water vapor, carbon dioxide, methane, nitrous oxide, and
                 some other gasses are known as green house gasses.
             2. These gasses absorb and give off infrared radiation
                 through a process called the Greenhouse Effect.

GREENHOUSE EFFECT:
                           Solar Radiation heats Earth’s surface, which
                            grows warm and emits infrared radiation.
                           Greenhouse gasses absorb some of this
                            infrared radiation and allow the rest to pass
                            into space.
                           Greenhouse gasses then emit infrared
                            radiation. Some is absorbed by the ground,
                            while some is lost to space.
VII. Human Activities affect the atmosphere.
  A. Human activity can cause air pollution.
      1. Air Pollution consists of gases and particulates.
             a. Gases include: methane, ozone, carbon monoxide,
                sulfur oxides, & nitrogen oxides.
             b. Particulates include: dust, dirt, pollen, and sea
                salt.
       2. Air pollution can be caused naturally (volcanoes) or by
          human activities (burning fossil fuels).

  B. Human activities are increasing greenhouse gasses.
       1. When greenhouse gasses increase, global temperatures
          increase.
       2. Increased greenhouse gasses may lead to global
          warming or global climate change.

   C. Human activities produce chemicals that destroy the ozone
      layer.
        1. Chlorofluorocarbons (CFCs) are chemicals that were
           once used in cooling systems, spray cans, and foam
           packing that react with sunlight and destroy ozone
           molecules. Substitute chemicals that destroy ozone
           more slowly are now used.

        2. Chemical reactions in the stratosphere that produce
           and destroy ozone depend on the weather. Much of the
           ozone over the South Pole is destroyed in certain
           seasons, resulting in the “Ozone Hole”.