Climate Since the 

 Late Cretaceous 



H. D. MacGinitie 



Humboldt State College, Areata, California 



r ast climates and their changes comprise one 

 of the most fascinating subjects in science, since climates have so 

 profoundly affected the evolution and distribution of life on the 

 surface of the earth. Of one conclusion we can be sure: as we turn 

 back the pages into the past, we see that world climates were 

 greatly different from those of today. In order to appreciate just 

 how different, we have to clear the cobwebs of the present entirely 

 out of our minds. Some time ago when I was discussing with a well- 

 known western botanist the fossils of Melasequoia and its associates 

 found in the far north — the McKenzie basin, Greenland, the Arctic 

 Islands, and Alaska — I was astonished at his remark, "Why, how 

 could they grow there in all that ice and snow?" His thinking was 

 tied to present conditions. Another conclusion we can be sure of, 

 in thinking about past climates, is that the conditions of the Recent 

 and Pleistocene have been most unusual in the history of the world. 

 Our present combination of widely emergent and elevated conti- 

 nents, lofty mountain ranges, and polar glaciation has probably 

 existed (with recurrences in the past) for less than one-fiftieth of 

 geologic time. 



As an illustration of the misconceptions that can result from 

 picturing the past too closely in terms of the present, here is a brief 

 quotation from a discussion of fossil arctic floras in a paper on the 

 evolution of plant associations (Mason, 1947, p. 206): 



An earth, tilted on its axis relative to the plane of its orbit, will inevita- 

 bly be characterized by a darkened polar area that will alternate season- 

 ally with a lighted condition. The duration of the darkness will vary to 

 some extent with position but will range from a few days of total darkness 

 to almost six months of total darkness. By total darkness I mean the 



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