ice core analyses indicates atmospheric oxygen levels have fallen 0.7 percent over the past 800,000 years /

(Phys.org)—A small team of researchers with Princeton University has found evidence that suggests that the amount of oxygen in the soil's atmosphere has dropped by 0.7 percent over the past 800000 years. In their paper published in the journal Science, the team describes their analyses of ice core samples taken from Antarctica and Greenland and offer some possible explanations for what they found.

Source: phys.org