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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.