Which organism would be most affected by the absence of the atmosphere?

• A. Humans
• B. Volcanoes
• C. Plants
• D. Fish

Answer: (D)

Without air, there’s no oxygen to breathe and no air pressure to keep environments stable. The immediate consequence for life is the loss of the primary gas exchange with the atmosphere. Among the options, organisms living in water would be hit the hardest because they rely on dissolved oxygen in the water, which depends on contact with the air above. If the atmosphere vanishes, the amount of oxygen that can dissolve into water drops quickly and cannot be replenished, so aquatic animals like fish would suffocate rapidly. Plants would also suffer because they rely on carbon dioxide for photosynthesis, and a vanished atmosphere removes a major CO2 source; however, some CO2 remains in water and aquatic plants can often use that, at least for a time. Humans and other air-breathing land animals depend on atmospheric oxygen and would be affected, but the immediate and severe disruption to the oxygen supply in water makes fish the most affected in this scenario.