This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Numerous geologic time scales, both published and unpublished, are currently in use. None is considered the official or standard time scale. The U.S. Geological Survey's Suggestions to Authors (Hanson, 1991) presents a time scale but explains "other published schemes may be followed instead [...]; in any event, specify what scheme is being followed."
This report presents, in tabular format, a compilation of the age estimates assigned to the major time boundaries by several commonly used or readily available time scales. It is not an exhaustive collection and is provided solely as a means of comparison.
The author(s) of most time scales provide(s) references citing the source of the ages; those sources are not reproduced here. The user is encouraged to refer to the original source of whichever time scale(s) is(are) chosen for additional information about fossils, global variations, local usage, or provincial series names. Some time scales may be more suited to a particular time period than others.
Gradstein, F.M., and Ogg, James, 1996, Episodes, v. 19, nos. 1&2, p. 3-5.
Grant, Brian, 1999, The Art and Science of Writing Geoscience Reports: Toronto, Canada, Prospectors and Developers Association of Canada, 200 p., http://sites.netscape.net/geomanual/BG-Timescal-Oct99.pdf.
Hansen, W.R., 1991, Suggestions to Authors of the reports of the United States Geological Survey, 7th edition: Washington, D.C., U.S. Government Printing Office, 289 p. (fig. 15, p. 59).
Haq, B.U., and Van Eysinga, F.W.B., 1998, Geological Time Table, 5th revised edition: New York, Elsevier Science.
Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G., and Smith, D.G., 1990, A geologic time scale, 1989: Cambridge, U.K., Cambridge University Press, 263 p.
Palmer, Allison, 1983, The Decade of North American Geology 1983 Geologic Time Scale: Geology, v. 11, no. 9, p. 503-504.
Pan Terra, 1998, A Correlated History of Earth, 2nd edition: Hill City, South Dakota, Pan Terra, Inc., http://www.wmnh.com.
Topinka, Lyn, 2001, The Geologic Time Scale: U.S. Geological Survey, http://vulcan.wr.usgs.gov/Glossary/geo_time_scale.html.