What are the two most abundant gases in Earth's atmosphere?

• A. Nitrogen and Oxygen
• B. Carbon Dioxide and Methane
• C. Argon and Neon
• D. Water Vapour and Ozone

Answer: (A)

The atmosphere’s main composition is built around two gases that dominate by volume. Roughly three quarters of dry air is nitrogen, and about one fifth is oxygen, making them the two most abundant gases overall. Nitrogen is so plentiful because it is chemically quite inert, so it isn’t easily removed once it’s outgassed from Earth's interior. Oxygen comes from photosynthesis by plants and microscopic organisms, which continually replenishes it even though some of it is consumed by respiration and oxidation. The leftovers—carbon dioxide, neon, argon, methane, and others—exist in much smaller amounts, and water vapor and ozone can vary a lot with location and weather but are still far less abundant on average than nitrogen and oxygen.