Each claim states how it is known and cites its evidence.
EstablishedChronostratigraphic units are rock; geochronologic units are time. Each has a counterpart in the other.
General principle, shown here for context — not an observation about this record.
Chronostratigraphic units are bodies of rock defined between specified stratigraphic horizons representing intervals of geologic time; the intervals of time themselves are geochronologic units. A system is a body of rock, a period is a length of time.
- generality: GENERAL_PRINCIPLE
Evidence support: Supported by the cited evidence · one source
Evidence: International Commission on Stratigraphy n.d. · Primary authority
EstablishedA shared reference frame for narrating Earth history.
General principle, shown here for context — not an observation about this record.
The purpose of chronostratigraphic classification is to organise the rocks of the Earth’s crust into named units representing intervals of geologic time, to serve as references in narratives about Earth history.
- generality: GENERAL_PRINCIPLE
Evidence support: Supported by the cited evidence · one source
Evidence: International Commission on Stratigraphy n.d. · Primary authority
EstablishedBoundaries are defined by physical reference points in rock (GSSPs), not by numbers.
General principle, shown here for context — not an observation about this record.
A stage includes all rocks deposited between two chronostratigraphic horizons defined by Global Boundary Stratotype Sections and Points; the stage is the lowest-ranking unit that can be recognised globally, and its boundary stratotypes also define the boundaries of the higher-ranking units built from it.
- generality: GENERAL_PRINCIPLE
Evidence support: Supported by the cited evidence · one source
Evidence: International Commission on Stratigraphy n.d. · Primary authority
Established538.8–0 Ma before present
On the International Chronostratigraphic Chart (v2024/12), the Phanerozoic spans 538.8 to 0.0 million years before present.
- definition basis: International Chronostratigraphic Chart v2024/12; the chronostratigraphic counterpart of the Phanerozoic is the Phanerozoic Eonothem.
- precision note: The chart states that numerical ages are subject to ongoing revision and do not define units; GSSPs do.
Evidence support: Supported by the cited evidence · one source
Evidence: Cohen 2024 · Primary authority
EstablishedSystem/period, series/epoch, subseries/subepoch, stage/age.
General principle, shown here for context — not an observation about this record.
The formal hierarchy pairs each chronostratigraphic rank with a geochronologic equivalent: system with period, series with epoch, subseries with subepoch, and stage with age.
- generality: GENERAL_PRINCIPLE
Evidence support: Supported by the cited evidence · one source
Evidence: International Commission on Stratigraphy n.d. · Primary authority