6
Study the graph about oxygen content of Earth’s atmosphere.Which describes oxygen content as Earth evolved over time?
Answer
A
Oxygen levels sharply declined about 400 million years ago.B
Oxygen levels stay above 15 percent starting 200 million years agoC
Oxygen levels remain below 5 percent starting 1000 million years ago.D
Oxygen levels raise significantly between 1000 and 700 million years ago.