Free-living, quickly-reproducing, sunlight-and-carbon-dioxide-eating bacteria rapidly become one of the most successful lifeforms on the planet.

They invade every niche where light ever reaches. In the early eons[1] of the planet, they are responsible for massive climate change: they multiply so effectively, they reduce the carbon dioxide in the atmosphere from a high level down to much lower levels. Incidentally, this causes the extinction of many oxygen-intolerant early forms of life.

They are first clearly present around 2.5 billion years ago, and survive to the present day in great quantities in many locations, from the blue-green algae which blooms on the Mediterranean to the camouflaging bacteria which turns sloths fur dark green.

Oh, but before we finish, there is one more place you may be currently evolving to live…