The Earth

1
The Earths Atmosphere

• Michael Beattie

2
Overview

• The Earth is surrounded by a blanket of air,
  which we call the atmosphere.
• It reaches over 640 km from the surface of the
  Earth.
• Almost 99 of the atmosphere lies within 64-80 km
  of the earths surface.
• This thin blanket of air shields the surface and
  its inhabitants from the suns UV radiant energy,
  as well as from material from interplanetary
  space.
• There is no definite upper limit to the
  atmosphere rather, it becomes thinner and
  thinner, eventually merging with the empty space
  that surrounds all the planets.

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Composition of the Atmosphere

• The atmosphere is composed of 78 nitrogen, 21
  oxygen, 0.9 argon, 0.03 carbon dioxide, and
  trace amounts of other gases.
• At the surface there is a balance between usage
  and production of these gases.
• Nitrogen is removed from the atmosphere primarily
  by biological processes that involve soil
  bacteria.
• It is returned mainly through the decaying of
  plant and animal matter.
• Oxygen is removed from the atmosphere during
  breathing, as the lungs take in oxygen and
  release carbon dioxide.
• It is returned during photosynthesis, as plants,
  in the presence of sunlight, combine carbon
  dioxide and water to produce sugar and oxygen.

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Composition of the Atmosphere

• Water vapor is an extremely important gas in our
  atmosphere.
• Its concentration in the atmosphere varies
  greatly from place to place, and from time to
  time.
• Close to the surface in warm, tropical locations,
  water vapor may account for up to 4 of
  atmospheric gases, whereas in colder arctic
  areas, its concentration may dwindle to a mere
  fraction of a percent.
• It forms into cloud particles that grow in size
  and fall to the earth as precipitation.
• It is also provides an important source of
  atmospheric energy in latent heat when it changes
  from vapor into liquid water or ice.
• Latent heat is an important source of energy for
  storms, such as thunderstorms and hurricanes.

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Composition of the Atmosphere

• Carbon dioxide is present as a small but
  important percentage of air (about 0.037).
• It enters the atmosphere mainly from the decay of
  vegetation, but it also comes from volcanic
  eruptions, from the burning of fossil fuels, and
  from deforestation.
• The removal of carbon dioxide from the atmosphere
  takes place during photosynthesis.
• Recent measurements of carbon dioxide show a 15
  increase in the atmospheric concentration since
  1958.
• This increase means carbon dioxide is entering
  the atmosphere at a greater rate than it is being
  removed.
• The increase appears to be due mainly to the
  burning of fossil fuels however, deforestation
  also plays a role.

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Composition of the Atmosphere

• Carbon dioxide like water vapor is a greenhouse
  gas, meaning it traps a portion of the earths
  outgoing energy.
• As the atmospheric concentration of carbon
  dioxide increases, so should the average global
  surface air temperature.
• Most mathematical model experiments that predict
  future atmospheric conditions estimate that
  increasing carbon dioxide levels, along with
  other greenhouse gases, will result in a global
  warming of surface air between 1 and 3.5 degrees
  Celsius by the year 2100.

7
The Early Atmosphere

• The atmosphere that originally surrounded the
  earth was probably much different from the air we
  breathe today.
• The earths first atmosphere, about 4.6 billion
  years ago, most likely consisted of hydrogen and
  helium, the two most abundant gases found in the
  universe.
• Most scientists feel that this early atmosphere
  escaped into space from the earths hot surface.
• A second, more dense atmosphere gradually
  developed as gases from molten rock within the
  earths hot interior escaped through volcanoes
  and steam vents.
• The gases were mostly water vapor (about 80),
  carbon dioxide (about 10) and up to a few
  percent nitrogen.

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The Early Atmosphere

• Oxygen began an extremely slow increase in
  concentration as rays from the sun split water
  vapor into hydrogen and oxygen.
• The hydrogen, being lighter, probably rose and
  escaped into space, while the oxygen remained in
  the atmosphere.
• This slow increase in oxygen may have provided
  enough of this gas for primitive plants to
  evolve, and as plant growth increased our
  atmosphere was greatly enriched with oxygen.

9
Air Density and Pressure

• Air density is greatest at the surface and
  decreases as we move up into the atmosphere
  rapidly at first, then more slowly as we move
  farther from the surface.
• The weight of all the air around the earth is
  5600 trillion tons.
• Atmospheric pressure always decreases with
  increasing height.
• Normal atmospheric pressure near sea level is
  1013.25 mb or 14.7 pounds per square inch.

10
Layers of the Atmosphere

• Troposphere The troposphere is the lowest region
  in the earth's atmosphere. On the earth, it goes
  from ground level up to about 17 kilometers high.
  The weather and clouds occur in the troposphere.
  In the troposphere, the temperature generally
  decreases as altitude increases.
• Tropopause The tropopause is the boundary zone
  (or transition layer) between the troposphere and
  the stratosphere. The tropopause is characterized
  by little or no change in temperature as altitude
  increases.
• Stratosphere The stratosphere is characterized
  by a slight temperature increase with altitude
  and the absence of clouds. The stratosphere
  extends between 17 to 50 kilometers above the
  earth's surface. The earth's ozone layer is
  located in the stratosphere. Ozone, a form of
  oxygen, is crucial to our survival this layer
  absorbs a lot of ultraviolet solar energy.

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Layers of the Atmosphere

• Mesosphere The mesosphere is characterized by
  temperatures that quickly decrease as height
  increases. The mesosphere extends from between 50
  and 80 kilometers above the earth's surface.
• Ionosphere The ionosphere starts at about 70-80
  km high and continues for hundreds of kilometers
  (about 640 km). It contains many ions and free
  electrons (plasma). The ions are created when
  sunlight hits atoms and tears off some electrons.
  Auroras occur in the ionosphere.
• Thermosphere The hot layer above the mesosphere.
  In the thermosphere there are relatively few
  atoms and molecules. Consequently, the absorption
  of a small amount of solar energy can cause a
  large increase in air temperature that my exceed
  500 degrees Celsius.
• Exosphere The exosphere is the outermost layer
  of the Earth's atmosphere. The exosphere goes
  from about 640 km high to about 1,280 km. The
  lower boundary of the exosphere is called the
  critical level of escape, where atmospheric
  pressure is very low (the gas atoms are very
  widely spaced) and the temperature is very low.

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