Ever since time scale charts have become wallpaper items in geological offices the world over, color of stratigraphic units has been a “hot” topic. Colors stir the senses, imagination, and also indignation. In this respect, the senior editor (FMG) of this book recalls strong emotional reactions of colleagues when he innocently tried to adopt the logical, pragmatic, and easily reproducible spectral color scheme in use with the US Geological Survey for an early version of the Gradstein and Ogg (1996) wall chart, courtesy of Saga Petroleum. He had to backtrack to so-called standard colors, i.e. Harland et al.'s (1990) emulation of the cryptic UNESCO color scheme.

Since there is consensus among geologists that the stratigraphic color scheme should be a reproducible and practical one, we will dwell on this issue below. At the end, our choice of colors will be made clear.

There are several well-known time scale charts in circulation, e.g.

1. A Geologic Time Scale 1989 sponsored by BP for Harland et al. (1990).

2. The A3 format and hand-held plasticized card of the Geological Time Scale by Gradstein and Ogg (1996) in Episodes.

3. The fifth edition of the Geological Time Table (Haq and van Eysinga, 1998).

4. […]