Which gas is the major component of Earth's atmosphere?

Which gas is the major component of Earth's atmosphere?

• A. Nitrogen
• B. Oxygen
• C. Carbon Dioxide
• D. Argon

Answer: (A)

Think of the atmosphere as being dominated by a single gas. About 78 percent of air is nitrogen, making it the most abundant component. The next major gas is oxygen, at roughly 21 percent, while the remaining small fractions come from argon, carbon dioxide, neon, methane, and other trace gases. Nitrogen leads because of its chemical stability—N2 has a very strong triple bond and is relatively unreactive, so it doesn’t get removed from the air quickly and accumulates over time. Oxygen, though essential for life and constantly cycled through processes like photosynthesis and respiration, remains less abundant than nitrogen. The other gases exist in such tiny amounts that they don’t affect the overall composition much.

Think of the atmosphere as being dominated by a single gas. About 78 percent of air is nitrogen, making it the most abundant component. The next major gas is oxygen, at roughly 21 percent, while the remaining small fractions come from argon, carbon dioxide, neon, methane, and other trace gases. Nitrogen leads because of its chemical stability—N2 has a very strong triple bond and is relatively unreactive, so it doesn’t get removed from the air quickly and accumulates over time. Oxygen, though essential for life and constantly cycled through processes like photosynthesis and respiration, remains less abundant than nitrogen. The other gases exist in such tiny amounts that they don’t affect the overall composition much.