What is the primary composition of Earth's atmosphere in terms of nitrogen and oxygen?

The primary composition of Earth's atmosphere is indeed approximately 78% nitrogen and 21% oxygen. This balance is essential for sustaining life, as nitrogen acts as a stable, inert gas that contributes to the overall pressure of the atmosphere without participating directly in life processes. On the other hand, oxygen is crucial for respiration in aerobic organisms and is involved in various chemical reactions, including combustion.

Understanding this composition is fundamental in fields such as aerospace physiology, where the effects of different atmospheric compositions on human physiology in flight environments are studied. The percentages given reflect the commonly accepted measurements of atmospheric gases at sea level, underscoring the importance of this ratio for both ecological balance and human health during flights.