Final answer:
Carl Woese redefined the classification of life into three domains (Bacteria, Archaea, Eukarya) using genetic sequencing of ribosomal RNA genes, revealing deeper genetic relationships over morphological similarities.
Step-by-step explanation:
The work of American microbiologist Carl Woese in the early 1970s fundamentally changed our understanding of the phylogenetic tree of life. He proposed that all life on Earth has evolved along three lineages, which he classified into domains known as Bacteria, Archaea, and Eukarya. The first two domains consist of prokaryotes, which are single-celled organisms that lack membrane-bound nuclei and other organelles. In contrast, the third domain, Eukarya, encompasses all eukaryotic organisms, which do have membrane-bound organelles and a nucleus. This was a significant departure from the previous five-kingdom classification system that was based mostly on morphology. To establish these domains, Woese used a method of genetic analysis that focused on sequencing ribosomal RNA genes, providing a basis for reflecting evolutionary relationships rather than mere physical resemblance. Among the Archaea domain, a group of organisms known as extremophiles are notable for living under harsh environmental conditions.