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OUR atmosphere could once have had a much higher proportion of oxygen – as much as 35 per cent – according to recent experiments. This contradicts the notion that wildfires would have obliterated plant life if oxygen levels had ever been far above today’s norm of 21 per cent, which was based on experiments igniting strips of dry paper. A group led by Richard Wildman, now at the California Institute of Technology, decided to mimic real forests more closely. They put pine needles in a chamber where the oxygen content and the amount of moisture could be controlled, and set…