Future research can identify what geological processes are consistent with these findings "and thus help to identify the major processes that control atmospheric oxygen levels," Stolper said.
These findings also reveal what might be a strange contradiction, because it could be assumed that atmospheric carbon dioxide levels should rise as oxygen levels fall — "for example, right now we are consuming oxygen and breathing out carbon dioxide," said study senior author John Higgins, a geochemistat Princeton.
However, previous research has found that atmospheric carbon dioxide levels have not, on average, changed over the past 800,000 years, Higgins noted. "At first glance, these two sets of observations, both from gases trapped in ice cores, are paradoxical," he said. One way out of this conundrum is a well-known but relatively untested concept that suggests "that on timescales longer than a few hundred thousand years, atmospheric carbon dioxide and Earth's temperature are regulated via a 'silicate weathering thermostat,'" Higgins said.