For international maps or small-scale maps (for instance, 1:5 million) of the United States or North America, the GNC recommends use of the international (CGMW) colors. C., and the Subcommission on Quaternary Stratigraphy, 2010, Formal ratification of the Quaternary System/Period and the Pleistocene Series/Epoch with a base at 2.58 Ma: Journal of Quaternary Science, v. Specifications for the USGS colors are in the Federal Geographic Data Committee, Geologic Data Subcommittee (2006) guide, and those for the CGMW colors are in Gradstein and others (2004). Although the Tertiary is not recognized by many international time scales, the GNC agrees that it is important that it be recognized as a system/period; the map symbols "T" (Tertiary) and "Q" (Quaternary) have been used on geologic maps for more than a century and are widely used today. Another change to the time scale is the age of the base of the Holocene Series/Epoch. This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.Advances in stratigraphy and geochronology require that any time scale be periodically updated. 1) is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates. Divisions of Geologic Time shows the major chronostratigraphic (position) and geochronologic (time) units; that is, eonothem/eon to series/epoch divisions. This fact sheet is a modification of USGS Fact Sheet 2007-3015 by the U. Scientists should refer to the ICS time scale (Ogg, 2009) and resources on the National Geologic Map Database Web site ( for stage/age terms.
Orndorff (chair), Nancy Stamm (recording secretary), Steven Craigg, Lucy Edwards, David Fullerton, Bonnie Murchey, Leslie Ruppert, David Soller (all USGS), and Berry (Nick) Tew, Jr. Advances in stratigraphy and geochronology require that any time scale be periodically updated. Geological Survey (USGS), State geological surveys, academia, and other organizations have sought to create a consistent time scale to be used in communicating ages of geologic units in the United States. Therefore, Divisions of Geologic Time, which shows the major chronostratigraphic (position) and geochronologic (time) units, is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates. Many international debates have occurred over names and boundaries of units, and various time scales have been used by the geoscience community. R., comp., 1983, The Decade of North American Geology [DNAG] 1983 geologic time scale: Geology, v. Also of note, the Ediacaran is the only formal system in the Proterozoic. B., van, eds., 1998, Geological time table (5th ed.): Amsterdam, Elsevier, 1 sheet. All other units are periods until global boundary stratotype sections or points are defined. The "North American Stratigraphic Code" (North American Commission on Stratigraphic Nomenclature, 2005) recommends abbreviations for ages in SI (International System of Units) prefixes coupled with "a" for "annum": ka for kilo-annum (103 years); Ma for mega-annum (106 years); and Ga for giga-annum (109 years).