Archaebacteria are a group of most primitive prokaryotes which are believed to have evolved immediately after the evolution of the first life. They are of three types: methanogens, thermoacidophiles and halophiles.
Methanogens live in oxygen-free environments (anaerobic conditions) and produce methane gas. They are named for their unique method of harvesting energy by converting H2 and CO2 into methane gas. Because oxygen is a poison to them, methanogens can live only in anaerobic conditions, such as the bottom of swamps and in sewage. The methane produced by methanogens living in the waters of swamps, sewage, or marshes is called swamp gas.
Methane produced in the digestive tracts of many animals including humans is called intestinal gas. In the digestive track of cows they break down cellulose, enabling cows to use nutrients in grass and plants. They are used in industry to treat sewage and to help purify water.Example of Methanogens: Methanococcus, Methanobacterium
Thermoacidophiles can live in water that is extremely hot (230 degrees F.) And acidic (pH less than 2), two conditions that would kill other organisms. Can be found around hot springs like those at Yellowstone national park, no other organism can live in these waters.
Thermoacidophiles live near volcanic vents on land or near hydrothermal vents, cracks in the ocean floor miles below the surface that leak scalding acidic water.Example of Thermoacidophiles: Thermoplasma and Thermococcus
Halophiles live in extremely salty conditions. Found in the great salt lake in Utah and the Dead sea. Can grow in water that is up to ten times saltier than seawater. High salt concentrations would kill most bacteria, but this high concentration is beneficial to the growth of extreme halophiles, and these organisms use salt to generate ATP.