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Science that studies the Earth’s
          Evolution of the Earth’s
State Standard #8b
  Students know how the composition of Earth’s atmosphere has
  evolved over geologic time and the effect of out gassing, the
  variations of carbon dioxide concentration, and the origin of
  atmospheric oxygen.
Atmosphere- envelope of gases that surround earth.
  Formation of the Earth’s Atmosphere

First Atmosphere
• Composition - Probably H2, He
• These gases are relatively rare on Earth compared to
  other places in the universe and were probably lost to
  space early in Earth's history because
   – Earth's gravity is not strong enough to hold lighter gases
   – Earth still did not have a differentiated core (solid
     inner/liquid outer core) which creates Earth's magnetic field
     (magnetosphere = Van Allen Belt) which deflects solar winds.
• Once the core differentiated the heavier gases could
  be retained
• The history of the Earth's atmosphere prior to one billion years ago
  is poorly understood, but the following presents a plausible
  sequence of events. This remains an active area of research.
• The modern atmosphere is sometimes referred to as Earth's "third
  atmosphere", in order to distinguish the current chemical
  composition from two notably different previous compositions. The
  original atmosphere was primarily helium and hydrogen; heat (from
  the still molten crust, and the sun) dissipated this atmosphere.
• About 3.5 billion years ago, the surface had cooled enough to form a
  crust, still heavily populated with volcanoes which released steam,
  carbon dioxide, and ammonia. This led to the "second atmosphere";
  which was, primarily, carbon dioxide and water vapor, with some
  nitrogen but virtually no oxygen. (Though very recent simulations run
  at the University of Waterloo and University of Colorado in 2005
  suggested that it may have had up to 40%
  hydrogen.[3] (
  This second atmosphere had ~100 times as much gas as the
  current atmosphere. It is generally believed that the greenhouse
  effect, caused by high levels of carbon dioxide, kept the Earth from
•   During the next few billion years, water vapor condensed to form rain and
    oceans, which began to dissolve carbon dioxide. Approximately 50% of the
    carbon dioxide would be absorbed into the oceans. One of the earliest types
    of bacteria are the cyanobacteria. Fossil evidence indicates that these
    bacteria existed approximately 3.3 billion years ago and were the first
    oxygen producing evolving phototropic organisms. They are responsible for
    the initial conversion of the earth’s atmosphere from an anoxic (state
    without oxygen) to an oxic (with oxygen) state. Being the first to carry out
    oxygenic photosynthesis, they were able to convert carbon dioxide into
    oxygen playing a major role in oxygenating the atmosphere.
•   Photosynthesizing plants would evolve and convert more carbon dioxide
    into oxygen. Over time, excess carbon became locked in fossil fuels,
    sedimentary rocks (notably limestone), and animal shells. As oxygen was
    released, it reacted with ammonia to create nitrogen; in addition, bacteria
    would also convert ammonia into nitrogen.
•   As more plants appeared, the levels of oxygen increased significantly (while
    carbon dioxide levels dropped). At first it combined with various elements
    (such as iron), but eventually oxygen accumulated in the atmosphere —
    resulting in mass extinctions and further evolution. With the appearance of
    an ozone layer (ozone is an allotrope of oxygen) lifeforms were better
    protected from ultraviolet radiation. This oxygen-nitrogen atmosphere is the
    "third atmosphere".
  Formation of the Earth’s Atmosphere
• Second Atmosphere
• Produced by volcanic out gassing.
• Gases produced were probably similar to those
  created by modern volcanoes (H2O, CO2, SO2, CO,
  S2, Cl2, N2, H2) and NH3 (ammonia) and CH4
• No free O2 at this time (not found in volcanic gases).
• Ocean Formation - As the Earth cooled, H2O
  produced by out gassing could exist as liquid in the
  Early Achaean, allowing oceans to form.
   – Evidence - pillow basalts, deep marine seds in
     greenstone belts.
           Atmospheric Out gassing
Out gassing- process by which gases within the Earth were released
  during its formation.
  Formation of the Earth’s Atmosphere
Addition of O2 to the Atmosphere
• Oxygen Production
   – Photochemical dissociation - breakup of water molecules by
        • Produced O2 levels approx. 1-2% current levels
        • At these levels O3 (Ozone) can form to shield Earth
          surface from UV
   – Photosynthesis - CO2 + H2O + sunlight = organic compounds +
      O2 - produced by cyanobacteria, and eventually higher plants
      - supplied the rest of O2 to atmosphere. Thus plant
• Oxygen Consumers
   – Chemical Weathering - through oxidation of surface
      materials (early consumer)
   – Animal Respiration (much later)
   – Burning of Fossil Fuels (much, much later)
  Chapter 22-1 Atmospheric Composition
Purpose of the Atmosphere
   Early Earth would have been very different and inhospitable
   compared to the Earth today.
• Hot
    – Why? - Primordial heat, collisions and compression during
      accretion, decay of short-lived radioactive elements
    – Consequences - Constant volcanism, surface temperature too
      high for liquid water or life as we know it, molten surface or
      thin, unstable basaltic crust.
• Atmosphere - early atmosphere probably completely different in
   composition (H2, He)
• Cooling
    – Primordial heat dissipated to space
    – Condensation of water (rain), accumulation of surface water.
    – Accumulation of new atmosphere due to volcanic out gassing
    – Conditions appropriate for evolution of life
It’s all about chemistry
     Chapter 22-1 Atmospheric Composition
Why the Atmosphere
The atmosphere surrounds Earth and protects us by blocking out dangerous
  rays from the sun. The atmosphere is a mixture of gases that becomes
  thinner until it gradually reaches space. It is composed of Nitrogen (78%),
  Oxygen (21%) and other gases (1%).
  Chapter 22-1 Atmospheric Composition
Nongaseous components of air
   Water vapor- moisture in the air in the form of a gas. Water
   vapor in the air varies from place to place. Water vapor plays a
   very important role in weather.
Particulate matter- tiny particles of dust, smoke, salt, pollen, smog
   and other chemicals.
     Chapter 22.1 Layers of the Earth’s
The atmosphere begins at the earth’s surface and goes more than
  700 km up.
Troposphere- layer of the atmosphere closest to the earth.
       Most water vapor is found here.
       99% of all weather occurs here.
       Temperature drops with altitude.
Stratosphere- second layer of the earth’s atmosphere.
       No weather occurs here.
       Airplanes travel in this layer.
       Strong, dry steady winds.
       Ozone is found here.
Ozonosphere- Layer of the stratosphere that prevents U.V. rays
  from reaching the earth.
Layers of the Earth’s Atmosphere
Atmospheric layers
      Chapter 22.1 Layers of the Earth’s
Mesosphere- Third layer of the earth’s atmosphere.
       Temperatures decrease with an increase in altitude.
        Meteors burn-up
Thermosphere- upper layer of the earth’s atmosphere.
       Temperature increases with an increase in altitude.
        Auroras occur in this region.
Ionosphere- Zone of highly ionized (ions) particles.
       Radio waves can bounce off of this layer.
     Chapter 22.1 What is Air Pressure?
Objective- Explain air pressure and describe what affects it.
  Newton- metric unit of force (f= mass x acceleration)
  Pressure- amount of force per unit of area.
       Weight is a force (mass acted upon by gravity).
       A force exerted over a small area causes more pressure than
  the same force applied over a large area.
Atmospheric Air has weight. 1 L=.01 N @ sea level.
  Pressure is greatest at the Earth’s surface and decreases as altitude
    Factors that affect Atmospheric Pressure
   Air pressure changes with elevation or height above sea level.
        Weight of the air press downward at the surface, forcing
   air molecules close together. Higher up the air molecules are
   further apart creating less pressure.
The higher the elevation, the lower the air pressure.
    Factors that affect Atmospheric Pressure
Water Vapor
   The more water vapor in the air, the lower the air pressure.
Air with a lot of water vapor weights less than dry air. Thus moist
   air exerts less pressure.
Atmospheric Weight (Atomic mass unit)
Nitrogen= 14
Carbon dioxide= 12+16+16=44

  The higher the air temperature, the lower the air pressure.
      Warm air expands and is less dense. (Rising air)
      Cool air contracts and is more dense. (Sinking air)
   Factors that Affect Air Pressure

       Chapter 22.1 How is air pressure
Objective- Explain how a barometer measures air pressure.
  Barometer- instrument used to measure air pressure.
Types of Barometers
Mercury Barometers use a liquid, mercury, to measure air
  pressure. In 1643 Evangelista Torricelli devised the mercury
  barometer. The average sea level column of mercury is 760mm
  or 29.92 in.
                 Types of Barometers
Aneroid barometer do not use liquid. They are constructed with an
  airtight canister. As the canister expands, it indicates a low
  pressure. As the canister contracts, it indicates a high pressure.
       Measurements are recorded in millimeters of mercury
    Units of Measurement of air pressure

All standard measurements are taken at sea level.
 760mm of Mercury
29.92 inches of mercury
1013.2 mb (millibars-metric unit of measurement)
1 inch=34mb
 Measuring Altitude
    Altimeter- device used to measure altitude.
 Chapter 22.2 How is the Earth’s surface
Objective- describe how energy from the Sun warms Earth’s
Radiant energy- energy given off by the Sun that can travel
  through space.
Radiation- movement of the Sun’s energy through space.
The warmth you feel on your skin is radiant energy from the sun.
  The movement of this energy through space is called radiation.
 Chapter 22.2 How is the Earth’s surface
Absorption of Energy
       Dark surfaces absorb light.
       When light is absorbed it usually is changed to heat.
       Light colored surfaces reflect light an stay cool, dark
  colored surfaces absorb light and get warm.
Energy from the Sun
       The Earth receives about 1 billionth of the energy
  that leaves the Sun’s surface.
       Reflected- bounces off the top of clouds.
       Absorbed- water droplets, dust particles absorb the
Atmospheric Heat Budget
          Chapter 22.2 How does heat move
              through the atmosphere?
Objective; Explain how the atmosphere is heated.

Heat moves through the atmosphere in three main ways:

   Conduction- transfer of heat through matter by direct contact.
       transfer of heat energy from one molecule to another molecule.
       Moves from an area of higher temperature to an area of lower

   Convection- process by which heat is transferred through liquids and gases.
        warm air is heated, it expands, it becomes lighter because it is less
   dense and rises.
        cooler air molecules move closer together (contract), become denser
   and sink.
      Energy transfer within the Earth’s
Radiation- Radiant energy is energy emitted from a single source
  (sun) is absorbed and changed into heat energy.
       Radiant energy is short wave energy.
       Heat energy is long wave energy.
       Earth’s surface absorbs energy but reradiates it back into
  the atmosphere, where it is absorbed by atmospheric gases.

Greenhouse Effect- The process where the earth’s atmosphere
  traps earth’s re-radiated energy within the atmosphere,
  warming the earth.
       Chapter 22.3 How do winds form?
Objective- Explain how winds form.
  Wind- horizontal movement of air.
  Air current- up-and-down movement of air.
  Air is free to move in any direction.
  Vertical movement of air is called updrafts or downdrafts.
  Greater volumes of air move horizontally.
  Chapter 22.3 What causes local winds?
Objective- Describe patterns of local winds.
All winds are produced by temperature differences caused by
   unequal heating of the Earth’s surface.
Local wind patterns are small scale winds produced by local changes
   in air pressure.
Sea and Land breezes- produced when land heats up faster than
   water and when land cools off faster than water.

  Sea Breeze                                  Land Breeze
                  Local Wind Patterns
Mountain and Valley Breeze- winds created by differential
  heating of mountains and valleys regions.
Regions of rising air (low pressure), sinking air (high pressure)

        Mountain Breeze                    Valley Breeze
                 Local Wind Patterns

Monsoons- wind that changes direction with the seasons.

        Winter monsoon             Summer monsoon
Cool land surfaces, warm water   Warm land surfaces, cool water
    Chapter 22.3 How is wind measured?

Objective- Explain how weather instruments are used to describe
A wind is named for the direction from which it comes.
  Wind Vane- instrument that indicates wind direction.
Wind sock can indicate direction and speed.
                   Measuring Wind

Anemometer- instrument that measures wind speed.

                            Weather balloons are used to
                            determine wind speed and direction.
                       Wind speed
Wind speed is determined by the velocity that air moves between a
   high and low pressure.
Isobars- line on a weather map that connects equal points of
                       Wind Speed

Pressure Gradient- Rate at which air pressure changes on the
   shortest path between two isobars.

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