What is in the air

The idea

The atmosphere, held in place by Earth's gravity, is mainly nitrogen (78%) and oxygen (21%), with small amounts of argon, carbon dioxide, water vapour and other gases.

A breath of air

You breathe air all day. It looks like nothing.

Which gas makes up the largest share of air?

• Nitrogen
• Oxygen
• Carbon dioxide

Air and its gases

Press Next step.

Mostly two gases

Most of the air is nitrogen and oxygen. The rest is small amounts of other gases. Gravity keeps them close to the Earth.

The atmosphere, held in place by Earth's gravity, is mainly nitrogen (78%) and oxygen (21%), with small amounts of argon, carbon dioxide, water vapour and other gases.

Notes

The atmosphere is held by gravity and is mainly nitrogen (78%) and oxygen (21%), with small amounts of other gases.

Check yourself

Which gas makes up the largest part of the atmosphere?

What is the share of oxygen in the atmosphere?

What holds the atmosphere in place around the Earth?

Nitrogen is 78% and oxygen is 21% of the atmosphere. Together, what percentage of the atmosphere are they?

Answer: 99 %

• Oxygen. Oxygen is 21% of the atmosphere, nitrogen is 78%.
• Carbon dioxide. Carbon dioxide is one of the small amounts of other gases.
• Nitrogen — correct. Yes!
• 21% — correct. Yes!
• 78%. 78% is the share of nitrogen.
• 1%. The share of oxygen is 21%. Small amounts of argon, carbon dioxide, water vapour and other gases are the rest.
• The Sun's heat. The chapter says the atmosphere is held in place by the Earth's gravity.
• The force of the Earth's gravity — correct. Yes!
• The ozone layer. The ozone layer absorbs UV. It is gravity that holds the atmosphere in place.