Summary

Abstract

Summary Until the recent publication of radiometric dates for (i) the Eifel volcanic rocks, (ii) sediments from deep-sea cores, (iii) shells from high shore-lines, and (iv) polarity changes in Pleistocene volcanic rocks, there was no adequate basis for a Pleistocene time-scale. For example, dates proposed for the beginning of the Mindel glaciation range from 200 to 1450 thousand years ago. This review attempts a synthesis of the chronological evidence for Pleistocene events, with the main emphasis on the part older than the radiocarbon limit. Palaeomagnetic evidence from deep-sea cores and the mid-oceanic ridges is used to supplement the time-scale for geomagnetic reversals published by Cox et al. (1968), and attention is drawn to the uncertainty of the date shown by deep-sea cores for the beginning of the Brunhes normal epoch. Discussion of climatic evidence that can be dated palaeomagetically shows that there is no evidence of any major deterioration in climate which can be taken as the beginning of the Pleistocene. The most convenient Plio-Pleistocene boundary based on palaeontological changes has an age of slightly over two million years. In deep-sea cores, the proportions of the isotope 18 O in foraminiferal shells, the relative abundance of some temperature-sensitive foraminifera, and differences in the amount of coarser constituents in the sediments, together provide a record of cyclic changes in climate. Radiometric dating shows that these changes have a somewhat irregular period averaging about 40 000 years. Variations in the Earth’s relationship to the Sun bring about changes in insolation which in higher latitudes