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The composition of today's atmosphere is primarily characterized by approximately 80% nitrogen and approximately 20% oxygen, along with trace amounts of other gases such as carbon dioxide, argon, and water vapor. This balance between nitrogen and oxygen is essential for maintaining life as we know it, supporting processes such as respiration in animals and photosynthesis in plants.
Nitrogen, being inert, plays a crucial role in stabilizing the atmosphere and preventing rapid chemical reactions, while oxygen is vital for the survival of aerobic organisms. The presence of other gases in trace amounts is also important, even if they are not as abundant. For example, carbon dioxide is integral to the greenhouse effect and photosynthesis, despite making up only a small fraction of the atmosphere.
The options that suggest a much higher percentage of oxygen or a significant imbalance between the gases don't accurately reflect the scientific understanding of atmospheric composition. Thus, the correct answer highlights the accurate proportions that contribute to the overall dynamics of Earth's atmosphere.