Convergence of evidence on climatic change and ice ages [antikvár]

CONVERGENCE OF EVIDENCE ON CLIMATIC CHANGE AND ICE AGES Rhodes W. Fairbridge Department of Geology, Columbia University, New York, N.Y. Introduction Consideration of ideál meteorologic circulation patterns over an almost "smooth" globe of medium-depth seas and low continents of moderate dimensions indicates that the thermal balance would prohibit "ice ages." The efficiency of upper-atmospheric heat transfer is assisted by the more sluggish but stabilizing control of oceanographic currents. Even with the known perturbations of the solar spectrum, variations in the cosmic-ray emissions, and observed astronomic-mechanical controis, the geologically "normál" climatic history of the globe shows no evidence of ice ages through the betterknown rangé of the last 109 years except at certain specific times and places. Roughly speaking, those times were: Late Precambrian, 6 to 7 X 108 years ago. Place: Northern Hemisphere, Australia, South America, and South Africa; but not necessarily synchronously. Siluro-Devonian 3 to 4 X 108 years ago. Place: South America and South Africa. Permocarboniferous 2.8 X 108 years ago. Place: South America, South and central Africa, India, and Australia. Quaternary (Pleistocene) 5 X 105 years ago and still continuing. Place: North America, Greenland, Scandinavia, and Antarctica. It may be noted that, from the present (limited) data in Antarctica, there is no positive evidence for any ice ages prior to the Quaternary (Fairbridge, 1952), except for a recent report of possible Permian tillites in the Horlick Mountains. While the age ranges given are rather broad, the actual duration of glacial phases within any particular period is quite brief, probably not exceeding 0.5 to 1 X 105 years in any one instance. The recurrence of perhaps 50 to 100 such brief phases in 4 concentrated groups over a time span of 1 X 109 years suggests an "accidental" development or coincidence under an extremely low probability coefficient. In this paper it is submitted that ice ages are normál and predictable events under a long term sequence of observed variables in the physical history of the earth. The term accident is therefore intentionally used to indicate the rarity of certain events. Prior to the Cambrian, both in the late Precambrian and older than 1 X 109 years, there is widely scattered but poorly known evidence of glacial formations from every continent. There is no evidence that the glaciation was synchronous, so that its distribution could be explained by polar movements, numerous orogenies, and possible crustal displacements. However, the contemporary pattern of geochemical reasoning about the originál form and early evolution of the earth would ascribe a lowered temperature to early geologic time. The idea of a cool accretion from a low-temperature dust cloud (ca. 50° K)