RAS question
Earth's atmosphere is composed primarily of:
Correct answer: (D) Nitrogen (78%) and Oxygen (21%).
Earth's atmosphere is composed primarily of nitrogen at about 78% and oxygen at about 21%.
Explanation
NASA states that near Earth's surface, the atmosphere consists of 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon. Nitrogen is the dominant gas, while oxygen is the second-largest component. The standard finer values are nitrogen about 78.09%, oxygen about 20.95%, argon about 0.93%, and carbon dioxide about 0.04%, with trace gases such as neon, helium, methane, and krypton. Hydrogen and carbon dioxide do not make up 78% of the air, and oxygen-nitrogen reversal gives the wrong composition.
Why the other options are wrong
- (A) Hydrogen is not the main gas in Earth's atmosphere; nitrogen is the roughly 78% component.
- (B) Carbon dioxide is only part of the small 'other gases' fraction, not 78% of the atmosphere.
- (C) This pairing reverses the two major gases: oxygen is about 21%, while nitrogen is about 78%.
Concept
Atmospheric composition is a core physical geography fact used in climate, weather, and environmental questions. It recurs in RAS because gas composition links directly to greenhouse gases, atmospheric layers, and human-environment interactions.