ICS International Chronostratigraphic Chart 2024/12

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). Ratified Subseries/Subepochs are abbreviated as

U/L (Upper/Late), M (Middle) and L/E (Lower/Early). Italic fonts indicate informal

units and placeholders for unnamed units. Previous versions and detailed

information on ratified GSSPs are available at the website

http://www.stratigraphy.org. The URL to this chart is provided below.

Numerical ages are subject to ongoing revision and do not define units in the

Phanerozoic and the Ediacaran; only GSSPs do. For boundaries in the

Phanerozoic without ratified GSSPs or without constrained numerical ages, an

approximate numerical age (~) is provided.

Most numerical ages are taken from ‘A Geologic Time Scale 2020’ by Gradstein

et al. (2020), but some ages differ as provided by the relevant ICS

subcommissions, with advice from the Timescale Calibration subcommission.

These are approved by the ICS executive as the current consensus.