The Origin of Continents and Oceans/Chapter 7
CHAPTER VII
GEODETIC ARGUMENTS
The displacement theory possesses the advantage over all other theories, with similarly far-reaching ideas, that it can be proved by accurate astronomical determinations. If continental displacements were active throughout such long periods of time, it must be assumed that they are continuing even at the present day. There thus remains only the question as to whether the movements are fast enough to be disclosed by astronomical measurements taken within a not too long period. We must go somewhat into the absolute duration of the geological periods in order to obtain a decisive opinion on this matter. The evaluation of these is, as is well known, very uncertain, but nevertheless, as a whole it does not render an answer to our question impossible.
The lapse of time since the last glacial period has been estimated by A. Penck, from his glacial studies on the Alps, at 50,000 years; by Steinmann, as at the least 20,000, and at the most 50,000 years; and by Heim, from his more recent calculations in Switzerland, and from the glacial geology of the United States, at only about 10,000 years. Milankovitch, by mathematical means, arrived at a climatic maximum cold of the last glacial period at about 25,000 years ago, and a climatic optimum (or climax of inter-glacial mild temperature, which the Swedish geologists claim to have existed), 10,000 years ago. De Geer concluded, from his counting of the bands of loam, that the retreating margin of the ice passed Schonen 12,000 years ago, but still lay at Meklenburg 14,000 years ago. The agreement between these figures is quite sufficient for our purpose.
For the older periods the thickness of the sediments yields an idea of the length of time of their deposition, and thereby, for example, a period of the magnitude of 1 to 10 million years for the Tertiary has been obtained.[1] But the greatest authority certainly pertains to the somewhat similar values derived from the estimation of the age of the rocks by physical means from their helium content. The helium is formed by the disintegration of radioactive substances. The measurements are carried out on zircon crystals, the helium content of which is produced by the breaking down of uranium. Strutt, who developed this method, found for the Oligocene 8.4, for the Eocene 31, for the Carboniferous 150, and the Archæan 710 million years. Königsberger[2] has revised the measurements of Strutt and determined other ages for some of the strata examined. The following periods of time are obtained from his and earlier data:—
- 500 million years have elapsed since the beginning of the Palæozoic.
- 50 million„ years have„ elapsed„ since the„ beginning„ of the„ Mesozoic.
- 15 million„ years have„ elapsed„ since the„ beginning„ of the„ Tertiary (Lower Eocene).
- 10 million„ years have„ elapsed„ since the„ beginning„ of the„ Eocene.
- 8 million„ years have„ elapsed„ since the„ beginning„ of the„ Oligocene.
- 6 million„ years have„ elapsed„ since the„ beginning„ of the„ Miocene.
- 5002–4 million„ years have„ elapsed„ since the„ beginning„ of the„ Pliocene.
- 1 million„ years have„ elapsed„ since the„ beginning„ of the„ Pleistocene.
- 10–50 thousand „have elapsed„ since the„ beginning„ of the„ Post-Pleistocene.
By the aid of these figures and the routes taken by the continents, we can obtain without much difficulty an approximate value for the annual displacement to be expected. Unfortunately, these figures are very uncertain, for the exact moment at which the blocks have separated can only be estimated at the best in a very inexact manner. It is therefore only to be expected that many of these figures will undergo much alteration in the future. Meanwhile I have obtained the values which are grouped in the following table:—
| Distance travelled. |
Since Separation, Millions of Years, approximately. |
Annual Movement. | |||
| Km. | Metres. | ||||
|
1070 | 0.05–0.1 | 21–11 | ||
|
920 | 0.05–0.1 | 18–9 | ||
|
1780 | 0.05–0.1 | 36–18 | ||
|
790 | 0.05–0.1 | 16–8 | ||
|
2410 | 2–4 | 1.2–0.6 | ||
|
4880 | 20 | 0.2 | ||
|
6220 | 25 | 0.2 | ||
|
2390 | 2 | 1.0 | ||
|
890 | 0.1 | 9.0 | ||
|
5550 | 15 | 0.4 | ||
|
2890 | 8 | 0.4 | ||
The greatest variation is thus to be expected in the distance from Greenland to Europe. The movement in this case is an east-west one, so that the astronomical position can only give an increase in the difference of longitude, not that of latitude.
The increase in the difference of longitude between Greenland and Europe has, as a matter of fact, already been noticed. J. P. Koch has compared, in the sixth volume of the results of the Danish Expedition,[3] page 240, in his section on the Survey of North-east Greenland in the chapter, 16 pages long, headed “The Drift of North Greenland in a Westerly Direction,” the longitude determinations of Sabine (1823), Börgen and Copeland (1870) and Koch (1907). He thereby obtained a difference which increased in the course of time, and which corresponds to an enlargement of the distance between North-east Greenland and Europe amounting to:—
- 420 m. or 9 m. per year in the period from 1823–1870.
- 1190 m. or 32 m. per„ year in„ the„ period„ from„ 1870–1907.
The determinations of longitude were not carried out on exactly the same spots. Sabine observed it on the southern margin of the island named after him. Unfortunately, there still exists in this matter some degree of uncertainty, to be sure not very important, about the exact spot, which would probably be removed by another examination of the locality. Börgen and Copeland made observations on the same area but some 100 metres to the east. Koch’s observations, on the other hand, were made much farther north on Danmarkshafen in Germania Land, but are connected by triangulation with Sabine Island. The inexactitudes arising from this carrying-over were exhaustively studied by Koch, with the result they can be disregarded when compared with the much greater inaccuracies of the longitude determinations themselves. Since these were obtained in all three cases by observations on the moon, the accuracy is of necessity much less than the determinations of longitude by means of wireless telegraphy. The mean error deduced from a comparison of the figures of each series of observations gives an idea of the degree of accuracy obtained. This mean error amounts to:—
in 1823 |
124 m. |
in„ 1870 |
124 m. |
in„ 1907 |
256 m. |
If we compare the mean errors with the observed alterations in longitude, we see that the latter are considerably greater. On that account Koch concluded[4] that: “It appears from the preceding that the sources of error given are neither singly nor collectively sufficient to suggest an explanation of the difference of about 1190 m. which exists between the position of Haystack, as determined by the Danmark-Ekspedition and the Germania-expedition. The only source of error, which in this connection plays any part, is the astronomical determination of longitude. But in order to explain the deviation through the error of the longitude of the observatory, we must put the actual error of the astronomical determination of longitude at four to five times the mean error, which is perfectly absurd.” F. Burmeister,[5] it is true, has objected to this on the grounds that the mean error only plays the part claimed for it, if there are an infinite number of observations, and that in this case the actual error of the result might reach the amount of the observed difference. Therefore he does not consider Koch’s proof as sufficient. Even if this is correct from the theoretical standpoint, and we cannot rely on the result obtained, but must attempt to obtain new and more accurate measurements by the aid of wireless telegraphy, I still believe that Burmeister’s criticism overshoots its mark. If the exact quantitative proof must be reserved for more accurate measurements, Koch would nevertheless have the prior claim to have made the first discovery of the alteration of co-ordinates.
As the table shows, a still greater amount of displacement is to be expected in the case of Cape Farewell. Also on Iceland the displacement in the course of five to ten years must be quite readily ascertainable.
The circumstances relating to the determination of the difference of longitudes of Europe-North America are less propitious. According to the table, an annual increase of distance of about 1 m. is to be expected, but this figure is an average one from the time of the break of Newfoundland from Ireland. But since then the direction of movement of North America seems to have been altered by the breaking away of Greenland, and now certainly appears to be directed more to the south. This is shown by the present relative positions of the corresponding points on the coasts of Labrador and South-west Greenland, and is confirmed by the direction of displacement (to be described in detail later) of the earthquake-fault of San Francisco, as well as the nascent compression of the Californian peninsula. It is therefore difficult to say how great the present-day increase of longitude might be. But in any case it must be less than 1 m. per annum. I at one time concluded, from the trans-Atlantic determinations of longitude obtained by the cable in 1866, 1870 and 1890, that there is an actual increase in distance of several metres a year. According to Galle,[6] however, the measurements based on this method cannot be accurately combined. Shortly before the war a new determination of longitude with regard to our problem was in operation, which was also controlled by a wireless measurement. Though this determination came to a premature end at the commencement of the war by the cutting of the cable, and consequently the result could not possess the desired accuracy, nevertheless it was evident that the alteration is still too small to be detected with any certainty. The difference of the longitude of Cambridge-Greenwich was, in fact, found to be[7]:—
in 1872 |
4 h. 44 m. 31.016 s. |
in„ 1892 |
4 h. 44 m. 31.032 s. |
in„ 1914 |
4 h. 44 m. 31.039 s. |
The oldest determination of 1866, for which I found 4 h. 44 m. 30.89 s., has been omitted, as it was alleged to be too inaccurate. It is certainly highly desirable that a new complete determination of longitude should be carried out, but the possibility must be reckoned with that the displacement is too small even then to be detectable with any degree of certainty.
But perhaps it will be possible to ascertain the displacement of North America by corresponding determinations of latitudes with Greenland. There certainly also exists the prospect, in the case of the difference of latitude of Madagascar and Africa, of measuring its alteration by repeated observations over not too lengthy a period.
Finally, reference should be made to the variation of the geographical latitudes of European and North American observatories. A. Hall[8] considered the following decrease of latitudes as proved:—Washington in 18 years about 0.47″; Paris in 28 years about 1.3″; Milan in 60 years about 1.51″; Rome in 56 years about 0.17″; Naples in 51 years about 1.21″; Königsberg (Prussia) in 23 years about 0.15″; Greenwich in 18 years about 0.51″. According to Kostinsky and Sokolow, Pulkowa observatory also showed a secular decrease of latitude. But since the discovery was made that systematic errors of similar dimensions arise through local refraction in the observatories, all deviations have been attributed to this source of error. Meanwhile those who believe that the international observations of latitude for Europe and America show a change of latitude are, of late, becoming more numerous, but it must be admitted that this change appears now to be in the nature of an increase of latitude.[9]
- ↑ Compare Dacqué, Grundl. u. Meth. d. Palägeographie, p. 273, Jena, 1915; and Rudzki, “L’Âge de la Terre,” Scientia, 13, No. 28, 2, pp. 161–173, 1915.
- ↑ J. Königsberger, “Berechnungen des Erdalters auf physikalischer Grundlage,” Geol. Rundsch., 1, p. 241, 1910.
- ↑ “Danmark-Ekspeditionen til Grönlands Nordöstkyst, 1906–1908,” under Ledelsen af L. Mylius-Erichsen, 6 (Meddelelser om Grönland, 46). Copenhagen, 1917.
- ↑ Op. cit., p. 242.
- ↑ F. Burmeister, “Die Verschiebung Grönlands nach dem astronomischen Längenbestimmungen,” Peterm. Mitt., pp. 225–237, 1921.
- ↑ Galle, “Entfernen sich Europa and Nordamerika von einander?” Deutsche Revue, Febr., 1916.
- ↑ Compare the Jahresber. d. preusz. Geodät. Instituts in Vierteljahrsschr. d. Astron. Ges., 51, p. 139, as well as the Astronomical Journal, No. 673/674.
- ↑ Günther, Lehrb. d. Geophysik., 1, p. 278. Stuttgart, 1897.
- ↑ W. D. Lambert, “The Latitude of Ukiah and the Motion of the Pole,” Journ. Wash. Acad. Sci., 12, No. 2, 1922.