Extremophiles are proof of the toughness and variability of life. They are organisms found in conditions of cold, heat, pressure, dryness or darkness that are unendurable to humans. They can be found in hydrothermal vents deep beneath the oceans, in hot springs, in the dry valleys of Antarctica and in our deepest mines. They live where we cannot.
Most extremophiles are microscopic bacteria or Archaea. Not all are. The Pompeii worm, for example, Alvinella Pompejana, is the most heat tolerant animal on earth. It is about as long as an average hand, and of a fuzzy gray color. It has scarlet gills that resemble tentacles on its head and below that a structure resembling a small ball of yarn, which it uses to snag and feed on passing bacteria. It has a fleecy appearance caused by a shaggy coat of bacteria that live on it, feeding on mucus that the worm secretes for them, and possibly helping to insulate it from the scalding conditions in which it lives. Pompeii worms live in colonies of paper-like tubes on the lip of the mineralized chimneys of hydrothermal vents that release scalding water at the bottom of the ocean. At their tail end, they thrive in temperatures that may reach 176 degrees F. Their tentacled heads are usually in a cooler environment of about 72 degrees F. (22 C.), and it is possible that the worm vents heat from its gills to cool itself.
The Pompeii worm is not the only denizen of hydrothermal vents. They support a whole community of extremophiles. The basis of life there is chemoautotrophic bacteria. These organisms perform chemosynthesis, using the sulfur compounds produced by the hot vent to create food the way plants use water and sunlight for photosynthesis. These bacteria grow in a thick mat, which provides a food base for other members of this community, such as the tube worms, crabs, shrimp and fish. Some of the tiny organisms of this community are aerobic, that is dependent on oxygen produced by distant photosynthesis, but many are anaerobic, and could in theory survive if there were no sun.
Hot springs also shelter hyperthermophiles. In fact, they were first discovered in the hot springs of Yellowstone National Park. Many of these organisms are also able to survive conditions of high acidity and high radiation. Most hyperthermophiles need oxygen to carry out their life processes, but at least one, Aquifex pyrophilus, can substitute nitrogen for oxygen and grow without it. Thermus aquaticus, which was discovered in a Yellowstone spring, produces polymerase, the key enzyme in polymerase chain reaction, which is used extensively in investigating DNA.
Another place to find extremophiles is Antarctica. The McMurdo Dry
Valleys are barren of ice and snow. The average annual temperature is 68 degrees below zero. They are whipped by gravity-fed karabatic winds which suck moisture from the exposed gravel. Here, endolithic plants and bacteria live within the rock, drawing sustenance from the trickle of summer melt water. Their lives are so attenuated that the single-celled organisms may divide once in a thousand years or more. Research here gives us an idea of what possible life forms could survive off our kind planet.
These are only a few of the extremophiles earth holds. There are organisms that thrive in extremely salty conditions, halophiles. Acidophiles and alkaliphiles grow in environments that are extremely acid or base. Drilling through volcanic deposits on the island
of Hawaii, geologists believe they have discovered organisms living within rock 4000 feet deep. Extremophiles indeed!