Cyanobacteria

Previously known as blue algae, these bacteria possess chlorophyll in the same way as plants (in fact plants are photosynthetic thanks to their chloroplasts, which are cyanobacteria which have been ‘domesticated’ over the course of evolution!). Its photosynthesis activity frees up oxygen. It is this release of oxygen which led, from over 2 billion years ago, the amount of this gas in the Earth’s atmosphere to go from less than 1% to the 21% levels we have today.