GEOLOGICAL RECORD ON THE OCEAN FLOOR 137 



as reflected by the paleotemperature in Atlantic sediments, with 

 the periodic changes in distribution of solar radiation over the 

 earth, postulated by Milankovic as responsible for the glaciations. 

 The time lag observed between temperature minima and the 

 maximum extension of continental ice sheets has recently been 

 explained by Emiliani and Geiss (1959) on the basis of plastic flow 

 of the ice. With the more accurate measurements of geological age 

 in the range of a few hundred thousand years that are promised 

 by the ionium-thorium method which is now being perfected by 

 Goldberg and co-workers, and by the protactinium method which 

 is being developed by Rosholt, Sackett, and Koczy it should be 

 possible to check Emiliani's theory accurately. 



In spite of our still limited knowledge of the sediments covering 

 the deep ocean floor and in spite of the ambiguities attached to 

 the time scales, which so far have been extrapolated from carbon- 14 

 measurements in the surface layer, it is probably right to say that 

 our best quantitative information about the climatic evolution of 

 the earth during the last million years comes from the oceanic 

 record. An exception has to be made for the last 20,000 years, 

 which are known in greatest detail from continental sediments, 

 where the record has in this case not been disturbed by later 

 catastrophic events. 



Among recent geophysical hypotheses, inspired by observations 

 on the deep ocean floor must also be mentioned the one proposed 

 by Ewing and Donn (1956) attempting to explain the climatic 

 oscillations in our geological period, and their commencement 

 about a million years ago. Ewing and Donn were impressed by the 

 indications in Atlantic cores of sudden transition from low surface 

 water temperatures, typical of the glacial ages, to the conditions 

 prevalent now and during interglacial ages. They assume that the 

 location of the pole in the Arctic basin gives rise to a climatic 

 instability and self-sustained oscillations. An originally ice-free 

 Arctic Ocean, freely exchanging water with the Atlantic would be 

 an efficient source of moisture in the Arctic region, causing growth 

 of the continental ice sheets. The tying up of water in these ice 

 sheets, however, would lower the sea level to near the sill depths 

 of the Arctic basin, and the lowered influx of warm, Atlantic water 



