Even excluding our nearly ubiquitous high oxygen terrestrial environment, there is a remarkable diversity of extreme habitats on Earth (Table 6.2; Figures 6.1-6.4). These range from the ice at the poles to the searing heat of hydrothermal vents. Paralana Spring, in the Flinders Ranges of Australia, bubbles radioactivity (Figure 6.4). As suggested above, many of these have multiple extreme environments simultaneously. Thus, while the source of Octopus Springs in Yellowstone National Park is at the boilina pH ~8.2, a pH similar to that of the ocean, Congress Springs also is boiling but with a pH of near 0. Laguna Colorada, a hypersaline lake in the Bolivian Altiplano, has a moderately alkaline pH of 8.4, but is hypersaline and, thus, populated by halophiles. At an altitude of 4364 m, and a location of 22 °15.836' S; 67 °48.970' W, the organisms are also subjected
to exceptionally high levels of UVB radiation in the austral summer (Rothschild, unpublished).
An extreme environment that is poorly studied is that of the air. An airborne organism must deal with the effects of desiccation, decreasing temperature, ultraviolet radiation, and a nutrient-poor environment. Of course, with increasing elevation, oxygen decreases as well. The great microbiologist Louis Pasteur did some of the early work on aerobiology, but current work is conducted primarily for military reasons, to investigate spread of air-borne pathogens, and to preserve monuments.
While many extreme environments occur naturally, there are new, human-made environments as well. In particular, nuclear reactors (high radiation) and acid mine drainage (high metals, low pH) can provide novel challenges.
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