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The Atmosphere

Chapter 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.

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Your Turn

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Questions 5 - 8