Archaea

The ability of many members of the Archaea to thrive in environmental conditions that we would find extreme is perhaps one of their most fascinating characteristics. There are genus like Halobacterium, which inhabit extremely salty environments, such as the Great Salt Lake in Utah and the Dead Sea in Israel. The salt concentration in these lakes is at least ten times that of seawater. Still other lakes, like Lake Magadi in Kenya, are not only extremely salty, but are also extremely alkaline, with pH values as high as 10 or 12. Archaea can be found even here, and their names reflect their habitat: Natronobacterium, Natronosomonas, and Natronococcus ("natro" means "salt"). The reddish-purple color sometimes seen in seawater-evaporating ponds, where solar salt is prepared, is the result of the growth of red-pigmented Archaea.

Extremes of temperature offer no challenge to certain members of the Archaea. A number of species, in fact, require temperatures over 80 °C in order to grow. Some live quite happily in the superheated outflow of geothermal power plants. Others thrive in the conditions of extreme acidity and temperature found in sulfur-rich, acidic hot springs like those in Yellowstone National Park, in the United States.

Archaea bacteria are also known as "extremophiles," thanks to their ability to survive in extreme environments such as very hot and very cold climates.

Archaea also populate the areas surrounding deep-sea vents, underwater volcanoes that form when the earth's crust opens along the ocean floor's spreading centers. The deep-sea vents have the hottest temperatures at which any living organism has been found. As of 2001, the current record for heat tolerance belonged to Pyrolobus fumarii, which can grow in water at a maximum temperature of 113 °C, well above boiling. At the opposite extreme, Archaea are among the few organisms found in the frigid waters of the Antarctic.