What happened during the "Great Oxidation Event"?
AOxygen increased in the atmosphere, causing a mass extinction
BOxygen decreased in the atmosphere, preventing a mass extinction
COxygen increased in the atmosphere, preventing a mass extinction
DOxygen decreased in the atmosphere, causing a mass extinction
AOxygen increased in the atmosphere, causing a mass extinction
BOxygen decreased in the atmosphere, preventing a mass extinction
COxygen increased in the atmosphere, preventing a mass extinction
DOxygen decreased in the atmosphere, causing a mass extinction