Earth Log 0007 The First Two Billion Years

The question seems narrow, but the answer turns out to be most of what matters. By the time the period covered in this entry ends, the air had been remade, the ozone layer had formed, the oceans had begun to clear of dissolved iron, an entirely new kind of cell had been invented, sexual reproduction was in operation, and the first organisms had begun to live in cooperative bodies of many cells working as one. None of the species a casual modern observer would recognise existed yet. There were no animals, no land plants, no macroscopic fungi. There were only microbes, in unimaginable numbers, in seawater and shallow lagoons and damp rock and the cracks of the early crust. And yet by the time microbes were finished with the planet, almost every condition required for the later world was in place.