The Archaea have no nuclear membrane and have distinct biochemistry and RNA markers from bacteria. The Archaeans are considered some of the oldest species of organisms on Earth. They feed on inorganic matter. The only easy way to distinguish them on sight from “true” bacteria is by the extreme, harsh environments in which they notoriously thrive. The domain Archaea makes up one of the domains of life in the three-domain system; the two other domains are Bacteria (which like bacteria, is also prokaryotes) and Eukarya.