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Archaeans are prokaryotes in the Archaea Domain. They were first discovered in extreme environments such as hot springs. For a long time, they were classified as bacteria. As more was learned about them, however, they were found to be quite different from bacteria. They were finally placed in their own domain in the late 1970s. Scientists still know relatively little about archaeans, and new species of archaeans are being discovered all the time. Many, but not all, archaeans are extremophiles. Extremophiles are organisms that live in extreme conditions. For example, some archaeans live around hydrothermal vents. Boiling hot, highly acidic water pours out of the vents. These extreme conditions don't deter archaeans. They have evolved adaptations for coping with them. Such conditions are also like those on ancient Earth. This suggests that archaeans may have evolved very early in Earth's history.
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