What Are Extremophiles?

Extremophiles are organisms that have been discovered on earth that survive in environments that were once thought not to be able to sustain life. These extreme environments include intense heat, highly acidic environments, extreme pressure and extreme cold. Different organisms have developed varying ways of adapting to these environments, but most scientists agree that it is unlikely that life on Earth originated under such extremes.

Adapting to Extreme Heat

One type of extremophiles is called thermophiles. These organisms can survive at very high temperatures. In the 1960s, heat resistant bacteria were discovered in hot springs in Yellowstone National Park. This bacteria, thermus aquaticus thrives at temperatures of 70°C (160°F) but can survive temperatures of 50°C to 80°C (120°F to 175°F). A few years after these were discovered, other bacteria were found living under even more extreme conditions. Hydrothermal vents were discovered deep in the ocean and under such high pressure that the water boils at 340°C. It was a surprise to researchers to discover bacteria living and thriving in the vents at such extreme temperatures and pressures. Not only were there bacteria, but centimeters away where the water was cooler, was a complete ecosystem living off the bacteria. There were clams and tubeworms among other species. All of these organisms are sustained not from photosynthesis, but from the energy and carbon dioxide from the vents.

Some scientists believe that these vents may have been the origin of the first life on Earth. Others argue that because the chemistry these organisms use is based on (SO42-), it could not have developed until photosynthesis had developed elsewhere on Earth, because it was the development of photosynthesis that gave the ocean its current oxygen saturation.

Adapting to Extreme Cold

Other extremophiles have developed ways to cope with cold. Deep ocean water is as a fairly constant temperature of 2°C, but because of its salt content, in colder areas, ocean water can reach temperatures as low at -12°C without freezing. Extremophiles known as psychrophiles are known to survive at these low temperatures. Different species have come up with different ways to survive these cold temperatures. Some have developed substances, such as glycerol or antifreeze proteins which lower the freezing point of water by several degrees.

The main danger to organisms of freezing is the damage caused by ice crystals as water freezes and expands. Some species of  frogs and turtles have proteins which actually facilitate the freezing of body liquids. If the animal’s body liquids begin to freeze, a chain reaction is started and all of the body’s liquids freeze rapidly. This prevents the formation of ice crystals large enough to do any damage. Many kinds of microorganisms can survive freezing and thawing, as long as the problem of ice crystals is avoided. This can be accomplished in a laboratory by flash freezing - freezing the organisms very quickly in liquid nitrogen.

Some organisms have adapted to cold environments by forming symbiotic relationships with other organisms. Lichens are composite organisms that form when fungi form symbiotic partnerships with a photosynthetic partner - either an algae or a cyanobacteria. These lichens live on many rock surfaces in Antarctica, one of the driest, coldest environments on Earth and this partnership allows each species to survive and thrive in these environments.

Adapting to Extreme Pressure

There are many organisms on the ocean floor, even at great depths. Life has been found 11 km deep in the Mariana Trench. At this depth, organisms are under a pressure of 1,100 atmospheres. These organisms are difficult to study because creating such a high pressure environment in a laboratory is extremely challenging.

Isolated Ecosystems

There are still ecosystems on Earth that have not yet been explored. Some very interesting ones are high pressure underground lakes under the ice cap in Antarctica. These lakes are kept warm by geothermal energy and insulated by kilometers of ice above. These lakes have been separate from the rest of the Earth’s biosphere for millions of years, if not much longer or perhaps their whole existence. Scientists have drilled into one of the lakes, Lake Vostok, and plan to send a robot to collect water samples. This environment may be similar to some of the moons of Jupiter so exploring this environment and others like it are of particular interest to astrobiologists.


Tardigrades are impressive organisms. Also known as water bears because of their appearance, they have two strategies for survival in extreme environments. In case of flooding, these microscopic animals can inflate themselves into a balloon-like form and float to the surface of the water to get oxygen. They have another strategy which makes them one of the heartiest organisms known. In the case of drought or cold, these little animals can replace most of the water in their bodies with a sugar called trehalose. These sugar solutions do not form damaging ice crystals when frozen, and tardigrades have survived for over a century in museum samples, and many tardigrades survived a 12 day journey into the cold vacuum of space onboard the FOTON M3. Tardigrades protected by a UV filter almost all survived. Most of the ones without the filter did not.

Life Below Earth’s Surface

The astrophysicist Thomas Gold believed that the coal and oil underneath the Earth’s surface are not the long dead remains of plant matter and algae, but instead were incorporated into the Earth’s crust during accretion. He believed that these hydrocarbons provide the carbon for an underground ecosystem, perhaps completely isolated from our biosphere.

Several groups have now discovered microbes by digging many kilometers into the Earth’s crust and mantle. Some of these organisms were then tested to see if they could survive in those underground conditions, which would prove that they were not the result of contamination during the drilling process. Some of these microbes were put into a sealed flask with hot water, carbon dioxide and basalt for a year, and not only did they survive, they thrived under these conditions.

Whatever the source of the petroleum may be, (and most geologists still believe that it was formed by the remains of plant matter) there seem to be at least some forms of life living and thriving in it.


The variety of adaptations organisms make - to extreme temperatures and other extremes such as very acidic or very alkaline conditions - are very diverse. Biologically it is typically easier for organisms to adapt to chemical extremes than to physical extremes like temperature and high pressure.

One thing to keep in mind, is that even with life being found in such extreme location on Earth - under great pressure, at high temperatures, within solid rock - this is not evidence that life could form under these conditions. Many scientists believe that a more agreeable environment including liquid water, moderate pressure, and temperatures similar to those found on the surface of Earth would be needed for life to arise.