Life in extreme environments

Each recent report of liquid water existing elsewhere in the Solar System h as reverberated through the international press and excited the imagination of humankind. Why? Because in the past few decades we have come to realize that where there is liquid water on Earth, virtually no matter what the ph ysical conditions, there is life. What we previously thought of as insurmou ntable physical and chemical barriers to life, we now see as yet another ni che harbouring 'extremophiles'. This realization, coupled with new data on the survival of microbes in the space environment and modelling of the pote ntial for transfer of life between celestial bodies, suggests that life cou ld be more common than previously thought. Here we examine critically what it means to be an extremophile, and the implications of this for evolution, biotechnology and especially the search for life in the Universe.