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

• 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
• F. M. Gradstein, J. G. Ogg, and A. G. Smith. 2004. A Geologic Time Scale 2004 1-589 view

There are 12 timescales which overlap this one. show

• Obsolete Names for ICS Units
• Ten Million Year Bins
• Cambrian Epochs
• Ordovician of Britain
• Ordovician of the Baltic
• Ordovician of North America
• Cambrian of China
• Cambrian of Australia
• Cambrian of Siberia
• Cambrian of Kazakhstan
• Cambrian of North America
• Cambrian of West Avalonia

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 602 collections