The planet Earth is covered by a thick “blanket” of gases that is called the atmosphere. The thickness of the layer (atmosphere) in relation to the size of the earth can be compared to the thickness of the peel of an orange in relation to the size of the orange.

Figure 1

Life on earth would not be possible without the atmosphere. The atmosphere does not only consist of gases that are essential for life, but it also prevents us from being ‘roasted’ by the sun and from being frozen to death by the extreme cold of outer space. The atmosphere allows only half of the rays of the sun to reach the earth’s surface.

The atmosphere has four layers .

Figure 2

Layer 1: The Troposphere

This is the layer that is right against the surface of the earth. It is about 11 km thick and it is in this layer that weather changes take place in the air. It is practically only in this layer that water is found.

The air in the troposphere consists mainly of two gases: nitrogen and oxygen. There is a very small amount of other gases.

You can illustrate the composition of the air with balloons:

Figure 3

Count the balloons and write down the numbers:

Those with an N (that is for nitrogen):

Those with an O (that is for oxygen):

Those with an OG (that is for other gases):

Now describe in your own words how the air is composed in the troposphere (the air that we breathe):

The higher one moves up into the troposphere, the “thinner” the air gets. That means that the particles are spread out so that they are further away from each other. For example, if you were to fill a container with air at an altitude of 8 km, there would be fewer particles (nitrogen, oxygen and other gases) in the container than if you were to fill the container on ground level.

Layer 2: The Stratosphere

The stratosphere is approximately 40 km thick. Aircraft fly in this layer. The very important ozone layer is found in the stratosphere. The ozone layer is a kind of oxygen layer that protects the earth against the harmful rays of the sun. Without this layer most living creatures on earth would die. The oxygen in the ozone layer comes from the plants that grow on earth. If this balance were to be disturbed because less oxygen were to reach the ozone layer and its place were to be taken up by other gases that are released by certain human activities, it would alter the temperature on earth. That could ultimately mean that both animal and plant life would become impossible. Plants and animals would be wiped out.

Layer 3: the mesosphere

This layer is approximately 40 km thick and is characterised by fluctuations in temperature between -113° Celsius and 440° Celsius. (One’s body temperature is 37° Celsius, water freezes at approximately 0° Celsius and boils at approximately 100° Celsius.) Rocks that fall from outer space are incinerated in this layer and we see them as “falling stars”.

Layer 4: The Ionosphere (thermosphere)

The ionosphere layer is about 350 km thick and contains many charged particles (ions). They deactivate a great deal of the radioactivity that is caused by the sun at certain times, so that it does not have any effect on the earth.

Questions:

1. Why is it always important that we plant more plants instead of destroying them?

2. Industrial progress can be harmful to nature because it can change the atmosphere. Explain why.

3. Why do mountaineers who climb high mountains such as Everest, wear oxygen masks?

LEARNING OUTCOME 2: CONSTRUCTION OF SCIENTIFIC KNOWLEDGE

Learners know, interpret and apply scientific, technological and environmental knowledge.

We know this when the learner:

2.1 recalls significant information;

2.2 categorises information.

Number of balloons (but let the learners count first):

N 79

O 20

OG 1

Composition: In every 100 parts there are 79 parts nitrogen (79 %), 20 parts oxygen (20 %) and one part other gases (1 %)

Answers:

N.B.: These questions must be answered with specific reference to the atmosphere.

3. The pressure becomes so low that there is too little oxygen per volume unit.