Published online by Cambridge University Press: 01 May 2009
Relevant points of general principle and special application to the problem under discussion are quoted selectively from the recently published time scale by Harland et al. (1982) and critically considered. Most of the principles and the resulting names for divisions of the Precambrian–Cambrian transition used in it are accepted. The unique significance of the transition from dominantly chronometric to dominantly chronostratic boundaries based on the ‘biostratigraphic sequence’ is an additional justification for the higher ranks previously given to the Vendian (Era) and its constituent divisions: Varangian (or Varangerian) and Ediacaran (or Ediacarian) Periods. The historic transition begins with the latest of the Proterozoic glaciations (the earlier ones started about 950 m.y. ago) and ends with the exponential diversification of the Metazoa. The causal linkage of the two events is hypothetical. Their stratigraphic sequence is demonstrable on the East European platform where the type section of the Vendian is located, and on the Yangtse platform. Normative, operationally designated boundaries are required for the stratigraphic divisions. The history of life in which there are no sharp initial and terminal boundaries shows clearly a rapid transition from widespread but generally rare occurrences of Vendian, particularly Ediacaran, fossils to ubiquitous, generally ‘shelly’ Palaeozoic (initially Cambrian) faunas of unquestioned biostratigraphic importance. This biohistoric transition is the beginning of the Phanerozoic division of a unique historic process. For the Eon of the stratigraphic scale comprising Palaeozoic to Cainozoic Eras the new term Holozoic is therefore proposed.