"Extremophiles" are microorganisms with the ability to thrive in extreme environments such as hydrothermal vents.
Since they live in “extreme environments” (under high pressure and temperature), they can tell us under which range of conditions life is possible.
The unique enzymes used by these organisms, called "extremozymes," enable these organisms to function in such forbidding environments. These creatures hold great promise for genetically based medications and industrial chemicals and processes.
It's important to note that these organisms are 'extreme' only from a human perspective. While oxygen, for example, is a necessity for life as we know it, some organisms flourish in environments with no oxygen at all.