The Earth had essentially no oxygen until 2.4 million years ago, yet life started at 3.4-3.6 byo:-http://www.newscientist.com/article/mg22329792.700-oxygen-oasis-for-early-life-found-in-ancient-rock.html#.U9BChNIg_Vg-We need oxygen. Having anaerobic bacteria first to make oxygen sounds lilke preplanning rather than chance.