This study presents the science community with a new geologic time scale for circa 3850 million years of Earth history. The scale encompasses many recent advances in stratigraphy, the science of the layering of strata on Earth. The new scale closely links radiometric and astronomical age dating, and provides comprehensive error analysis on the age of boundaries for a majority of the geologic divisions of time. Much advantage in time scale construction is gained by the concept of stage boundary definition, developed and actively pursued under the auspices of the International Commission on Stratigraphy (ICS), that co-sponsors this study.

It was in 1997 that Alan Smith approached two of us (F.M.G. and J.G.O.) with the request to undertake a new edition of A Geologic Time Scale 1989 (GTS89) for Cambridge University Press. This was just after the “Phanerozoic Time Scale” with the A3 format time scale colour chart as insert, sponsored by Saga Petroleum in Norway, had appeared in Episodes. Although we realized this new request was a tall order, we optimistically accepted. A proposal was formulated and improved through peer review. As with GTS89, the new edition of the book would not necessarily give the very latest developments in any field, but would present a balanced overview designed to be educational and useful for advanced university students.