Carl Woese, who discovered a third domain of life —the archaea — has died, reports The New York Times. He was 84. In 1977, Woese, who worked at the University of Illinois at Urbana-Champaign, and his colleagues uncovered a group of single-cell organisms that were different from the known groups of prokaryotes and eukaryotes. By examining and comparing the ribosomal DNA of archaea, Woese was able to determine that archaea had evolved separately from a common ancestor shared by prokaryotes and eukaryotes, the Times notes. "He put on the table a metric for determining evolutionary relatedness," Norman Pace, a microbiologist and biochemist at the University of Colorado, Boulder, tells the Times. "His results were the first to prove that all life on earth was related."