Earth’s Atmosphere
Part 1 - A view of Planet Earth:
Spheres Within a Sphere
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The Size of the Earth
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Diameter (N to S): 12,740 km
Circumference (distance
around the Earth) at the
equator: 40,075 km
Equator: imaginary line around
the Earth that divides Earth
into two hemispheres,
Northern and Southern
Hemisphere = half a sphere
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Three Main Features of the Earth
Lithosphere:
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All the land on Earth
the crust
Includes the continents and
all the land beneath the
oceans and the continents
Atmosphere:
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Envelope of gases that
surrounds the Earth
Provides materials
necessary to support life
Protects the Earth
Hydrosphere:
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All the water on Earth
Includes oceans, rivers,
streams, lakes, ponds, etc.,
the water frozen in glaciers
and at the poles, and water
in underground aquifers
97% is salt water
85% of the fresh water is
frozen in the polar ice caps
leaving only 15% of the 3%
available for use
Earth’s Atmosphere
Part 2 – Development of the Atmosphere
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The Past Atmosphere
Theory: 4 billion years ago
the atmosphere contained
two deadly gases, methane
(CH4) and ammonia (NH3),
and also some water
Sunlight triggered chemical
reactions forming new
materials: nitrogen, hydrogen,
and carbon dioxide.
Methane and ammonia were
removed but water
remained.
The hydrogen dissipated into
space.
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The Past Atmosphere
When cyanobacteria evolved
they began releasing oxygen
into the atmosphere as a byproduct of photosynthesis.
Some O2 molecules rose to
the stratosphere where
sunlight caused them to be
converted into ozone (O3).
The ozone layer (at 30km
above the Earth’s surface)
protects life on Earth by
absorbing most of the
harmful UV radiation from
the sun.
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The Past Atmosphere
In time, green algae and
plants also began to
release oxygen into the
atmosphere.
Around 600 million years
ago the amounts of
oxygen and carbon
dioxide stabilized to their
present levels.
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The Present Atmosphere
Composition of dry atmosphere:
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Nitrogen ~ 78%
Oxygen ~ 21%
Argon ~ .9%
All other gases, including the
greenhouse gases carbon dioxide
and methane, <0.04%
Water Vapor
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~0.40% over full atmosphere
typically 1% – 4% at surface
The Present Atmosphere
In addition to all the gases
that make up the
atmosphere there are also
tiny particles of solid
materials.
These may include dust,
smoke, dirt, and bits of salt.
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Mold spores and pollen can
also be found at varying
levels through the year.
Sources may be natural
(volcanoes for example) or
artificial (industrial
pollutants).
Oxygen
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Used by all organisms that
carry out aerobic
respiration.
Released by plants as they
carry out photosynthesis.
Also needed in order for
things to burn
(combustion) and rust
(oxidation).
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Oxygen does cycle in and
out of the atmosphere,
but it is not a limiting
factor for the growth of
organisms, nor are high
levels a concern.
Atmospheric Cycles
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Cycles are used by scientists to describe how substances
naturally enter and leave the atmosphere.
Three cycles that are important to organisms are:
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The Nitrogen Cycle
The Carbon Cycle
The Water Cycle
Nitrogen
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View the following animation on the Nitrogen Cycle:
http://moodle.oakland.k12.mi.us/os/mod/page/view.php?id=37546
&inpopup=1
Major Points to the Nitrogen Cycle:
 All living things need nitrogen to make proteins and nucleic
acids (DNA and RNA).
 N2 gas in the atmosphere can’t be used by most organisms.
 Certain bacteria that live in symbiotic relationships with
plants, or that live in the soil, can “fix” N2, converting it into
NH3 that can be used by plants or be converted to NO3
that can be used. (= nitrogen fixation)
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Nitrogen
Major Points to the Nitrogen Cycle (continued):
 Animals get nitrogen by eating plants, or other animals
 When organisms die and their bodies decompose, most of
the organic compounds are changed back into inorganic
compounds, including NH3, NO3, and NO2. These
compounds can then be taken up by plants and reused.
 Certain bacteria in the soil change some of these
compounds back into nitrogen gas (N2) that is released
back into the atmosphere. (= denitrification)
FYI: In an energy consuming process, humans artificially
convert N2 into NH3 and NO3 to make fertilizer. Overuse of
fertilizer can alter the natural nitrogen cycle and change the
growth of organisms in an area.
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Assignment
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Working with a partner, create a labeled diagram of the
nitrogen cycle.
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Use your notes about the major points to the nitrogen cycle as
a guide for what to include.
Use arrows to show the direction of movement of nitrogen.
Use illustrations where helpful.
The Nitrogen Cycle
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Carbon
View the following animation on the carbon cycle:
http://moodle.oakland.k12.mi.us/os/mod/page/view.php?id=37546
&inpopup=1
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Major Points to the Carbon Cycle
 Present as carbon dioxide in the atmosphere
 Used by plants to make organic compounds during
photosynthesis
 Absorbed by ocean waters, where it is used by phytoplankton
for photosynthesis
 Produced by all organisms during the process of respiration
(including water dwellers)
 Released when organic compounds decompose or are burned
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Assignment
Working with a partner, create a labeled diagram of the
carbon cycle.
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Use your notes about the major points to the carbon cycle as
a guide for what to include.
Use arrows to show the direction of movement of carbon.
Use illustrations where helpful.
THE CARBON CYCLE: This diagram of the fast carbon cycle shows the movement of
carbon between land, atmosphere, and oceans.Yellow numbers are natural fluxes, and red are
human contributions in gigatons of carbon per year. White numbers indicate stored carbon.
(Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)
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Water
View the following animation on the water or hydrological
cycle:
http://moodle.oakland.k12.mi.us/os/mod/page/view.php?id=375
46&inpopup=1
Major Points to the Water Cycle
 The evaporation and precipitation of water drive the cycling of
water across the Earth.
 The most evaporation occurs over the ocean.
 Most water evaporated from the ocean forms clouds
(condensation) and then precipitates back into the ocean.
 Some water vapor is blown over land where it then condenses
into clouds and precipitates on to the land.
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Water
Major Points to the Water Cycle…continued
 Evaporation also occurs from lakes and rivers and from
the soil.
 Plants also release water into the air by transpiration (the
evaporation of water taken up by roots and transported
to the leaves).
 Some water that precipitates is absorbed by the ground
and can be used by plants. Some becomes runoff and
flows into streams, rivers, ponds, and lakes.
 Some water eventually flows back to the oceans.
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Assignment
Working with a partner, create a labeled diagram of the
water cycle.
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Use your notes about the major points to the water cycle as
a guide for what to include.
Use arrows to show the direction of movement of water.
Use the appropriate labels for each part of the cycle.
Use illustrations where helpful.
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