Archaea

These organisms have long been grouped with bacteria in the prokaryotic group (cells not containing a nucleus). Archaea are between 0.1 and 15 microns in size and often live in extreme environments (anaerobic, high salt content, very hot conditions, or at great depths). Their name (given to them by Carl Woese in 1977) comes from the fact that they were first considered to be ancient forms of life. This has since been questioned. Since this group first evolved, all living organisms have been divided into three groups: archaea, bacteria, and eukaryotes.