Life at High Temperatures
by Thomas D. Brock
Beneath the ground in Yellowstone is an enormous body of molten rock, the remains of earlier volcanic activity. Water from rain and snow percolates into the ground and becomes heated to very high temperatures. Under great pressure, this hot water rises to the surface through cracks and crevices. As it rises, it dissolves chemicals from the surrounding rocks. The water of Yellowstone's thermal features is thus not only hot, but mineralized. One important mineral, silica, deposits as it cools, forming the cones and rims of the thermal features. Other minerals provide the nutrients that feed the microorganisms. Still other minerals, such as arsenic and mercury, are toxic, although the organisms of the hot springs have learned to tolerate them. Also present are gases, of which hydrogen sulfide is the most important (smell of rotten eggs). Acid springs are formed when hydrogen sulfide meets oxygen of the air and is changed into sulfur and sulfuric acid by bacteria called sulfur bacteria.
Diagram showing the origins of a thermal system
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