Polar Wandering

22 Jan 2012

Sir Henry James in an article in a journal called The Athenaeum, in 1860, explained Ice Ages by the migration of the axis of rotation. The mechanism for this, he proposed, was the rapid elevation of the world's mountain chains which had disturbed the rotational balance. In fact, during the 19th century the idea of polar wandering was aired on many occasions - even during the early 20th century. It is rarely mentioned nowadays. 

James piece had a response by Sir George Airey, Astronomer Royal at the time, and he considered the physics and concurred in that he thought the mechanism was feasible but the forces required to bring it about were simply too great. Airey drew upon the work of mathematician Euler who had described the wandering of the axis of rotation within a rigid body of the Earth's mass. Airey thought a sudden elevation of a mountain chain by some unknown process would cause the axis to migrate and after an interval of wobbling (as described by Euler) the roation would settle at the new principle axis. However, Airey also thought it had never happened.

Paul Dunbavin, in his book Under Ancient Skies, Nottingham:2005 (available from the SIS book service) outlines the problems there are for the Poles to wander - but is convinced they did. Many geologists had noted, in the 19th century, that if the North Pole had been somewhere in the sea off Greenland this would account for the ice sheet as it was in the Last Glacial Maximum (variously the Wurm or Wisconsin glaciation). Peter Warlow was a more recent scientist to realise this might explain the actual ice coverage that ensued during the Wurm event (at the recent SIS Cambridge Conference). 

George Darwin, a geophysicist and son of Charles Darwin, used mathematical equations to counter the idea of polar wandering, and geophysicists since then have been happy to accept the consensus view that had built up - the Poles could not move. It was accepted that huge ice sheets built up in the northern hemisphere but it was much later that it was realised that ice was absent from Siberia and Alaska. Once Plate Tectonics was adopted it was used to explain geological anomalies before the Pleistocene Ice Ages, such as temperate and tropical climates inside the present Arctic Circle. Textbooks and consensus tub thumpers say it is impossible - but is it? Would the same people wedded today to the consensus view have not resisted the idea of Plate Tectonics when it was first aired. Why can't Plate Tectonics and Polar Wandering both be a reality?