Claim: Extreme environments can be caused by Toxicity.

An extreme environment contains conditions that are hard to survive for most known life forms . These conditions may be extremely high or low temperature or pressure ; 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 or sugar ; presence of sulphur , petroleum , and other toxic substances .   Examples of extreme environments include the geographical poles , very dry deserts , volcanoes , deep ocean trenches , upper atmosphere , Mt Everest , 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 .