The interval definitions in this timescale are derived from the following sources:

• K. M. Cohen, S.C. Finney, P.L. Gibbard and J.-X. Fan. 2023. The ICS International Chronostratigraphic Chart v2023/09. view
• W. B. Harland, R. L. Armstrong, A. V. Cox, L. E. Craig, A. G. Smith and D. G. Smith. 1990. A Geologic Time Scale 1989. view
• F. M. Gradstein, J. G. Ogg, M. D. Schmitz and G. M. Ogg. 2020. Geologic Time Scale 2020 view
• B. D. Webby. 1998. Steps toward a global standard for Ordovician stratigraphy. Newsletters in Stratigraphy 36:1-33 view
• F. M. Gradstein, J. G. Ogg, and A. G. Smith. 2004. A Geologic Time Scale 2004 1-589 view

There are 59 timescales which overlap this one. show

• Cenozoic Subepochs
• Obsolete Names for ICS Units
• Ten Million Year Bins
• Mesozoic Subages
• Cretaceous Subepochs
• Carboniferous Subepochs
• Devonian Subages
• Cambrian Epochs
• European Faunal Units
• European Faunal Zones
• Mammal Paleogene Zones
• Cenozoic Subepochs of Southern Europe
• Central Paratethys Stages
• Neogene Mammal Ages of China
• Paleogene Mammal Ages of Asia
• North American Land Mammal Ages
• North American Mammal Subages/Zones
• South American Land Mammal Ages
• Cretaceous North American Land-Mammal Ages
• Ammonite Chrons of Northwest Europe
• Ammonite Chrons of North America
• Permian of the Russian Platform
• Permian of the Pamirs
• Permo-Triassic Subages of Eastern Europe
• Permian Subages of Germany
• Permian of Western Europe
• Permian of the Salt Range
• Permian of China
• Permian of North America
• Carbo-Permian of the Russian Platform
• Carboniferous of Western Europe
• Carboniferous of China
• Obsolete Carboniferous Ages of China
• Carboniferous of North America
• Devonian of France
• Devonian of Germany
• Devonian of Czechoslovakia
• Devonian of Eastern North America
• Silurian of the Baltic
• Silurian Ages of Europe
• Silurian of England
• Silurian of North America
• Ordovician of Britain
• Ordovician of the Baltic
• Ordovician of Ibero-Bohemia
• Ordovician of Australia
• Ordovician of China
• Ordovician of North America
• Cambrian of China
• Cambrian of Australia
• Cambrian of Siberia
• Cambrian of Kazakhstan
• Cambrian of North America
• Cambrian of West Avalonia
• Cambrian of Britain
• Precambrian of Russia
• Obsolete Precambrian Ages
• Cretaceous-Cenozoic of New Zealand
• Permian-Jurassic of New Zealand

Interval boundaries marked with * have been interpolated based on the differences between the ages for international timescale boundaries quoted in the source and the currently accepted ages for those boundaries.

Interval names marked with † are no longer in current use.

This timescale is used in the definition of 127252 collections