There are three main groups of Archaeabacteria: Crenarchaeota, Euryarchaeota and Korarchaeota. Crenarchaeota are extremely heat tolerant, and Euryarchaeota survive in oxygen-free or salty habitats. Korarchaeota are the least understood of the groups.
Most Archaeabacteria are extremophiles that thrive in habitats that are inhospitable to most other life. Crenarchaeota are thermophiles, many of which also withstand sulfur and high acidity. These organisms live in volcanic habitats and hot springs. The pH of their environment ranges from 5 to 1, and they withstand temperatures over 230 degrees Fahrenheit.
Euryarchaeota contains halophiles, organisms that thrive in environments like salt lakes. This group also includes methanogens that live in anaerobic conditions, such as wetlands and even the intestines of other animals. Methane gas is the product of methanogen metabolism.
Like Crenarchaeota, Korarchaeota live in high-temperature habitats, such as hot springs. These organisms are primitive, and they are some of the least common Archaeabacteria in nature.
Archaebacteria and Eubacteria, or true bacteria, share a common ancestor, and Archaeabacteria are similar to true bacteria, as well as eukaryotic life. Research suggests that eurkaryotes rise, evolutionarily, from Archaeabacteria. Further, it is hypothesized that eukaryotes and Crenarchaeota have more in common than the different groups of Archaeabacteria have with one another.