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We find no vestige of a beginning, no prospect of an end. - James Hutton, Theory of the Earth (1795) This is a handy Geological Time Scale in correct linear scale. I originally drew it up for my own use. Those of you who know all that Triassic - Jurassic - Cretaceous stuff can skip this part. The names used for the times in which fossil creatures were in their pre-fossil state were originally applied to systems of rocks. However, for both fossils and rocks, the geological column makes a dandy time scale as well, once the dates during which the rocks were deposited are determined. Igneous rocks can be dated by radioactive decay, and sedimentary rocks can be dated if they are suitably bracketed by igneous rocks. This business of geology, stratigraphy, and rock systems is all more exciting than it may at first glance seem. For instance, the feud between Adam Sedgwick and Roderick Impey Murchison over the boundary of the Cambrian and Silurian rock systems is legendary, on a par with the later Bone Wars between Marsh and Cope. (The Royal Society got the last laugh over Sedgwick and Murchison in 1879, by appropriating the disputed rock systems and naming them the Ordovician.) To fit on the screen I've divided the chart into three. I tried a logarithmic scale, but results were not overly impressive, so I reverted to the conceptually simpler linear scale. The first of the three parts shows the Big Picture, from Creation to today. The second part expands the Phanerozoic eon of the first part, and extends from 570 million years ago to today. The third part expands the Tertiary period of the second part, and extends from 65 million years ago to today. The dates shown may not be the absolute latest hot-off-the-press revisions, but they'll do. Modern geology recognizes far more subdivisions than I've shown. A good source for all the details is A Geologic Time Scale, published by the Cambridge University Press. The first edition came out in 1982, and was authored by W. B. Harland, A. V. Cox, P. G. Llewellyn, C. A. G. Pickton, A. G. Smith, and R. Walters. It was revised and republished in 1990 as A Geologic Time Scale 1989, the authors this time around being W. B. Harland, R. L. Armstrong, A. V. Cox, L. E. Craig, A. G. Smith, and D. G. Smith. The latest (big, fat, and expensive) revision, A Geologic Time Scale 2004, by F. Gradstein, J. Ogg, and A. Smith, isn't out yet. I think I'll stick with the 1990 version, myself. Here it is, sized for you Luddites still using 800x600 pixel screens. Click on the image for a bigger version, suitable for 1280x1024 screens. 
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