Going to extremes

Life can exist in the strangest inhospitable places on earth. It are mostly bacteria or algae that apperently choose extreme lifeconditions.Especially in the deep-seas live so-called "super-thermophilic" (=extremely-heatloving) micro-organisms, these not only exist, but thrive at temperatures even beyond 150 ° C (Baross & Deming, 1993). They inhabit pressurized enviroments beneath deep-sea hydrothermal vents. At this temperatures you might expect the water to boil, but it doesn't because of the immense pressure. Recently bacteria were discovered which live at an astonishing 169 ° C! It's not only the temperature, lots of organisms at places where no sunlight ever comes use chemicals like hydrogen sulfite as their energy source. The bacteria inturn sustain larger organisms in the ventcommunity. Also well into the Earths crust, the toplayer of the earth, microbes are found. The mounting pressure has little direct effect on them even at several kilometres below groundlevel. It is the increasing temperature that limits the depth of life beneath the surface. In the oceanic crust the temperature rises about 15 ° C per kilometre. So microbial life extends on average about 7 kilometres below the sea floor. For continental crust the microscopic life should reach almost 4 kilometres into the earth, for the surface temperature is approximately 20 ° C and it rises with 25 ° C per kilometre. However the amount of micro-organisms will vary from place to place.
BacteriaFrom biology-courses we know that bacteria have an optimum curve, which means that at certain temperatures they have a peak where they thrive most. At too cold temperatures they go into somesort of stasis, you could compare it with hibernation, and they do not show any characteristics of life. If the temperatures increase they become active again. At too hot temperatures, however, they are damaged too severly that the damage is irretrivable.