What is the Three-Domain System?
The three-domain system is a method for classifying cellular life which was initially proposed by Carl Woese in 1990. While the three-domain system met with some initial opposition, it has since become widely accepted, thanks to scientific discoveries which have supported Woese’s proposal. Under the three-domain system, all cellular life can be divided into three domains: Archaea, Bacteria, and Eukaryota, and each domain can be further divided into kingdoms, phyla, classes, and so forth. This classification system distinguishes between eukaryotic organisms, organisms which have cells which include a nucleus, and two types of prokaryotic organisms, organisms with cells which lack a nucleus. Initially, Archaea and Bacteria were both lumped together as prokaryotes, although each group had its own kingdom. Woese argued that Archaea and Bacteria were so distinct that they actually belonged in separate domains, not just separate kingdoms. The differences between Archaea and Bacteria primaril
