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Question
The term reducing atmosphere for the early Earth means that the atmosphere ______.
Options
was much thinner around the surface of the earth than now
contained only two or three kinds of gases
contained little or no free oxygen
contained little or no free nitrogen
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Solution
The term reducing atmosphere for the early Earth means that the atmosphere contained little or no free oxygen.
Explanation:
The primitive atmosphere of the Earth was reducing, meaning it had abundant hydrogen, nitrogen, carbon dioxide, methane, ammonia, and water vapor, but lacked free oxygen. This lack of free oxygen prevented oxidation reactions, allowing complex organic molecules to form and accumulate without being destroyed. The atmosphere shifted from reducing to oxidizing only after photosynthetic organisms started releasing oxygen into the atmosphere.
