Multiple Choice
How does the fraction of oxygen in Earth's atmosphere today compare to what it was 3 billion years ago?
A) It has significantly declined.
B) It has significantly increased.
C) It increased up to 2 billion years ago but has been declining ever since.
D) It declined up to 2 billion years ago but has been increasing ever since.
E) It hasn't changed.
Correct Answer:
Verified
Correct Answer:
Verified
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