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A steaming pool of water might not seem particularly hospitable to life, but some organisms thrive in such environments. Extremophile microbes live in many hot springs, like Grand Prismatic spring in Yellowstone National Park, U.S.A. (shown here). Different strains of thermophiles give this pool its range of hues; extreme heat-lovers dwell in the hottest central portions of the pool, while the cooler edges are inhabited by other, different-colored species.
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Image courtesy of the U.S. Natl. Park Service, photograph by Al Mebane.


Some environments are inhospitable to most "normal" living creatures. However, these extreme environments are not necessarily lifeless. Certain types of organisms, known collectively as "extremophiles", have adapted to survive or even thrive in various types of extreme environments. Philia is the Greek word for "love", so extremophiles are organisms that "love" extreme environments.

Most, though not all, extremophiles are microbes. In the last few decades, scientists have discovered many types of organisms that can survive in difficult environments that were previously thought sterile. Extremophiles have been found in very hot and in very cold environments; in exceptionally dry deserts; in environments that are very acidic or alkaline or doused in other harsh chemicals; and even in places exposed to high levels of radiation. These discoveries have generated lots of interest in life in extreme environments in recent years.

Early in our planet's history, most environments on Earth were extreme by modern standards. Likewise, environments on alien worlds within our Solar System and beyond are often marginally habitable if at all. The study of extremophiles may shed light on the origins and early evolution of life on Earth. Likewise, our knowledge of extremophiles may help us gage the likelihood of life arising in various extreme environments on planets and moons in our Solar System and beyond. The relatively new science of astrobiology is concerned with the study of such organisms.

Scientists have special names for extremophiles that thrive in specific types of challenging environments. Thermophiles live in hot environments (60-80 C, or 140-176 F); hyperthermophiles live in really hot places (80-122 C, or 176-252 F). Acidophiles like acidic conditions, with a pH of 3 or lower. Halophiles live in salty environments, cryophiles (or psychrophiles) like the cold, and xerophiles thrive in very dry deserts. Some organisms live in environments that are extreme in multiple ways; certain microbes that dwell in acidic hot springs are thus both thermophiles and acidophiles.

Though not technically extremophiles, numerous larger organisms are also adapted to survive in environments that would be lethal to most creatures. Camels are famously capable of going for long periods without water in the deserts in which they live. Emperor penguins somehow manage to make it through bitter Antarctic winters. Extreme plants, such as the many species of cactus, cope with the heat and dryness of desert environments as well. Bizarre tube worms grow in the superheated and chemically exotic niches around deep sea hydrothermal vents.

Last modified September 26, 2008 by Randy Russell.

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Traveling Nitrogen is a fun group game appropriate for the classroom. Players follow nitrogen atoms through living and nonliving parts of the nitrogen cycle. For grades 5-9.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA