Extreme environment
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.