From Garry Marley, Stillwater, Oklahoma, US
I enjoyed Rowan Hooper’s revisitation of the great origins-of-life theories, in particular Freeman Dyson’s idea that biochemistry preceded cell biology on the primordial Earth. A key component of Lynn Margulis’s endosymbiosis model was the acquisition of photosynthetic bacteria by proto-cells, making it possible for plant cells to fix carbon into glucose (30 May, p 40).
Of course, in deep-sea hydrothermal vents, the lack of light makes photosynthesis impossible. So, the archaeal species there use chemosynthesis, by which electrons from dissolved hydrogen sulphide gas are used instead of water to turn carbon dioxide to glucose, gleaning a sulphur by-product instead of oxygen. Whenever migration to a light-rich surface was feasible, perhaps photosynthesis evolutionarily succeeded chemosynthesis, enriching our atmosphere with oxygen.
