The evolution to an oxygen-rich atmosphere:
A)was heavily dependent upon aerobic bacteria.
B)would have occurred even if carbon dioxide had not been present.
C)occurred at the same time the atmospheric levels of carbon dioxide were decreasing.
D)required large amounts of atmospheric nitrogen.

Question

Quizplus · Accepted Answer

The evolution to an oxygen-rich atmosphere occurred as photosynthetic organisms, like cyanobacteria, increased oxygen levels while decreasing carbon dioxide levels through the process of photosynthesis.

The Evolution to an Oxygen-Rich Atmosphere