Archaeal Means and Extremes

The discovery of single-celled bacteria that live in the extreme temperatures of hydrothermal vents deep in the ocean or in hot springs on land led to the discovery of a third branch of life--the Archaea. In his commentary, DeLong summarizes new evidence showing that Archaea are not confined to extreme living conditions but can be found in abundance as planktonic organisms in cold ocean waters below 100 m. Their occupation of this enormous habitat qualifies these organisms as one of the most abundant prokaryotes on Earth.