Deep time is the dimension that marks out Geology from other sciences. The geological time scale is therefore fundamental to the subject, underpinning estimates of the ages of geological events and of the rates of Earth processes. The time scale is rightly regarded as the communal property of all geologists, but its stewardship has, in recent years, been entrusted to the International Commission on Stratigraphy (ICS). Four years ago, they were responsible for the major revision embodied in A Geologic Time Scale 2004 by Gradstein, Ogg & Smith. However, this comprehensive treatment was targeted at libraries and was beyond the needs and budgets of the average geoscientist. The new short version is aimed at this more general readership.
The Concise Geologic Time Scale embodies only a few well advertised modifications to the ages of stage boundaries since the 2004 version, and the main contrast is in the brevity of its presentation. The book comprises a chapter for each period of Phanerozoic time, preceded by an introduction and chapters on the planetary time scale and the Precambrian. Most of the Phanerozoic chapters have a standard format. First, there is a discussion of the international subdivisions of that system and a table of the relevant Global Boundary Stratotype Sections and Points (GSSPs). There is a photograph of the GSSP marking the base of the system. Then follows a graphic time scale for the period, with selected biostratigraphic schemes and sea-level curves. Some periods have a table of regional subdivisions correlated against the global chronostratigraphy. There is a brief discussion of selected aspects of the period's stratigraphy and a list of further reading and online references. Each chapter has one of Christopher Scotese's palaeogeographic maps as a frontispiece. The book concludes with a chart of the RGB colour codes for the whole time scale, and references for all the ratified GSSPs.
The 2004 time scale was such a weighty volume that it required some effort to ferry from bookshelf to desk, and more free desk space to consult than many of us can create. The 2008 volume is smaller and much thinner, and is a much more practical reference source, along with the enclosed pocket-sized laminated card of the time scale. Soft rather than hard covers would have been even more convenient. However, the book can be reliably recommended for any geologist who regularly refers to the time scale.
If The Concise Geologic Time Scale is not a best seller, then it will be because of another excellent recent product from the International Commission on Stratigraphy, well promoted in the book. This innovation is the online ‘TimeScale Creator’ database and chart-making package. The package is available free at www.stratigraphy.org, and probably points the way forward to the future updating and use of the time scale. It offers the exceptional convenience of being able to create chronostratigraphic charts for any selected time interval, with the choice of biostratigraphic and regional schemes, and of a wide range of sea-level and chemostratigraphic curves and the like. The charts can be exported as SVG files for use or modification in a graphics program. This self-service access to a constantly updated time scale will undoubtedly become the stratigraphic medium of choice for most geologists.
