Type I

Type I atmospheres had appropriate levels of oxygen, nitrogen, and hydrogen to be breathable by the majority of species in the galaxy. Some contaminants or other trace gases could have had long-term detrimental effects. Planets with these types of atmospheres almost always had some form of indigenous life. Plant life or some analog that frees oxygen was present on all planets with a Type I atmosphere—all oxygen in the atmosphere would have been bound to other elements within a matter of months without such life to free it up.