Archaebacteria (domain Archaea) are primitive bacteria that often live in extreme environments. This domain includes the following: 1) Thermophiles (“heat lovers”), which live in very hot environments, including the hot sulfur springs of Yellowstone National Park, which reach temperatures ranging from 140–176°F (60–80°C). 2) Halophiles (“salt lovers”), which live in locations with high concentrations of salinity, such as the Great Salt Lake in Utah, which has salinity levels that range from 15–20 percent. Seawater normally has a level of salinity of 3 percent. 3) Methanogens, which obtain their energy by using hydrogen gas (H2) to reduce carbon dioxide (CO2) to methane gas (CH4).