The third domain of life

By Oliver Morton

In a graphic novel by the great Alan Moore, "The Ballad of Halo Jones", Halo shares a cabin on a starship with two companions, Toy and the Glyph. But Halo and Toy think they are just a twosome. The Glyph has so little personality that no one, even in cramped quarters, notices her—or possibly him—without the closest attention. Even then, any memory of the Glyph soon fades.

As on the starship Clara Pandy, so on Earth. Life seems to come in two forms: things with big complicated cells, and things with small simple cells. Amoebae, aardvarks, aspergilli, aspidistras and apes like us fall into the first category, known as eukaryotes. Bacteria fall into the second. Pay attention, though, and a third category appears: the archaea.