The term exobiology means is the study of life beyond the Earth. But since there's no known life beyond the Earth people say its a subject with no subject matter. It refers to the search for life elsewhere, Mars, the satellites of Jupiter and in other solar systems. It is also used to describe studies of the origin of life on Earth, that is, the study of pre-biotic Earth and what chemical reactions might have taken place as the setting for life's origin. From An interview with exobiology pioneer, Dr. Stanley L. Miller, UCSD Extremophiles Life on Earth is remarkably adaptable.
Organisms are able to survive under conditions previously thought impossible.
Specific examples of extreme environments that harbor life are sea ice, sub-seafloor hydrothermal systems, and subterranean basalt. From University of Washington astrobiology research pages . This is a term you will be coming across frequently in your reading. However, biochemically and genetically, they are as different from bacteria as you are. Archaeans include inhabitants of some of the most extreme environments on the planet.