The conditions surrounding us that we regard as ‘normal’ are capable of sustaining a huge diversity of life, but once environmental variables start to deviate from this normal situation it becomes much more difficult to survive. There are actually a surprising number of locations on Earth where conditions are far from normal, and these are termed extreme environments. They range from the boiling waters of volcanic hot springs to the icy wilderness of the polar deserts, from the hyper-saline soils of rain-starved deserts to the corrosive acid of mineral leachates, from the clouds in our atmosphere to potentially lethal radioactive wastes. 

Until relatively recently many such extreme environments were regarded as incapable of sustaining life, but a growing body of research is demonstrating that highly specialized life forms are found in virtually every extreme niche investigated to date. These incredibly tough organisms are called extremophiles and most are microbes.   They possess an amazing array of physical and biochemical adaptations that allow them to thrive in extraordinarily hostile conditions.