Evolution of Prokaryota and Eukaryota:
Bacteria, Archaea, and Eukaryota

Though superficially similar, molecular evidence indicates an extremely ancient separation between Bacteria and Archaea. Modern Archaea are found in extreme environments requiring methanogenic, halophilic, or thermophilic metabolisms. Though they lack a nuclear membrane and are therefore described as prokaryotic, Archaea share with Eukaryotes several aspects of their genetic system, including an intron / exon gene structure.