by Trevor » Sun 16 Dec 2012 5:52 pm
The information presented by Laurence is very interesting, but does it provide any reason to suppose that one or more crustal slips have occurred during the past 2,000 years? Ancient reports giving indications of the latitude and longitude of particular cities would only be meaningful in terms of making comparisons with the situation today if the methodology applied could have given reliable results, and if the system of co-ordinates used was made clear. How much do we know about Ptolemy's system of co-ordinates, and his methodology? The accurate determination of longitude in particular posed problems until the late 18th century, since it requires a knowledge of the precise difference between local time and the corresponding time at a specified reference point. The greatest problem was faced by sailors, since they had no way of accurately determining longitude until the invention of Harrison's marine chronometer in 1773. Sending out surveyors to determine the accurate latitude and longitude of foreign ports earlier in the 18th century would have been pointless, because sailors would have had no way of making use of this information. Even in the early part of the 19th century, few ships were equipped with accurate marine chronometers. Furthermore, there was no international agreement about the reference line for longitude determinations until 1884.
The forces required for a crustal slip to occur are immense. Admiral Flavio Barbiero has argued that they could be supplied by an asteroid impact at an appropriate angle, but that remains controversial. What is certain is that a crustal slippage, particularly one changing the positions of the poles, would have had catastrophic consequences, because the Earth is not a perfect sphere. Therefore, if a crustal slippage involving relocation of the poles had occurred during the past 2,000 years, there should be widespread evidence of catastrophic events, as well as changes of orientation, at this time. Can such a time be identified?