obvious morphological similarities, divided life into 23 main divisions, incorporated within three domains: Bacteria, Archaea, and Eucarya. Acceptance of the validity of Woese's phylogenetically valid classification was a slow process. Prominent biologists including Salvador Luria and Ernst Mayr objected to his division of the prokaryotes. Not all criticism of him was restricted to the scientific level. A decade of labor-intensive oligonucleotide cataloging left him with a reputation as "a crank," and Woese would go on to be dubbed as "Microbiology's Scarred Revolutionary" by a news article printed in the journal Science. The growing body of supporting data led the scientific community to accept the Archaea by the mid-1980s. Today, few scientists cling to the idea of a unified Prokarya. Woese's work on Archaea is also significant in its implications for the search for life on other planets. Before the discovery by Woese and Fox, scientists thought that Archaea were extreme organisms that evolved from the microorganisms more familiar to us. Now, most believe they are ancient, and may have robust evolutionary connections to the first organisms on Earth. Organisms similar to those archaea that exist in extreme environments may have developed on other planets, some of which harbor conditions conducive to extremophile life. Notably, Woese's elucidation of the tree of life shows the overwhelming diversity of microbial lineages: single-celled organisms represent the vast majority of the biosphere's genetic, metabolic, and ecologic niche diversity. As microbes are crucial for many biogeochemical cycles and to the continued function of the biosphere, Woese's efforts to clarify the evolution and diversity of microbes provided an invaluable service to ecologists and conservationists. It was a major contribution to the theory of evolution and to our knowledge of the history of life. Woese wrote, "My evolutionary concerns center on the bacteria and the archaea, whose evolutions cover most of the planet's 4.5-billion-year history. Using ribosomal RNA sequence as an evolutionary measure, my laboratory has reconstructed the phylogeny of both groups, and thereby provided a phylogenetically valid system of classification for prokaryotes. The discovery of the archaea was in fact a product of these studies". Evolution of primary cell types Woese also speculated about an era of rapid evolution in which considerable horizontal gene transfer occurred between organisms. First described by Woese and Fox in a 1977 paper and explored further with microbiologist Jane Gibson in a 1980 paper, these organisms, or progenotes, were imagined as protocells