Archaea comes from the Greek word meaning “ancient.” An appropriate name, because many archaea thrive in conditions mimicking those found more than 3.5 billion years ago. Back then, the earth was still covered by oceans that regularly reached the boiling point — an extreme condition not unlike the hydrothermal vents and sulfuric waters where archaea are found today.
Some scientists consider archaea living fossils that may provide hints about what the earliest life forms on Earth were like, and how life evolved on our planet.
Archaea can be found in many"extreme environments": highly sulfurous lakes (right); ); ice (top left); Utah‘s Great Salt Lake (above middle); and hot geysers like the Lonestar (above middle); and in undersea hydrothermal vents (above right).
In addition to superheated waters, archaea have been found in acid-laden streams around old mines, in frigid Antarctic ice and in the super-salty waters of the Dead Sea. A number of other extreme-living bacterial species also enjoy these conditions, too, such as the community of cyanobacteria and bacteria shown above.
Thermophiles like unusually hot temperatures. A few species have been found to survive even above 110 degrees Celsius (water boils at 100 degrees Celsius).
Psychrophiles like extremely cold temperatures (even down to -10 degrees Celsius).
Archaea that populate extreme environments (along with some of their bacterial cousins) have developed some clever tricks and tools to do so. For example, they produce special enzymes that help keep all the parts of their cells intact even in conditions that would have our human skin falling apart.
Many archaeans thrive in conditions that would kill other creatures: boiling water, super-salty pools, sulfur-spewing volcanic vents, acidic water and deep in Antarctic ice. These types of archaea are often labeled "extremophiles," meaning creatures that love extreme conditions.
Archaeans have been found that can live in temperatures above 212°F (100°C). In contrast, no known eukaryotes can survive over 140°F (60°C). Other archaeans have been found in an Antarctic lake with a surface that is permanently frozen.
How do these extremophiles do it? They make a variety of protective molecules and enzymes (en-zimes). For example, some archaeans live in highly acidic environments. If the acid got into the archaeal cells, it would destroy their DNA, so they have to keep it out. But the defensive molecules on their cellular surfaces do come into contact with the acid and are uniquely designed not to break apart in it. Archaeans that live in very salty water are able to keep all the fluid from dissolving out of their cells by producing or pulling in from the outside solutes such as potassium chloride that balance the inside of the cells with the salty water outside. Other enzymes allow other achaeans to tolerate extreme hot or cold.
Not all the archaea are extremophiles. Many live in more ordinary temperatures and conditions. For example, scientists can find archaeans alongside bacteria and algae floating about in the open ocean. Some archaeans even live in your guts.