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Evidence from the coast of Devon Looking for the Ice Age Shore Line Magnetic Reversals and Crustal Overturn Evidence from the coast of Devon |
Overturn - ending the ice ageOverturn is a rare event in the earths history, but fundamental to explaining the ice ages. Ice was building up at the poles, miles thick. Because the poles were on the edge of continental masses this buildup was eccentric.
The earths crust cannot sustain an eccentric mass on the axis of rotation, but the crust is plastic enough to deform as the ice accumulates - slowly, year by year, for thousands of years. However this will exert pressure on adjacent crustal plates, and these will drift in response to these eccentric pressures. However, under the ice sheet are volcanoes and lakes. Should the glaciers start to flow more rapidly in response to an under ice erruption, the outflow can be dramatic and catastrophic. The collapse of an ice sheet two miles thick can throw the balance of mass of the earths crust around the axis of rotation of the earth into a sudden imbalance. The crust cannot rotate out of balance - it must move - and once started it will move until friction between the plates is greater than the imbalance of forces created by movement of the ice. This can at its least dramatic move the poles by a few hundred miles, before sticking. The slow process of deformation and build up of ice starts again. But at the end of the ice age the imbalance was far more dramatic, and the result was complete overturn. All the crustal plates rotating round an axis that runs from off the west coast of Africa to the middle of the Pacific.
The evidence for these tumultuous events is clear. Great ocean trenches clear of sediment as they have been created too recently for the sediment to accumulate. Banks of sea shells high in the Andes match those of the present day shores, and salt lakes still with marine life from the coastal lagoons up high in the mountains. Mamoths frozen by an arctic winter, that were eating leafy plants in a temperate summer. The great barrier reef of Australia that only started developing when the ice age ended. The planets bio-diversity hot spots remain in those climate zones where the climate before the overturn was close to the climate after the overturn. Where the climate change was greatest, many species have died, or remain today living at the limits of their ability to survive. This information is copyright Peter Thomson 2001-2004 The following files on this site match your querySearch for any topic in this forumMore pages or to contribute to the discussion- look at the list in the main index.
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