Last modified: Sat 4/26/97 0330 PDT
 Canon Terms |
Object | Classes | EarthOrganism; Taxonomy; Taxon; TaxonomicRank; SuperdomainTaxon; DomainTaxon; SubdomainTaxon; SuperkingdomTaxon; KingdomTaxon; SubkingdomTaxon; SuperphylumTaxon; PhylumTaxon; SubphylumTaxon; SuperclassTaxon; ClassTaxon; SubclassTaxon; SuperorderTaxon; OrderTaxon; SuborderTaxon; SuperfamilyTaxon; FamilyTaxon; SubfamilyTaxon; SupertribeTaxon; TribeTaxon; SubtribeTaxon; SupergenusTaxon; GenusTaxon; SubgenusTaxon; SupersectionTaxon; SectionTaxon; SubsectionTaxon; SuperseriesTaxon; SeriesTaxon; SubseriesTaxon; SuperspeciesTaxon; SpeciesTaxon; SubspeciesTaxon; SupervarietyTaxon; VarietyTaxon; SubvarietyTaxon; SuperformTaxon; FormTaxon; SubformTaxon; Phylogeny; DomainEukaryota; DomainBacteria; DomainArchaea |
| Instances | (none) | ||
| Event | Classes | LifeCycle | |
| Instances | (none) |
Earth's organisms, both the living organisms and the fossil organisms found on Earth are the only organisms currently known to humans, although structures have recently been discovered in meteorites which some believe to be fossils which originated on Mars.
For nomenclatural purposes, all known kinds of Earth organisms are classified conventionally within a hierarchical structure of superclasses and subclasses known as a taxonomy. Each category (class) of Earth organisms in the taxonomy is referred to as a taxon (plural taxa). The taxonomic study of Earth organisms is the subject matter of systematic biology, also called biosystematics.
A taxonomy is structured at several taxonomic ranks, each successive rank being less general (the subclass) than the one before (the superclass), with the taxa at the top rank subsuming all kinds of Earth organisms. Some ranks are seldom used, and there is probably no Earth organism that is classified (or needs to be classified) at every rank.
The ranks used for classifying all Earth organisms are given in the table below. The ranks shown as bright, medium and dark green are primary, secondary and tertiary ranks, respectively, according to the degree to which the rank is commonly used for the organization of taxa.
The most fundamental taxonomic rank is that of species (for which there is, however, no single definition that is universally accepted). There may be as many as 100 million living and fossil species of Earth organisms, with new species being identified on a routine basis.
It is observed that all organisms of a species have certain essential aspects of their behavioral trajectories in common, referred to as that species' life cycle.
When taxa are defined on the basis of evolution, i.e. the process of progressive divergence among the genomes of organisms over time), the resulting taxonomy is called a phylogeny (or phylogenetic taxonomy). The study of phylogenetic taxa is the subject matter of phylogenetic biology (sometimes called phylobiology), part of biology.
Earth's organisms are currently considered to be subsumed exhaustively under three domains: Eukaryota, Bacteria and Archaea.