The AtmosphereThe Atmosphere

Chapter 18Chapter 18

The atmosphere supports lifeThe atmosphere supports life

Living things occupy only a relative thin Living things occupy only a relative thin layer of the Earth’s crust.layer of the Earth’s crust.– The ocean and the atmosphereThe ocean and the atmosphere

The small fraction of the Earth’s The small fraction of the Earth’s environment that supports life is known as environment that supports life is known as the biosphere.the biosphere.

Subdividing the AtmosphereSubdividing the Atmosphere

The atmosphereThe atmosphere

The atmosphere consists of a mixture of The atmosphere consists of a mixture of gases extending about 100km above the gases extending about 100km above the earth surface.earth surface.

The interactions that occur in the upper The interactions that occur in the upper layers of the atmosphere are mostly layers of the atmosphere are mostly influenced by the high-energy radiation from influenced by the high-energy radiation from the sun. The chemistry of the troposphere, the sun. The chemistry of the troposphere, however, is significantly affected by human however, is significantly affected by human activity on earth.activity on earth.

The atmosphere and radiationThe atmosphere and radiation

High-energy, ultraviolet radiation from the sun is High-energy, ultraviolet radiation from the sun is damaging to living organisms.damaging to living organisms.

Ozone (OOzone (O33) gas can absorb some radiation and ) gas can absorb some radiation and

can act as a protective filter.can act as a protective filter. In the stratosphere, within a band 10-30km above In the stratosphere, within a band 10-30km above

the earth’s surface, is the ozone layer.the earth’s surface, is the ozone layer. This is where ozone occurs at concentrations This is where ozone occurs at concentrations

significantly higher than in the lower regions of the significantly higher than in the lower regions of the atmosphere.atmosphere.

OzoneOzone

In the ozone layer, high-energy UV radiation causes the In the ozone layer, high-energy UV radiation causes the strong double bond of diatomic oxygen molecules (Ostrong double bond of diatomic oxygen molecules (O22) to ) to

break to form highly reactive oxygen atoms:break to form highly reactive oxygen atoms:

Some of these then combine with other oxygen molecules Some of these then combine with other oxygen molecules to form ozone.to form ozone.

O22 O + OUV Radiation

O33O + O22

OzoneOzone

Ozone molecules can also absorb ultraviolet Ozone molecules can also absorb ultraviolet radiation, decomposing to oxygen molecules radiation, decomposing to oxygen molecules and oxygen atoms.and oxygen atoms.

Overall, without human activity, the rate of Overall, without human activity, the rate of formation of ozone is about the same as its formation of ozone is about the same as its rate of depletion, so the concentration of rate of depletion, so the concentration of ozone in the stratosphere remains constant.ozone in the stratosphere remains constant.

O33(g)(g)UV Radiation

O2(g) + O(g)

The atmosphere and climateThe atmosphere and climate

The Earth has maintained its average temperature The Earth has maintained its average temperature over time because of the balance between the over time because of the balance between the radiation received from the sun and that reflected radiation received from the sun and that reflected back into space.back into space.

Radiation of shorter wavelengths can pass Radiation of shorter wavelengths can pass through the atmosphere from the sun, such as through the atmosphere from the sun, such as visible light and UV.visible light and UV.

The earth radiates back lower energy, longer The earth radiates back lower energy, longer wavelength radiation, such as infrared.wavelength radiation, such as infrared.

Gases in the troposphere, such as carbon Gases in the troposphere, such as carbon dioxide, water vapour and methane, absorb dioxide, water vapour and methane, absorb some of the reflected infrared radiation some of the reflected infrared radiation before it can reach space and radiates it before it can reach space and radiates it back to earth as heat. back to earth as heat.

This is known as the greenhouse effect.This is known as the greenhouse effect.

The atmosphere and climateThe atmosphere and climate

The atmosphere and climateThe atmosphere and climate

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Page 316Page 316 Question 1, 3 and 4Question 1, 3 and 4

The atmosphere and essential The atmosphere and essential gases.gases.

Oxygen and Carbon DioxideOxygen and Carbon Dioxide Oxygen makes up 21% of the atmosphere Oxygen makes up 21% of the atmosphere

and is required for respiration.and is required for respiration. Respiration involves glucose and oxygen Respiration involves glucose and oxygen

being broken down into carbon dioxide, being broken down into carbon dioxide, water and energy.water and energy.

Respiration is the major energy-producing Respiration is the major energy-producing process of most living things:process of most living things:

CC66HH1212OO66(aq) + 6O(aq) + 6O22(g) (g) → → 6CO6CO22(g) + 6H(g) + 6H22O(l) + energyO(l) + energy

Oxygen and Carbon DioxideOxygen and Carbon Dioxide

Carbon dioxide makes up only 0.035% of Carbon dioxide makes up only 0.035% of the atmosphere, but provides all food the atmosphere, but provides all food sources on earth.sources on earth.

Photosynthesis is where plants combine Photosynthesis is where plants combine carbon dioxide and water in the presence of carbon dioxide and water in the presence of chlorophyll and sunlight to produce glucose chlorophyll and sunlight to produce glucose and oxygen.and oxygen.

CC66HH1212OO66(aq) + 6O(aq) + 6O22(g)(g)6CO6CO22(g) + 6H(g) + 6H22O(l)O(l)Sunlight

Chlorophyll

Carbon-Oxygen CycleCarbon-Oxygen Cycle

How is Carbon and Oxygen Cycled??

Carbon-Oxygen CycleCarbon-Oxygen Cycle

Both carbon dioxide and oxygen are cycled in the Both carbon dioxide and oxygen are cycled in the processes of photosynthesis and respiration.processes of photosynthesis and respiration.

Carbon dioxide is also returned to the atmosphere Carbon dioxide is also returned to the atmosphere when an organism’s wastes are decomposed.when an organism’s wastes are decomposed.

Volcanic action and combustion of fossil fuels, add Volcanic action and combustion of fossil fuels, add carbon dioxide to the atmospherecarbon dioxide to the atmosphere

The production of coal, oil and natural gas over a The production of coal, oil and natural gas over a period of several million years. This process period of several million years. This process removes carbon from the cycle.removes carbon from the cycle.

NitrogenNitrogen

Nitrogen is essential in DNA and proteins.Nitrogen is essential in DNA and proteins. 78% of the atmosphere is nitrogen but most living 78% of the atmosphere is nitrogen but most living

creatures cannot use it in this form.creatures cannot use it in this form. We depend on a few species of microorganisms We depend on a few species of microorganisms

that can break the strong triple covalent bond that can break the strong triple covalent bond within the nitrogen molecule to form simple within the nitrogen molecule to form simple nitrogen-containing ions such as ammonium or nitrogen-containing ions such as ammonium or nitrate ions.nitrate ions.

Plants can then use these molecules to make Plants can then use these molecules to make more complex nitrogen containing compounds more complex nitrogen containing compounds which us (as animals) can then consume.which us (as animals) can then consume.

NitrogenNitrogen The conversion of atmospheric nitrogen into The conversion of atmospheric nitrogen into

soluble nitrogen compounds that can be soluble nitrogen compounds that can be used by plants is called nitrogen fixation.used by plants is called nitrogen fixation.

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