Question

which describes oxygen content as earth evolved over time? oxygen levels sharply declined about 400 million years ago. oxygen levels stay above 15 percent starting 200 million years ago oxygen levels remain below 5 percent starting 1000 million years ago. oxygen levels raise significantly between 1000 and 700 million years ago.

Explanation:

By observing the graph, oxygen levels were below 5 percent from 1000 million years ago until around 600 - 700 million years ago. There is no sharp decline around 400 million years ago, oxygen levels did not stay above 15 percent starting 200 million years ago, and there was no significant rise between 1000 and 700 million years ago.

Answer:

Oxygen levels remain below 5 percent starting 1000 million years ago.