An extremophile (from Latin extremus meaning "extreme" and Greek philiā (φιλία) meaning "love") is an organism that thrives in and even may require physically or geochemically extreme conditions that are detrimental to the majority of life on Earth. In contrast, organisms from moderate temperature or neutral pH environments may be termed mesophiles or neutrophiles.
In the 1980s and 1990s, biologists found that microbial life has an amazing flexibility for surviving in extreme environments - niches that are extraordinarily hot, or cold, or dry, or under immense pressures - that would be completely inhospitable to complex organisms. Some scientists even concluded that life may have begun on Earth in hydrothermal vents far under the ocean's surface.[1]
Most known extremophiles are microbes. The domain Archaea contains renowned examples, but extremophiles are present in numerous and diverse genetic lineages of both bacteria and archaeans. Furthermore, it is erroneous to use the term extremophile to encompass all archaeans, as some are mesophilic. Neither are all extremophiles unicellular; protostome animals found in similar environments include the Pompeii worm, the psychrophilic Grylloblattodea (insects), Antarctic krill (a crustacean), and the "water bear".
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There are many different classes of extremophiles, each corresponding to the way its environmental niche differs from mesophilic conditions. These classifications are not exclusive. Many extremophiles fall under multiple categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.
Astrobiology is the field concerned with forming theories, such as panspermia, about the distribution, nature, and future of life in the universe. In it, microbial ecologists, astronomers, planetary scientists, geochemists, philosophers, and explorers cooperate constructively to guide the search for life on other planets. Astrobiologists are particularly interested in studying extremophiles, as many organisms of this type are capable of surviving in environments similar to those known to exist on other planets. For example, Mars may have regions in its deep subsurface permafrost that could harbor endolith communities. The subsurface water ocean of Jupiter's moon Europa may harbor life, especially at hypothesized hydrothermal vents at the ocean floor.
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]] An extremophile is an organism that thrives in extreme conditions that are harmful to most life on Earth. In contrast, organisms from moderate temperature or neutral pH environments may be termed mesophiles or neutrophiles.
In the 1980s and 1990s, biologists found that microbial life has a capacity for surviving in extreme environments. These are niches that are extreme in some way. They may be extraordinarily hot, or cold, or dry, or under immense pressures, or very salty or acidic. Such conditions are inhospitable to complex organisms. Some scientists suggest that life may have begun on Earth in hydrothermal vents far below the ocean surface.[1] High temperature habitats such as hot oceans, hot springs and deep ocean thermal vents would have occurred widely in the early Archaean eon (from 3.9 billion years ago). Adaptation to these conditions may have been crucial to the development of early forms of life.[2]
Most known extremophiles are microbes. The domain Archaea contains well-known examples, but extremophiles occur in bacteria as well. It is a mistake to use the term extremophile for all archaeans, as some are mesophilic. Nor are all extremophiles unicellular; protostome animals found in similar environments.
Some extremophiles fall under several categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.
   | Eukaryotes in extreme environments - Extreme eukaryotes (web) |
| | Extremophiles 2002 - Extremophiles 2002. [J Bacteriol. 2003] - PubMed Result |
| | Extremophilic microbes: Diversity and perspectives - DRS at National Institute Of Oceanography: Extremophilic microbes: Diversity and perspectives |
| | Fidelity of DNA synthesis by the ''Thermococcus litoralis'' DNA polymerase--an extremely heat stable enzyme with proofreading activity - Fidelity of DNA synthesis by the Thermococcus litoralis DNA polymerase--an extremely heat stable enzyme with proofreading activity. |
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