Composition of the atmosphere

 

Composition of the atmosphere

The air around the Earth is called the atmosphere. It is made of different gases, but it gets thinner as you go higher. The atmosphere does not have a clear end, but some scientists say it stops at about 100 km above the Earth. That is where space starts.

 

 

The air around the Earth has three main gases that are all elements:

 

• Nitrogen (N2) makes up 78% of the air.
• Oxygen (O2) makes up 21% of the air.
• Argon (Ar) makes up 0.9% of the air.

 

These three gases are 99.9% of the air.

The other gases are very small in amount. They include carbon dioxide and water vapour.

 

Living things and the atmosphere

All living things need oxygen from the air to get energy from food. This is called respiration. It happens inside cells, where food and oxygen turn into carbon dioxide and water.

 

The word equation is:

 

Glucose + oxygen → carbon dioxide + water

 

Plants and some bacteria need carbon dioxide from the air to make food. This is called photosynthesis. It happens in green parts of plants, where carbon dioxide and water turn into food and oxygen with light.

 

The word equation is:

 

Carbon dioxide + water → glucose + oxygen

 

You can see that respiration and photosynthesis are opposite. They use each other’s products and make each other’s reactants.

Even plants and animals in the oceans use gases from the air that mix with the water.

 

Combustion and the atmosphere

Combustion is when a fuel burns with oxygen and gives out energy. We burn fuels for many reasons.

 

For example:

 

Cars use petrol or diesel as fuel.

Boilers use natural gas (methane) as fuel to heat water and rooms.

Cookers use natural gas (methane) as fuel to cook food.

Fireplaces use wood, coal or natural gas as fuel to keep warm.

To burn a fuel, you need three things: fuel, heat and oxygen. This is shown by the fire triangle.

 

The fire triangle If you take away any of these things, the fire will stop. Most of the time, the oxygen comes from the air.

 

 

The fire triangle is a symbol that shows the three things that are required for a fire to burn,

Burning fuels makes carbon dioxide. Humans burn a lot of fuels, especially fossil fuels. This adds more carbon dioxide to the air, making the earth’s greenhouse gases thicker. This makes the earth hotter. This is called global warming.

 

Summary:

 

• The air we breathe is a mix of different gases.
• Most of the air is nitrogen (80%) and oxygen (20%). The rest are gases like carbon dioxide and water vapour that are very small in amount.
• Oxygen is essential for all living things to stay alive, and for the combustion (or burning) of fuels.