When did the level of oxygen in Earth's atmosphere become high enough to sustain aerobic respiration?
A) 1.0 billion years ago
B) 1.5 billion years ago
C) 2.7 billion years ago
D) 3.5 billion years ago
Answer: C
Biology & Microbiology
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What will be an ideal response?
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Indicate whether the statement is true or false.
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