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Seen from the air, the irregular grid of evaporation ponds at the south end of San Francisco Bay in California is a kaleidoscopic quilt of reds and purples. These ponds take their colors from the single-celled microorganisms that live there, strange beings that thrive in concentrated salt solutions. Such extreme conditions kill almost every form of life on the planet, but not the haloarchaea, members of an ancient kingdom that existed even before Earth had an oxygen atmosphere. Archaea often live under impossible circumstances—boiling temperatures, lethal radiation, near-complete desiccation—which has led scientists to dub them "extremophiles." These prokaryotes may even be capable of hitchhiking through space. DasSarma describes the fascinating biology of these microbes, explaining how they are redefining the history of life on the planet and pushing the boundaries of cell physiology.