Three-domain system

The three-domain system is a taxonomic classification system that groups all cellular life into three domains, namely Archaea, Bacteria and Eukarya, introduced by Carl Woese, Otto Kandler and Mark Wheelis in 1990. The key difference from earlier classifications such as the two-empire system and the five-kingdom classification is the splitting of Archaea (previously named "archaebacteria") from Bacteria as completely different organisms. The three-domain system has been contested by scientists who believe that eukaryotes do not form a separate domain of life, but instead represent a clade alongside the Archaea, in a single shared domain. A consensus had emerged that eukaryotes had evolved from within Archaea as traditionally defined (having affinities with Asgard archaea), rather than a separate sister grouping.