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Temporal range: Archaean – Recent
|Halobacteria sp. strain NRC-1, each cell about 5 μm long.|
Woese, Kandler & Wheelis, 1990
|Kingdoms and phyla|
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 classification 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.
- No archaean species can do photosynthesis.
- Archaea only reproduce asexually.
- Archaea show high levels of horizontal gene transfer between lineages.
- Many archaea live in extreme environments.
- Unlike bacteria, no archaea produce spores.
- Archaea are common in the ocean, and especially in the plankton. They make up to 20% of all microbial cells in the ocean.p475
- Carl Woese discovered the Archaea by 1978, and proved it was a separate Kingdom by 1990.
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