The Earth's atmosphere is made up of the following gases: 

Nitrogen: 78%

Oxygen: 21%

Argon: 0.9%

Carbon dioxide: 0.04%

Water vapor: About 0.4% on average, but varies from place to place and time to time

Other gases: Trace amounts of methane, neon, and other gases make up the remaining 0.1%

Explanation

Nitrogen: The most abundant gas in the Earth's atmosphere 

Oxygen: An important gas for humans and other living beings, and is essential for respiration 

Carbon dioxide: A heat-trapping greenhouse gas that contributes to global warming 

Water vapor: The gas phase of water, which enters the atmosphere through evaporation 

The amount of carbon dioxide in the atmosphere is increasing due to the burning of fossil fuels. Humans, other animals, and plants add carbon dioxide to the air through respiration. Plants use carbon dioxide during photosynthesis to make food and oxygen.