Our results show that over a period of around 3 million years - which is very rapid in geological terms - the oxygen levels in the atmosphere jumped from around 15% to around 19%. For comparison, there is 21% oxygen in today’s atmosphere. We really don’t know what might have caused this increase, but we also see a drop in CO2 levels at that time.”
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Don’t know the cause? Ahhh...plants?
This is the kind of thing that gives me such faith in the AGW predictions.