Oxygen did not accumulate in the early atmosphere until it reacted with reduced materials, especially ________, in the oceans.
A. hydrogen
B. elemental sulfur
C. ferrous iron
D. nitrate
Answer:C
Oxygen did not accumulate in the early atmosphere until it reacted with reduced materials, especially ________, in the oceans.
A. hydrogen B. elemental sulfur C. ferrous iron D. nitrate