 The molecular clock is but one of many examples of the importance of molecular biology to phylogenetics. Importantly, incorporating molecular data helped extend phylogenetic studies beyond eukaryotes, i.e., the molecular revolution has fundamentally altered (or, arguably, created) the field of microbial phylogenetics. Beginning in 1969, Carl Woese began to sequence ribosomal RNA (rRNA) from across the prokaryotic kingdom in an effort to understand bacterial phylogeny. The work was slow and difficult, but by 1975 Woese and his lab had sequenced the rRNA of 27 different bacterial taxa (Woese et al. 1975). In 1977, Woese and George Fox dropped a bombshell. They had sequenced genes from a number of prokaryotic organisms whose rRNA genes lacked the standard signatures of all previously known bacterial rRNA genes and which appeared as distantly related to the bacteria as did the eukaryotes. Woese and Fox named them the “Archaebacteria” to emphasize their distinctness (Woese &amp; Fox 1977). In 1990, Woese, Kandler, and Wheelis (1990) produced the first attempt at building a universal tree of life that included bacteria, archaebacteria, and the eukaryotes based on molecular data, with the project continuing to this day (Ciccarelli et al. 2006; Hinchliff et al. 2015; Hug et al. 2016). All of this is only possible because of molecular sequence data.