by Trevor » Thu 27 Dec 2012 8:55 pm
I welcome the recent responses by Peter and Phillip, but may I make a few comments.
Firstly, my recent posting pointed out the impossibility of obtaining accurate longitude determinations at sea before the late 18th century, but perhaps I should also have made it clear that the situation regarding land-based estimates was little better. In AD 1541, the Spanish empire gave great priority to the determination of the longitude of Mexico City (relative to the base line of Toledo in Spain), but the investigators appointed arrived at a value for the difference in longitude between these cities which exceeded the true figure (at least as it is today) by 26%. That can't be taken to indicate an axial shift or crustal slip since 1541, because even if Mexico City had been exactly due west of Toledo in 1541, making the difference in longitude between the cities the maximum possible for the distance between them, that would only have given a value 2% greater than the present one. The investigators undoubtedly made a major error.
As Peter has correctly said, the situation regarding latitude was not as problematical as that concerning longitude. However, there was still a range of uncertainty. Charles Hapgood, the main originator of the theory that there had been a very significant crustal dislocation within relatively recent times, noted in his 1966 book, "Maps of the Ancient Sea Kings", the well-established historical difficulties of making accurate determinations of longitude, and added, "The case for latitude is somewhat different. Latitude could be determined in the 15th and 16th centuries by astronomical observations", but he then went on to write, "However, observations taken by trained people with proper equipment were one thing, and observations taken by explorers were quite another". Hapgood was particularly critical of the early explorers of the western Atlantic. Let us therefore take a look at the information provided by these explorers during the late 15th and early 16th centuries. A summary by Peter of the maps produced in this period, as well as quotations from the letters of Christopher Columbus, was published in Review 2008 pp. 11-12.
The AD 1500 map by Juan de la Cosa indicated the Tropic of Cancer running south of Hispaniola and Cuba, as did the 1502 map of Alberto Cantino, whereas today it runs north of Hispaniola and just brushes the northern fringe of Cuba. The map of Bartholomew Columbus, generally dated to 1506, similarly located the Tropic of Cancer south of Hispaniola, but completely omitted Cuba, the largest island in the Caribbean. The 1507 global-gores of Martin Waldseemuller placed the Tropic of Cancer south of both Hispaniola and Cuba, whereas Waldseemuller's world-map dating from the same year, although locating the Tropic of Cancer south of Hispaniola, had the same line of latitude running through the middle of Cuba. The 1508 map by Francesco Roselli (given in Review 2008 as "Rosselini") showed the Tropic of Cancer running south of both Hispaniola and Cuba, whereas the map by Johannes Ruysch, also from 1508, showed the Tropic of Cancer running south of Hispaniola but brushing the southern coast of Cuba.
Two decades later, the 1526 map by Juan Vespucci and the 1528 map by Benedetto Bardone both showed the Tropic of Cancer running through Cuba but passing north of Hispaniola, whereas the 1527 map by Robert Thorne showed the Tropic of Cancer passing north of both Hispaniola and Cuba, in line with the situation of the present day.
Two main scenarios are possible. One is that either an axial shift or a crustal displacement took place during the early 16th century; the other (and to my mind the more plausible one) is that there was a rapid advance in geographical knowledge about the Caribbean region during that period, allowing earlier mistakes to be corrected. We know very little about the origin of the information on which the world maps of the first decade of the 16th century were derived, but it seems clear from the difference between the crude sketches from the period between 1500-1510 (showing, as Hapgood pointed out, considerable variations in relative distances and land-shapes, without any evidence of the use of trigonometry by the explorers) and the much more detailed ones from 20 years later, that significant advances had taken place. In any case, had an axial shift or crustal displacement taken place early in the 16th century, it would have led to changes of latitude throughout the world, not just in the Caribbean. Is there any evidence that the latitude of, say, London or Paris, changed at this time?
Turning to Phillip's queries, Wegener's arguments about continental drift were ignored during the first half of the 20th century largely because he was unable to suggest a plausible mechanism, but the plate-tectonic model proposed by the Princeton geologist Harry Hess, a friend of Velikovsky, provided one, suggesting that continental plates could be pushed around over the top of the Earth's mantle as a consequence of activity involving oceanic plates. Newly-formed oceanic crust would spread out under the seas from mid-ocean ridges and old oceanic crust would eventually disappear, by subduction, back into the interior of the Earth. According to plate-tectonic theory, the situation would keep changing because of interactions between existing plates and also the emergence of "hotspots" from the interior of the Earth, to become new centres of sea-floor spreading. Also, as configurations of plates changed, sea-levels throughout the world might rise or fall in consequence. A configuration in which, in overall terms, oceanic crust was being recycled relatively rapidly would lead to a general upward movement of sea-floors and hence a general rise in sea-levels, and vice-versa. Tectonic effects could also lead to an apparent change in sea-level in a particular locality, because of the elevation or sinking of land relative to the sea. Regardless of tectonic effects, world-wide increases in sea-level could occur because of the melting of ice-sheets following a glacial period, and, more locally, there could also be apparent changes in sea-level after the end of a glacial period because of the "rebound effect".
There seems little reason to doubt that the tectonic-plate theory is based upon strong foundations. There is, for example, the evidence of sea-floor bands of alternate polarity spreading out from the mid-Atlantic ridge. There is also the geological evidence around Thingvellir in Iceland, showing the separation of the North American plate from the Eurasian one, as well as the geological and biological evidence from North America and Europe which shows that these continents were once linked together. However, many of the details are still far from certain. Timescales are generally
worked out on the assumption that the rates of continental drift in the past could not have been significantly different from those which can be measured today, i.e a few centimetres per year, but does that necessarily follow? On the basis of the uniformitarian approach, it is supposed that North America began to separate from Eurasia about 80 million years ago, and that that the Atlantic Ocean has widened by only a little more than a kilometre since the end of the last Ice Age. However, is it possible that a major catastrophic event at some point in the past could have caused an episode of much more rapid continental drift? That could only be speculation at the present time, but it may be something that can't be entirely ruled out.