Two competing models describe the Earth's early atmosphere. Model 1 suggests a 'reducing' atmosphere, rich in hydrogen, methane, and ammonia, consistent with the conditions for abiotic synthesis of organic molecules (e.g., Miller-Urey experiment). Model 2 proposes a 'neutral' atmosphere, composed mainly of nitrogen, carbon dioxide, and water vapor, with little free hydrogen, based on volcanic gas compositions.
If geological evidence from ancient rocks revealed extensive deposits of oxidized iron formations from the early Earth, this would most strongly support which model?
Correct: B
Model 1 suggests a 'reducing' atmosphere, which would have very little or no free oxygen. The presence of 'oxidized iron formations' (like Banded Iron Formations) requires an oxidizing agent, typically free oxygen. Therefore, extensive deposits of oxidized iron from the early Earth would directly contradict a 'reducing' atmosphere and instead suggest the presence of some oxidizing agent, which is more consistent with, or at least not contradicted by, a 'neutral' atmosphere that could eventually lead to oxygen accumulation, as opposed to a strongly reducing one. Thus, it would most strongly support Model 2, or at least weaken Model 1's claims about a strongly reducing early Earth.