Archaea (Archaebacteria) Temporal range: 3.5-0Ga Had'n Archean Proterozoic Pha. Paleoarchean or perhaps Eoarchean – recent
Halobacterium sp. strain NRC-1, each cell about 5 μm long
Scientific classification
Unrecognized taxon (fix):	Archaea
Kingdoms and phyla
"Euryarchaeota" Woese et al. 1990 "Methanopyri" Garrity and Holt 2002 "Methanococci" Boone 2002 "Eurythermea" Cavalier-Smith 2002 "Neobacteria" Cavalier-Smith 2002 "DPANN" "ARMAN" "Micrarchaeota" Baker et al. 2010 "Parvarchaeota" Rinke et al. 2013 "Aenigmarchaeota" Rinke et al. 2013 "Diapherotrites" Rinke et al. 2013 "Nanoarchaeota" Huber et al. 2002 "Nanohaloarchaeota" Rinke et al. 2013 "Pacearchaeota" Castelle et al. 2015 "Woesearchaeota" Castelle et al. 2015 "Proteoarchaeota" Petitjean et al. 2015 (TACK)"Filarchaeota" Cavalier-Smith, T. 2014 "Aigarchaeota" Nunoura et al. 2011 "Bathyarchaeota" Meng et al. 2014 Crenarchaeota Garrity & Holt 2002 "Geoarchaeota" Kozubal et al. 2013 "Korarchaeota" Barns et al. 1996 Thaumarchaeota Brochier-Armanet et al. 2008 "Asgardarchaeota" Violette Da Cunha et al., 2017 "Lokiarchaeota" Spang et al. 2015 "Thorarchaeota" Seitz et al. 2016 "Odinarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017 "Heimdallarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017
Synonyms
Archaebacteria Woese & Fox, 1977 Mendosicutes Gibbons & Murray, 1978 Metabacteria Hori and Osawa 1979

Colourful archaea at Midway geyser

The Archaea (or Archea) are a group of single-celled organisms. The name comes from Greek αρχαία, "old ones". They are a major division of living organisms.

Archaea are tiny, simple organisms. They were originally discovered in extreme environments (extremophiles), but are now thought to be common to more average conditions. Many can survive at very high (over 80 °C) or very low temperatures, or highly salty, acidic or alkaline water. Some have been found in geysers, black smokers, oil wells, and hot vents in the deep ocean. Recent research has found ammonia-eating archaea in soil and seawater.

In the past they had been classed with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this is a mistake. The Archaea have an independent evolutionary history and show many differences in their biochemistry from other forms of life. They are now classified as a separate domain in the three-domain system. In this system, the three distinct branches of evolutionary descent are the Archaea, Bacteria and Eukaryota.