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Chart of relative sizes of extremophiles
Archaea Bacteria Eukaryota
Archaea extremophiles: Sulfolobous, Halobacteria, Methanococcus, Pyrolobus
Bacteria extremophiles: Deinococcus, Thermotoga, Psychrobacter, Chroococidiopsis
Eukaryota extremophiles: Artemia, Hypsibius, Halicephalobous, Dunaliella
Hydrothermal worm
Ice worm
Tardigrade
Cryptococcus neoformans

Did you ever think life was possible deep under the ice in Antarctica or in volcanic vent in the ocean? Some microorganisms can survive in very harsh circumstances that would kill other living creatures. Scientists call them extremophiles, which means "lovers of extremes". We can find them in unexpected places like hot springs, soil, rocks, ice and even deep in the ocean. Studying and understanding extreme forms of life on Earth will help us in our search for life on planets with harsh environments. Although the list of extremophiles keeps getting longer as new ones are discovered, we will describe some of the most interesting:

Thermophiles - hot lovers
Psychophiles - cold lovers
Barophiles- pressure lovers
Halophiles - salt lovers
Radioresistant - radiation fighters

Thermophiles and hyperthermophiles are microorganisms that live in very hot water. They normally reside in hot springs or hydrothermal vents on the ocean floor, where temperature can vary between 50C/122F and 110C/230 F. Sulfolobus shibatae, discovered in acidic hot springs is a very interesting microorganism that is both a thermophile and an acidophile (an organism that thrives in an acidic environment).
Psychophiles are the opposite of thermophiles. They love very cold places and can thrive in temperatures below the freezing point of water. They reside in cold soils, ocean water, permafrost and even polar ice. In order to survive at such low temperatures, they have developed special proteins that act like antifreeze and lower the freezing point of water.
Salty environments will kill many microorganisms because the salt outside the cell will cause the water inside the cell to exit leaving cells dried out and incapable of carrying out normal functions. Halophiles are able to maintain the proper water balance in their cells because of special proteins. They can be found anywhere there is salt. They live in cold, hot, wet, dry, alkaline and neutral environments.
High pressure environments, such as those found at the bottom of the ocean, can kill many organisms. Not so with barophiles, which have developed mechanisms to thrive in these settings. In fact, some types of barophiles, known as obligatory barophiles, are so highly specialized that they cannot survive outside of these environments.
Radioresistant organisms can survive at very high level of radiation. They have excellent restoring systems that help them quickly repair damage caused by high energy radiation like solar UV radiation. The existence of such ability opens the possibility for the migration of life from one planet to another.
thermophile icon

Most thermophiles belong to the group of organisms called archaea. These single-celled organisms are something between eukaryotes and prokaryotes. They are considered the most primitive microorganisms on the Earth. They first appeared on our planet when it was much hotter.

lithoautotroph icon

Lithoautotrophs are strange microorganisms that live in rocks and soil. The name comes from 'lithos' (rock) and 'trophs' (consumers), meaning the "eaters of rock." These organisms are able to breakdown minerals in rocks to get energy. They can also get carbon from the air like plants.

tardigrade silhouette icon

Extremophiles that belong to more than one category are called polyextremophiles. A hypothetical polyextremophile combining the qualities of halophiles and barophiles might feel comfortable in the subsurface ocean of the Jovian moon Europa.

hot springs

A spring is a source of water that flows to the surface from somewhere underground.
A hot spring is a spring which has a water source that has been geothermally heated.

hydrothermal vents

Similar to geysers or hot springs, these are fissures on the sea floor which emit geothermally heated water.

Sulfolobus Shibatae

S. Shibatae is a species of the genus Sulfolobus, thermoacidophiles (single-celled organisms that thrive in both acidic and extremely hot environments)that are found in volcanic hot springs.

Permafrost

Thick sections of permanently frozen soil.

Ultraviolet

A type of raditation that's invisible to the human eye, since its wavelenghts are shorter than those of visbile light.
Ultraviolet light can be found in sunlight, and is responsible for sunburns when exposed to it for too long.