Archaean Era only have single cell organism, at first(about 3800 million years ago) they can only "eat" sulphur compounds as food; After 800 million years some of them could use sunlight to produce food(this type of bacteria[cyanobacteria] can only be find in south Africa coast, and some scientists believe that they some how infected the ancestor of modern plant without harm to it, and some how they do not get out, and become the chloroplast of plant cell), and some can store nitrogen caompounds(this type of bacteria can find in soil today). From the color of sky, we can know that the atmospheric conponent is very different from now, poisonous gas are common components.