Bacteria
From Palaeos.org
"Bacteria" is the term used to designate all non-photosynhetic prokaryote microorganisms. These are simple rod-, sphere, and curvy spiral- shaped organisms, usually only a few microns long, or less, that constitute not only the simplest but also the most abundant and prolific life on Earth.
It has since been discovered that there two very different types of bacteria; the standard bacteria or "Eubacteria", and anaerobic bacteria or "Archaea" (originally called "Archeobacteria", and not to be confused with the Archean eon, although that may be when they first appeared), which are metabolically and structurally very different. Also included among the bacteria would be the hypothetical Last (most recent) Universal Common Ancestor, "LUCA" for short, the postulated ancestor of all living organisms on Earth, which lived somne time during the early Archean or perhaps even the late Hadean era.
