The lost civilization of Atlantis may just be legend, but way down below the ocean (to quote the folksinger Donovan) there are some things that are very real — namely, bacteria and archaea. By some estimates, sub-seafloor prokaryotes may account for two-thirds of the biomass of these types of organisms on Earth. The latest evidence for such a huge undersea biosphere, and a depth record of sorts, is reported in Science by R. John Parkes of Cardiff University and colleagues. They have found living prokaryotes 5,335 feet below the ocean floor off Newfoundland, about twice as deep as the previous...