Archaea

One of the three domains of life: single-celled prokaryotes that superficially resemble bacteria but are biochemically distinct, with cell membranes and RNA-processing machinery closer to eukaryotes in some respects. First recognized as a separate domain from genetic sequencing in the late twentieth century, archaea are especially associated with extreme environments (hot springs, salt lakes, deep-sea vents) though they are now known to be common in ordinary soil and ocean water too.