Organism or group
Bacteria
Small single-celled organisms without a nucleus, found almost everywhere on Earth. Most bacteria in the human body are harmless, and some are helpful.
Three domains of life
Comparing ribosomal RNA divides life into three domains: Bacteria, Archaea and Eukarya.Source: Woese et al., 1990Source: Woese & Fox, 1977
Idea or model
How Three domains of life connects
Three domains of life describes
Organism or group
Archaea
Single-celled organisms without a nucleus that form a separate domain of life from bacteria.
Three domains of life is described by
Idea or model
Common ancestry
All known cellular life is thought to descend from a last universal common ancestor. Researchers infer its features from genes shared across life, and the details are still debated.
Studied in
Your progress
Sources & further reading
The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.
Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya (opens the original in a new tab)
Woese CR, Kandler O, Wheelis ML (1990). Proceedings of the National Academy of Sciences 87:4576-4579.
Peer-reviewedPerspectivePhylogenetic structure of the prokaryotic domain: the primary kingdoms (opens the original in a new tab)
Woese CR, Fox GE (1977). Proceedings of the National Academy of Sciences 74:5088-5090.
Ribosomal RNA comparisons revealed the archaea as a separate lineage.
Peer-reviewedPrimary research