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  • Christopher Scotese
Christopher Scotese
Northwestern University

Corresponding Author:[email protected]

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We live in an “Ice House” world that has extensive ice cover at both poles. However, it has not always been this way. During the last 540 million years there have been only 4 other time intervals characterized by extensive polar ice caps (latest Ordovician, latest Devonian, Permo-Carboniferous, and late Cenozoic). The combined duration of these frigid intervals was approximately 160 million years, or ~30% of Phanerozoic history. During the remaining 380 million years the Earth lacked permanent polar ice caps, though some winter snow and ice may have accumulated at high latitudes during cool, greenhouse intervals (Silurian-early Devonian, late Jurassic – early Cretaceous). The modern ice house world is probably the most severe of all ice house worlds because it is the only time in Earth history when the North and South polar regions were concurrently glaciated. Using the compilation of lithologic indicators of glacial conditions (tillites, dropstone, & glendonites) compiled by Boucot et al. (2013), I have mapped the areal extent of polar ice caps (millions of km2) for the time periods when ice house conditions prevailed. Using a simple algorithm that estimates the thickness of the ice based on the total area of the ice cap, I have calculated the corresponding volume of continental ice (millions of km3) for each of these time intervals. Converting solid ice to liquid water, the equivalent volume of evaporated ocean water was calculated. Expressed as a percentage of the present-day volume of ocean water (1.35 billion km3), I estimated the amount of water removed from the oceans during each of these ice house intervals. Preliminary results, indicate that the five largest ice volume events were the Hirnantian (444.5 Ma) – 2%, Modern World – 2%, Pliocene (3 Ma) – 2%, early Permian (280 Ma) – 1.5%, and late Miocene (10-15 Ma) – 1.4%. Since the water removed from the oceans by evaporation is preferential enriched in 16O, it is possible to calculate the resulting δ18O of the remaining oceanic reservoir. These calculations may be useful when estimating paleotemperatures from the δ18O record of fossil organisms.