But on Parnassus greenhouse gases, on small "islands", a poisonous, from a general point of view, areas survived small, but very special bacteria . And they were special because, unlike all, they produced not carbon dioxide, but oxygen. They were called cyanobacteria. These babies, however, are not noticeable for themselves, they have launched a irrevocable and incomparable process. 2 000 million years they filled the earth with oxygen, which at first locally accumulated at the bottom of small bodies of water, where they lived, building their houses. Amazing creatures clearly realized the principle of " more haste, more waste.". Careful, but enterprising bacteria began from the ocean and for 600 million years "oxidized" it first. It would seem that you can stop, but where there! At the turn of 1.8 billion years ago, oxygen, produced by bacteria, has already oxidized all the near-surface rocks on the earth, and finally it will do it in a billion years. After that, saturating the atmosphere with oxygen does not seem so difficult. In just over 300 million years, the atmosphere has reached its present state. But the story does not end there. Babies bacteria and now build their cyanobacterial mats - carbonate building, similar to limestone. You can see them live (!) in Australia. In addition, industrious cyanobacteria even now produce 20 to 40% of the total oxygen content on earth, and in South America and China one makes from them flour.