Search the Properties of Matter site Properties of Matter glossary Photos, illustrations and streaming media on the Properties of Matter site Properties of Matter table of contents Properties of Matter home page Link to NSRC home page

Reading Selection, Lesson 4

Air Heads

Click here for audio and Spanish translation
What does this explorer have on her mind?
 
What does this explorer have on his mind?

What do these explorers have on their minds?

What do a scuba diver and an astronaut have in common? They both have air on their minds. Air is something most of us take for granted. We might think about it when we are swimming or exercising, but otherwise we know there is plenty of it around. The air that surrounds our entire planet is called the atmosphere. To an astronaut and a diver, air is something to think about. They have to carry an atmosphere with them: their own supply of air compressed into a small tank. If it runs out, they are in big trouble!

Why do we need air? Sometimes people say, “We need air to breathe.” This is the opposite of the truth. In fact, we breathe because we need air—even then, we only need part of it. Air is a mixture of gases. The part we use is called oxygen, and it makes up about one-fifth of normal atmospheric air.

Atmosphere surrounding Earth as seen from space

A layer of air called the atmosphere surrounds Earth.

Why is oxygen so important? Our bodies use oxygen to combine with food substances in a process called respiration. Respiration releases energy that we can then use for our body processes (another gas, carbon dioxide, also found in air, is made in this process). If you were deprived of oxygen for more than a few minutes, these life processes would stop. You would suffocate to death!

Oxygen is also needed for things to burn. Think back to what happened in Lesson 1 when you placed a beaker over a burning candle. The candle went out because it had used up most of the oxygen in the air. Things burn very quickly in pure oxygen. In fact, burning things in pure oxygen can be explosive. It’s a good thing that air consists mainly of another gas called nitrogen.

From our point of view, nitrogen gas doesn’t do very much. Our bodies don’t use it, very few substances react with it, and it’s colorless and odorless.

This 
              fierce 
              forest 
              fire 
              would 
              burn 
              explosively 
              if 
              the 
              atmosphere 
              were 
              pure 
              oxygen. 
              Luckily, 
              air 
              consists 
              mainly 
              of 
              less 
              reactive 
              nitrogen.

This fierce forest fire would burn explosively if the atmosphere were pure oxygen. Luckily, air consists mainly of less reactive nitrogen.

Many of the other gases found in air don’t do much either. Some of these gases, including argon, neon, and helium, are so renowned for doing nothing that they are called inert gases.

Other gases are more important to living things. Without the 0.03 percent of carbon dioxide in the air, there would be no green plants. Plants use carbon dioxide to make food. They use the energy from sunlight to combine water with carbon dioxide to make carbohydrates. They turn parts of the air into living matter! Most plants absorb water through their roots, but water is also found in the air (it’s called water vapor). The amount of water in the form of water vapor varies. On hot, sticky days, you can easily feel that there’s a lot of water in the air.

There are other gases in air. Some of these occur naturally; others are the result of pollution. In fact, air has a chemistry all its own. You will have the opportunity to investigate some aspects of the chemistry of air later in the module.

This 
                  leaf 
                  is 
                  a 
                  factory 
                  that 
                  uses 
                  carbon 
                  dioxide 
                  from 
                  the 
                  air 
                  as 
                  a 
                  raw 
                  material.

This leaf is a factory that uses carbon dioxide from the air as a raw material.

A 
                  simplified 
                  summary 
                  of 
                  the 
                  composition 
                  of 
                  air.

Air is composed of several different gases. This chart provides a simplified summary of the composition of air.

 

 

 

 

 

 


 

QUESTIONS

Use library or Internet resources to answer one of the following questions:

1. Where did Earth’s atmosphere come from?

2. Has the atmosphere always had the same composition?

3. Is the composition of the atmosphere changing? If so, what are the causes of this change? Write your answer as a paragraph with four to seven sentences.

Information about the STC/MS curriculum Link to NSRC home page NSRC contact information NSRC copyright and permissions information Smithsonian Institution privacy policy Properties of Matter site map