Every morning at Hamelin Pool, in Western Australia, the first rays of sunshine illuminate knobby reef-like structures, submerged or peeking just above the gentle waves, depending on the tide. On the crudely rounded surfaces of these rocks, microorganisms stir and begin the daily task of photosynthesizing, fighting against occluding sand grains to harvest the sunlight.

This scene, or something like it, has likely been occurring every morning, somewhere on Earth, for the last 3.7 billion y