International Chronostratigraphic Chart
The International Chronostratigraphic Chart shows the sequence of chronostratigraphic units and the numeric ages of their boundaries. Chronostratigraphic unit is a body of rocks that were formed in a specific time interval. Each unit is defined by its lower and upper boundary, both of which are isochronous horizons representing records of specific events in the Earth’s geological history. These horizons are objectively determinable and can be correlated globally. Chronostratigraphic units are hierarchically arranged from the lowest to the highest rank in the following order: Stage, Subseries, Series, System, Erathem, and Eonothem. Units of all ranks are in the process of being defined by Global Boundary Stratotype Section and Points (GSSP) for their lower boundaries, including those of the Archean and Proterozoic, long defined by Global Standard Stratigraphic Ages (GSSA). Italic fonts indicate informal units and placeholders for unnamed units. The International Chronostratigraphic Chart has been compiled and is continuously updated by the International Commission on Stratigraphy. The Czech translation was made by the Czech Stratigraphic Commission.