alleryDuring the Carboniferous period, oxygen reached a peak of about what share?
A10 percent
B21 percent
C35 percent
D50 percent
Answer & Solution
Correct answer: C. 35 percent
1. Oxygen has varied over the last 600 million years.
2. It peaked near 35 percent about 280 million years ago, in the Carboniferous.
3. Today's level is about 21 percent.
_Source: Wikipedia, Atmosphere of Earth, Third atmosphere_
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