Life on Earth was anaerobic until oxygen entered the atmosphere about when?

Life on Earth was anaerobic until oxygen entered the atmosphere about when?

Life on Earth was anaerobic until oxygen entered the atmosphere about when?




A. 200 billion years ago
B. 20 billion years ago
C. 2 billion years ago
D. 200 million years ago
E. 20 million years ago
F. 2 million years ago


Answer: C