To analyze the increase in iron oxide deposits 2.4 billion years ago and 800 million years ago, we should focus on sources of oxygen that would contribute to the formation of these deposits. Here’s an evaluation of each option:
A. Land animals flourished 800 million years ago, releasing oxygen as a byproduct of respiration, which resulted in iron oxide deposits in the rock layers.
This statement is incorrect. Land animals do not produce oxygen during respiration; they consume it for cellular respiration. Therefore, they would not contribute to the formation of iron oxide deposits.
B. Land plants flourished 2.4 billion years ago, giving off oxygen as a byproduct of cellular respiration, which resulted in iron oxide deposits in the rock layers.
This statement is also incorrect. While plants do produce oxygen, 2.4 billion years ago, it was primarily oxygen-producing bacteria that contributed to the oxygen levels, not land plants, as land plants had not yet colonized terrestrial environments.
C. Oxygen-producing bacteria flourished 2.4 billion years ago, giving off oxygen during photosynthesis, which resulted in iron oxide deposits in the rock layers.
This statement is correct. The Great Oxidation Event, which occurred around 2.4 billion years ago, was driven by cyanobacteria that performed photosynthesis and significantly increased the levels of oxygen in the atmosphere, leading to the formation of iron oxides.
D. Bacteria flourished 2.4 billion years ago, removing oxygen from the atmosphere and depositing it in the sediment layers, which resulted in iron oxide deposits in the rock layers.
This statement is incorrect. While certain bacteria can consume oxygen, the increase in iron oxide deposits is associated with an increase in atmospheric oxygen, not its removal.
E. Plants colonized land and flourished beginning 800 million years ago, giving off oxygen as a byproduct of photosynthesis, which resulted in iron oxide deposits in the rock layers.
This statement is correct. The increase in atmospheric oxygen from land plants, which began to significantly flourish around this time, contributed to the formation of iron oxide deposits.
In summary, the correct responses are:
- C. Oxygen-producing bacteria flourished 2.4 billion years ago, giving off oxygen during photosynthesis, which resulted in iron oxide deposits in the rock layers.
- E. Plants colonized land and flourished beginning 800 million years ago, giving off oxygen as a byproduct of photosynthesis, which resulted in iron oxide deposits in the rock layers.
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