Résumé
An extreme environment is a habitat that is considered very hard to survive in due to its considerably extreme conditions such as temperature, accessibility to different energy sources or under high pressure. For an area to be considered an extreme environment, it must contain certain conditions and aspects that are considered very hard for other life forms to survive. Pressure conditions may be extremely high or low; high or low content of oxygen or carbon dioxide in the atmosphere; high levels of radiation, acidity, or alkalinity; absence of water; water containing a high concentration of salt; the presence of sulphur, petroleum, and other toxic substances. Examples of extreme environments include the geographical poles, very arid deserts, volcanoes, deep ocean trenches, upper atmosphere, outer space, and the environments of every planet in the Solar System except the Earth. Any organisms living in these conditions are often very well adapted to their living circumstances, which is usually a result of long-term evolution. Physiologists have long known that organisms living in extreme environments are especially likely to exhibit clear examples of evolutionary adaptation because of the presumably intense past natural selection they have experienced. The distribution of extreme environments on Earth has varied through geological time. Humans generally do not inhabit extreme environments. There are organisms referred to as extremophiles that do live in such conditions and are so well-adapted that they readily grow and multiply. Extreme environments are usually hard to survive in. Most of the moons and planets in the Solar System are also extreme environments. Astrobiologists have not yet found life in any environments beyond Earth, though experiments have shown that tardigrades can survive the harsh vacuum and intense radiation of outer space. The conceptual modification of conditions in locations beyond Earth, to make them more habitable by humans and other terrestrial organisms, is known as terraforming.
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