This chart is based on the original drafted by G.Ogg (August 2009), and modified to be viewed vertically by A.R.T. Spencer.
Intra Cambrian unit ages with * are informal, and awaiting ratified definitions.
Subdivisions of the global geologic record are formally defined by their lower boundary. Each unit of the Phanerozoic (~542 Ma to Present) and the base of Ediacaran are defined by a basal Global
Boundary Stratotype Section and Point (GSSP), whereas Precambrian units are formally subdivided by absolute age (Global Standard Stratigraphic Age,
GSSA). Details of each GSSP are posted on the ICS website (www.stratigraphy.org).
Numerical ages of the unit boundaries in the Phanerozoic are subject to revision. Some stages within the Cambrian will be formally named upon international agreement on their GSSP limits. Most
sub-Series boundaries (e.g., Middle and Upper Aptian) are not formally defined.
Colors are according to the Commission for the Geological Map of the World (http://ccgm.free.fr/index_gb.html).
The listed numerical ages are from ‘A Geologic Time Scale 2004’, by F.M. Gradstein, J.G. Ogg, A.G. Smith, et al. (2004; Cambridge University Press) and “The Concise Geologic Time Scale” by J.G. Ogg, G. Ogg and F.M. Gradstein (2008).