The three types of archaebacteria each use a different type of method to create ATP, which include converting methane in ATP by the methanogens, the use of aerobic respiration or conversion of light energy by the halophiles and theromophiles converting hydrogen sulfide to create ATP. These types of bacteria are kept in a class by themselves because of the conditions they often populate. The archaebacteria are the oldest known living organisms in the world.
Methanogens are unique in the fact that they cannot exist in oxygenated environments. These bacteria are mostly found in areas like bogs, sewage and even intestines. Common bacteria cannot survive in areas with high salt content, but in the archaebacteria classification there is an exception to that. Halophiles thrive in high salt environments like the Dead Sea or the Great Salt Lakes. Halophiles unlike the other types of archae can switch what type of energy creating process they use from aerobic respiration to photosynthesis with a pigment called bacteriorhodopsin. Thermophiles live in areas of high acidity and heat. They can survive temperatures up to 230 degrees Fahrenheit, which makes volcanic vents and hydrothermal vents ideal areas for them to thrive. Their forms can withstand pH as low as 2. These types of bacteria, despite their uniqueness are classified as prokryates.