Red-green algae and fine white 'beards' of bacterial mat cover the lava blocks 200 meters underwater, a rare overlap of the chemosynthetic and photosynthetic communities. © Universal History Archive/UIG via Getty Images
Asked by: John Corfield, Witheridge
For the first billion or so years of life on Earth, the only organisms were chemosynthetic bacteria, which grew as mats in shallow seas and by volcanic hydrothermal vents. The very first cells probably metabolised hydrogen sulphide and carbon monoxide. Eventually photosynthetic bacteria evolved and used sunlight to build sugars from carbon dioxide and water. Organisms that eat other organisms didn’t emerge until around 1.2 billion years ago – over two billion years after life first emerged.