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7/27/2019 The Atmosphere - Ch 18
http://slidepdf.com/reader/full/the-atmosphere-ch-18 1/19
The Atmosphere
Chapter 18
7/27/2019 The Atmosphere - Ch 18
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The atmosphere supports life
Living things occupy only a relative thin
layer of the Earth’s crust.
– The ocean and the atmosphere
The small fraction of the Earth’s
environment that supports life is known as
the biosphere.
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Subdividing the Atmosphere
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The atmosphere
The atmosphere consists of a mixture of gases extending about 100km above theearth surface.
The interactions that occur in the upper layers of the atmosphere are mostlyinfluenced by the high-energy radiation from
the sun. The chemistry of the troposphere,however, is significantly affected by humanactivity on earth.
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The atmosphere and radiation
High-energy, ultraviolet radiation from the sun is
damaging to living organisms.
Ozone (O3) gas can absorb some radiation and
can act as a protective filter.
In the stratosphere, within a band 10-30km above
the earth’s surface, is the ozone layer.
This is where ozone occurs at concentrationssignificantly higher than in the lower regions of the
atmosphere.
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Ozone
In the ozone layer, high-energy UV radiation causes the
strong double bond of diatomic oxygen molecules (O2) to
break to form highly reactive oxygen atoms:
Some of these then combine with other oxygen molecules
to form ozone.
O2 O + OUV Radiation
O3O + O2
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Ozone
Ozone molecules can also absorb ultravioletradiation, decomposing to oxygen moleculesand oxygen atoms.
Overall, without human activity, the rate of
formation of ozone is about the same as itsrate of depletion, so the concentration of ozone in the stratosphere remains constant.
O3(g)UV Radiation
O2(g) + O(g)
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The atmosphere and climate
The Earth has maintained its average temperature
over time because of the balance between the
radiation received from the sun and that reflected
back into space. Radiation of shorter wavelengths can pass
through the atmosphere from the sun, such as
visible light and UV.
The earth radiates back lower energy, longer
wavelength radiation, such as infrared.
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Gases in the troposphere, such as carbon
dioxide, water vapour and methane, absorb
some of the reflected infrared radiation
before it can reach space and radiates it
back to earth as heat.
This is known as the greenhouse effect.
The atmosphere and climate
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The atmosphere and climate
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Your Turn
Page 316
Question 1, 3 and 4
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The atmosphere and essential
gases.
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Oxygen and Carbon Dioxide
Oxygen makes up 21% of the atmosphereand is required for respiration.
Respiration involves glucose and oxygen
being broken down into carbon dioxide,water and energy.
Respiration is the major energy-producing
process of most living things:
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + energy
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Oxygen and Carbon Dioxide
Carbon dioxide makes up only 0.035% of
the atmosphere, but provides all food
sources on earth.
Photosynthesis is where plants combine
carbon dioxide and water in the presence of
chlorophyll and sunlight to produce glucose
and oxygen.
C6H12O6(aq) + 6O2(g)6CO2(g) + 6H2O(l)Sunlight
Chlorophyll
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Carbon-Oxygen Cycle
How is Carbon and Oxygen Cycled??
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Carbon-Oxygen Cycle
Both carbon dioxide and oxygen are cycled in the
processes of photosynthesis and respiration.
Carbon dioxide is also returned to the atmosphere
when an organism’s wastes are decomposed.
Volcanic action and combustion of fossil fuels, add
carbon dioxide to the atmosphere
The production of coal, oil and natural gas over aperiod of several million years. This process
removes carbon from the cycle.
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Nitrogen
Nitrogen is essential in DNA and proteins.
78% of the atmosphere is nitrogen but most livingcreatures cannot use it in this form.
We depend on a few species of microorganismsthat can break the strong triple covalent bondwithin the nitrogen molecule to form simplenitrogen-containing ions such as ammonium or nitrate ions.
Plants can then use these molecules to makemore complex nitrogen containing compoundswhich us (as animals) can then consume.
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Nitrogen
The conversion of atmospheric nitrogen intosoluble nitrogen compounds that can be
used by plants is called nitrogen fixation.