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Quote:
| Originally Posted by [b Quote[/b] (Steve W @ Feb. 26 2004,14:25)] Quote: | Originally Posted by [b Quote[/b] (Kate R @ Feb. 26 2004,13:56)]right, now when did plants start photosynthesising..... | good one Kate 
about three billion years ago for the appearance of the first photosynthesizing marine algae and about two billion years ago there's the first evidence of O2 in the atmosphere |
well if we're
really going to get technical, we'd have to ask when did the %O2 get to 20.9, and therefore become 'air' as we currently define it........