Carbon dioxide levels now are much lower than they were when cells first arose. Oxygen levels are much higher.
Work Step by Step
The first cells arose 3.8 billion years ago. On the graph, it shows the carbon dioxide line much higher on the y-axis than modern day carbon because the line steadily decreases. Oxygen levels have been increasing since 3.8 billion years ago because the line was much lower on the y-axis 3.8 billion years ago than it is now.