The amount of oxygen in the atmosphere has fluctuated over the last 600 million years, reaching a peak of about 30% around 280 million years ago, significantly higher than today's 21%.
The amount of oxygen in the atmosphere has fluctuated over the last 600 million years. The amount of oxygen in the atmosphere was reaching a peak of about 30% around 280 million years ago. This was significantly higher than today's 21%.