Microbes are responsible for many biogeochemical cycles and are crucial to the continued function of the , Woese's efforts to clarify the evolution and diversity of microbes provided an invaluable service to ecologists and conservationists.

Woese’s big idea is that primitive life existed as a community of cells that freely exchanged genes. They shared a basic translation system for making proteins, but had little else in common. These cells evolved as a community and not as distinct lineages. Before Woese, the tree of life had two main branches called prokaryotes and eukaryotes, the prokaryotes composed of cells without nuclei and the eukaryotes composed of cells with nuclei.