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Geological Society, London, Special Publications; 1964; v. 1; p. 29-36;
DOI: 10.1144/GSL.SP.1964.001.01.05
© 1964 Geological Society of London

Part 1: Introduction

A review of recent Phanerozoic time-scales

N. J. Snelling, M.SC., PH.D., F.G.S.

Age Determination Unit, Overseas Geological Survey, Department of Geology and Mineralogy, Parks Road, Oxford

The development of the K-At and Rb-Sr methods of age-determination together with a re-evaluation of the stratigraphical position of critical specimens used by Holmes when constructing his 1947 time-scale indicated the need for a revision of this scale. Holmes published a revised time-scale in 1959, but the latest and most comprehensive revision was published by Kulp in 1961. This paper summarizes the evidence used by these and other authors in dating the limits of the geological periods. The beginning of the Cambrian period was set at about 600 m.y., the end of the Palaeozoic era at 230 m.y. (Kulp 1961) and 250 m.y. (Holmes 1959), and the end of the Mesozoic era at 63 m.y. (Kulp) and 70 m.y. (Holmes).