Extremophiles
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Extremophiles

Extremophiles come in many forms. For example, there are those that exist in the polar deepfreezes, those that survive in extremely dry conditions, those that thrive in highly acidic or saline environments, those that withstand to great pressure, and those that endure high levels of radiation.

Three or four billion years ago, earth was different in almost every way than the planet we know today. Immense volcanic eruptions, meteoritic bombardments, devastating comets, a suffocating atmosphere… the young earth was not the most hospitable place. Not to mention ultraviolet radiation from the sun, which, without today’s protective ozone layer, literally sterilized the planet’s surface. Nevertheless, life developed on earth. It is thought that this slow process may have started in the ocean, but many hypotheses have been developed to explain the mechanisms by which life originally appeared. To test these hypotheses, researchers study organisms that live on the edge of the possible, in highly extreme conditions. Such organisms are called extremophiles.

They come in many forms. For example, there are those that exist in the polar deepfreezes, those that survive in extremely dry conditions, those that thrive in highly acidic or saline environments, those that withstand to great pressure, and those that endure high levels of radiation. These images show some of the extreme environments inhabited by extremophiles, and they include hot, acidic lakes with huge colonies of extremophile bacteria (Yellowstone and White Island).

In the Antarctic, near Mt. Erebus, microorganisms live near the magma lake of this southern volcano. Not far from there are the McMurdo and Wright dry valleys, which lack snow and ice cover and are exceptionally dry and cold. A number of sites are of great interest to science. One of these, located along the Taylor glacier, features an outflow of iron-oxide-rich water (called Blood Falls) coming from a lake below the glacier that has been isolated from the rest of Earth’s biosphere for the past 5 million years. At least 17 species of bacteria live in this water. Not far away is Don Juan Pond, a body of water so salty—18 times the salinity of the oceans (the Dead Sea is eight times the salinity of the oceans)—that it never freezes. It is likely the most saline place on the planet, yet bacteria live there. These are all examples of the great adaptability of simple organisms to the extreme conditions that can occur on earth and that are potentially analogous to conditions on other planets. Lake Vostok is another famous case. This sub-glacial lake, the largest of the some 150 similar lakes discovered to date, is covered by four kilometres of ice. Water samples from the lake will be taken by a Russian robot at the end of 2012. Who knows what new forms of extremophiles it will discover.

In the Atacama desert, the driest place on earth outside of Antarctica, scientists study how life adapts to the almost total absence of water. In the crater of the Licancabur Volcano is a small lake. At an altitude of 5,916 metres and inhabited by algae and bacteria, it is probably the highest aquatic ecosystem on the planet.

Finally, the hydrothermal vents located on the ocean floors are exceptional places for discovery and exploration. These “submarine geysers” covered by an average of four to five kilometres of water are small oases where strange and unique creatures gather. Among them, the giant tube worm (Riftia pachyptila) is perhaps the most well known and the strangest inhabitant of these deep ecosystems. Up to two metres long and with a diameter of four to five centimetres, they have red “plumes” that they extend outside of a protective tube to feed on nutrients emitted by the vents. Bacteria living on these worms convert these chemical compounds (in particular, hydrogen sulphide — H2S) into sugars that they use for food. This alliance is a form of symbiosis, and this type of feeding is called chemotrophy.

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