Life in extreme conditions
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D. radiodurans, a so-called extremophile, here on Earth (Credit: Michael J. Daly, Uniformed Services University of the Health Services) |
The more scientists look on Earth, the more life they find. Earthly life has adapted to an extraordinary variety of conditions, even those that humans had traditionally considered inhospitable. These life- forms are always single-cell microorganisms and they often derive their energy from chemical reactions. They can exist in the most surprising of places. We have found them in rocks in Antarctica, in volcanic springs in Yellowstone National Park, and even in hot-water geysers on the ocean floor. The microbes that live in these and other extreme environments are collectively known as extremophiles. An important limit for biological activity on the Earth is the temperature of the water in which the creature lives. This can be below 0°C, if the water does not freeze solid, or up to about 115°C, if the water does not boil. Other extremophiles include acid-loving and salt-loving microbes, and those that can exist at pressures greater than 350 times atmospheric pressure at sea level.
Microbes that can only live in scalding water are known as hyperthermophiles. They make up a particularly important branch of the extremophiles, because they appear to be among the most ancient species that live on Earth. Some scientists believe that this means life itself began in high-temperature environments, perhaps in the hot-water geysers on the ocean floor, known as black smokers. Although the extremophiles derive their energy from a wide array of chemical processes, they all rely on water and contain DNA. Perhaps exotic alien life uses another liquid other than water, or another information-carrying molecule other than DNA. Only space missions can find out.