OHAP. 34] THE PLEISTOCENE RECORD 889 



Pleistocene research assumes an importance that vastly exceeds purely his- 

 torical interest. 



In the view of many, the Pleistocene is the last epoch of geologic time. It has 

 been defined as the time elapsed since the late Cenozoic migration of certain 

 species of northern marine mollusks and Foraminifera into the Mediterranean, 

 and is beheved to embrace many hundred thousand years. During this time 

 the history of the Earth has been particularly exciting and eventful. Most of the 

 Tertiary and some of the older mountain chains have been repeatedly uplifted, 

 with vertical displacements estimated in hundreds and, in some areas, thou- 

 sands of meters (cf. Flint, 1957, pp. 499-503). Volcanic activity has been 

 intense, as evidenced by great lava flows on many lands and by numerous and 

 widespread ash layers in deep-sea sediments (cf. Worzel, 1959). Vast ice sheets 

 have repeatedly covered large continental areas, especially in the Northern 

 Hemisphere. The whole biosphere has been subjected to intense environmental 

 stresses. Evolution, especially among land animals, has been generally fast and, 

 last but not least, man has come into being. 



Glaciation is the outstanding feature of the Pleistocene Epoch. Indeed, the 

 definition of the Pliocene-Pleistocene boundary implies climatic deterioration 

 that led to the general development of glaciers. Glaciation may have been 

 made possible by an increase in albedo accomjDanying mountain building 

 and uplift. The glaciers and pack ice that repeatedly spread over a third of 

 the Earth's surface caused a further large increase of albedo and consequent 

 temperature decrease. Within the last several hundred thousand years the 

 Earth has oscillated between glacial and interglacial conditions; that is, 

 between conditions of lower and higher temperatures. The temperature oscil- 

 lations have been greatest in the high latitudes, but have not been negligible 

 even at the equator. There is some reason to believe that the major temperature 

 oscillations have been world-wide and generally synchronous on the two polar 

 hemispheres (Emiliani and Geiss, 1959). If so, and if these oscillations are dated 

 absolutely, useful world-wide time markers would be available. Correlation with 

 the thermal record at any locality could then imply absolute dating as well. 

 This is significant because absolute dating, especially of terrestrial material, is 

 at present difficult or impossible to achieve for much of the Pleistocene Epoch. 



Before the invention of the piston corer for sampling deep-sea sediments 

 (Kullenberg, 1947), Pleistocene studies centred largely on continental features. 

 From these studies were recognized four or five major glaciations, some of them 

 having second-order oscillations, and separated by interglacial intervals. Dating 

 of glacial and interglacial events was based largely on geologic estimates of 

 dubious validity, until radiocarbon dating was developed. Ajiplication of this 

 method to continental material resulted, during the decade 1950-1960, in 

 fixing the last two major glacial maxima at about 18,000 years B.P. (before the 

 present) and about 60,000 years B.P. As the natural limitations of the radio- 

 carbon method preclude the dating of material older than about 70,000 years, 

 most of Pleistocene time is beyond the reach of radiocarbon. In addition, the 

 inherent discontinuity and fragmentary character of the continental record 



