The Domain Archaea wasn't recognized as a major domain of life until quite recently, largely through the work of Dr. Carl Woese and his colleagues at the University of Illinois. Archaeans don't look that different from most bacteria under the microscope; since most of them are extremely difficult to culture, their unique place among living organisms long went unrecognized. However, biochemically and genetically, they are as different from bacteria as you are. Although many books and articles refer to them as "Archaebacteria," they aren't bacteria - they're archaea.
Archaeans include inhabitants of some of the most extreme environments on the planet. Some live near rift vents in the deep sea at temperatures well over 100 degrees Centigrade. Others live in hot springs, in extremely alkaline or acid waters, or in extremely saline water: these pictures show an immense bloom of archaeans in a saline pond at a salt works near San Quintin, Baja California, Mexico. This archaean, Halobacterium, also lives in enormous numbers in salt ponds at the south end of San Francisco Bay; interested residents of this area should take the Dunbarton Bridge for the best views. Archaeans may be the only organisms that can live in such extreme conditions, and may be extremely abundant in hostile environments. New research is showing that archaeans are also quite abundant in the plankton of the open sea.
For information on the phylogeny of archaeans, we recommend the archaebacterian pages of the Tree of Life exhibit at the University of Arizona.
