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.L.du Toit, a South African scientist, offered a variation ofWegener's theory, namely, a "concept of an earth in which the periodic, though variable,softening of the sub-crust through radioactive heating enables the skin to creep differentiallyover the core with consequent wrinkling." 4As for the mountains, not all of them are situated as long ridges parallel to the seacoast.And nocompelling evidence has been brought to support the contention that ice ages were consecutivein various parts of the Southern Hemisphere and, in much more recent times, in various parts ofthe Northern Hemisphere.Furthermore, how explain signs of the recent Ice Age in the SouthernHemisphere? In Patagonia, New Zealand, and other places in the Southern Hemisphere, signsof recent glaciation are found.It is also certain that the chilling of the Ice Age was simultaneousall over the world.8 H.Jeffreys, The Earth, Its Origin, History and Physical Constitution (2nd ed.; 1929), p.304.4 A.L.du Toit, Our Wandering Continents (1937), p.3. Coal is found not only in arctic lands but also in Ant-arctics.Old, then, this continent travel there from the tropics? And what was the motive force?If the theory is correct, the motion of the continents should be observable at present; yet, thoughWegener claimed, on the basis of certain reports, that Greenland and an island near its westerncoast still move, repeated observations and triangulations do not support this claim.Wegenerperished on an expedition to Greenland in 1930.The assumption that ocean floors and continents are eternally different in structure is incontradiction to a great number of observations, though the land surface has been betterexplored than the bottom of the sea.The idea of a basic difference between the rocks of theocean bottom and those of the continents is disproved wherever the fossiliferous contents of theland and of the ocean bed are examined.Marine expeditions have failed to find at various placeson the ocean bottom the thick layers of sediment that should have been present if the sea hadbeen covering the areas for untold centuries.On the other hand, sediments thousands and eventens of thousands of feet thick have been found on continents.Not only were large stretches ofland in North America and Europe and Asia covered by the sea at various tunes in the pastand some well-investigated localities, like the gypsum beds of Pans, show repeated returns ofthe waters but even the largest and highest mountain chains the Alps, the Andes, theHimalayas at some time were under the sea.Since the ocean once covered a vast expanse ofland, it may at present occupy the place of former land.The land masses of today do not change their latitudes; the motive force claimed is insufficientby far.Coal beds in Antarctica and recent glaciation in temperate latitudes of the SouthernHemisphere all conspire to invalidate the theory of wandering continents.The Changing OrbitThe theory of sliding continents having been shown to be built on infirm foundations, thereremain three theoretical changes in the position of the terrestrial globe or its shell in relation tothe sun that could cause great variations of climate: a change in the form of the orbit, or the paththe earth follows around the sun; a change in the astronomical direction of the axis; a change inthe position of the terrestrial shell in relation to the core, and thus in the position of the poles(sliding shell).At present the elliptical form of the orbit changes by a very small amount.This could be theresidue of a displacement the earth suffered on its path; but following the principle of Laplaceand Lagrange concerning the stability of the planetary system, this variation in the shape of theterrestrial orbit is considered to be an oscillation, the mean shape of the orbit being regarded asfixed.The period of this oscillation is supposed to be of very long duration.The obliquity of the ecliptic, or the angle which the plane of the equator makes with the plane ofthe earth's orbit, is 23 °; this obliquity causes the sequence of the seasons.It changes now atthe rate of 0.47' a year, "but the limits of its variation are difficult to calculate." * The figuresoffered by various mathematicians differ greatly.Lagrange estimated the angle of the swing tobe as large as 7° with a period that had its last maximum in the year 2167 before the present era;Stockwell calculated the angle of oscillation at less than 3 °; while Drayson estimated that theobliquity ranged from 35° to 11°, that is, a swing of 24.2 This variation, whatever its numericalvalue, could have been caused by a disturbance which the earth suffered; but again, the causebeing unidentified, the effect is considered to be a permanent oscillation.1 Brooks, Climate through the Ages (2nd ed.; 1949), p.102.2 ibid.The earth experiences the precession of the equinoxes, or a large spin of the axis withconsequent displacement of the seasons in relation to the perihelion (the point on the orbitclosest to the sun).This precession or "preceding" of the vernal and autumnal equinoxes is as great as 50.2' in a year, and the terrestrial axis describes a wide circle in the sky in a periodestimated at about 26,000 years.Newton explained this phenomenon, known since the days ofHipparchus ( 120), as produced by the attractive effect of the sun and the moon on the bulgingpart of the equator.But this explanation does not account for what in the first place caused theearth's bulging part or equator to take the position under an angle to the plane of terrestrialrevolution, or ecliptic.This swing of the terrestrial axis as though the globe were a top disturbed in its motion couldalso be caused by a disturbance in the motion of the earth experienced sometime in the past.Finally, we have already spoken of the wobbling of the terrestrial axis, or its describing a smallcircle around the geographical pole, or, better, of the wandering of the pole that causes smallvariations in latitudes, discovered late in the nineteenth century.A theory that employed the changes in eccentricity of the orbit and the precession of theequinoxes to explain the variations of climate was advanced in 1864 by James Croll, andaccepted by Charles Darwin and others; it has since been abandoned, for it requires alternateglacial ages in the Northern and Southern hemispheres, and the evidence contradicts such anorder of events.More recently, M.Milankovitch introduced the third variable, the obliquity of the ecliptic, tocorrect some of the defects of Croll's theory.In the opinion of his critics, however, his curve ofclimatic changes widely upsets geological dates; nor do his variables offer sufficiently effectivereasons for the vigorous changes of climate.Besides, he assigned an arbitrary length to theoscillation period of obliquity [ Pobierz caÅ‚ość w formacie PDF ]
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.L.du Toit, a South African scientist, offered a variation ofWegener's theory, namely, a "concept of an earth in which the periodic, though variable,softening of the sub-crust through radioactive heating enables the skin to creep differentiallyover the core with consequent wrinkling." 4As for the mountains, not all of them are situated as long ridges parallel to the seacoast.And nocompelling evidence has been brought to support the contention that ice ages were consecutivein various parts of the Southern Hemisphere and, in much more recent times, in various parts ofthe Northern Hemisphere.Furthermore, how explain signs of the recent Ice Age in the SouthernHemisphere? In Patagonia, New Zealand, and other places in the Southern Hemisphere, signsof recent glaciation are found.It is also certain that the chilling of the Ice Age was simultaneousall over the world.8 H.Jeffreys, The Earth, Its Origin, History and Physical Constitution (2nd ed.; 1929), p.304.4 A.L.du Toit, Our Wandering Continents (1937), p.3. Coal is found not only in arctic lands but also in Ant-arctics.Old, then, this continent travel there from the tropics? And what was the motive force?If the theory is correct, the motion of the continents should be observable at present; yet, thoughWegener claimed, on the basis of certain reports, that Greenland and an island near its westerncoast still move, repeated observations and triangulations do not support this claim.Wegenerperished on an expedition to Greenland in 1930.The assumption that ocean floors and continents are eternally different in structure is incontradiction to a great number of observations, though the land surface has been betterexplored than the bottom of the sea.The idea of a basic difference between the rocks of theocean bottom and those of the continents is disproved wherever the fossiliferous contents of theland and of the ocean bed are examined.Marine expeditions have failed to find at various placeson the ocean bottom the thick layers of sediment that should have been present if the sea hadbeen covering the areas for untold centuries.On the other hand, sediments thousands and eventens of thousands of feet thick have been found on continents.Not only were large stretches ofland in North America and Europe and Asia covered by the sea at various tunes in the pastand some well-investigated localities, like the gypsum beds of Pans, show repeated returns ofthe waters but even the largest and highest mountain chains the Alps, the Andes, theHimalayas at some time were under the sea.Since the ocean once covered a vast expanse ofland, it may at present occupy the place of former land.The land masses of today do not change their latitudes; the motive force claimed is insufficientby far.Coal beds in Antarctica and recent glaciation in temperate latitudes of the SouthernHemisphere all conspire to invalidate the theory of wandering continents.The Changing OrbitThe theory of sliding continents having been shown to be built on infirm foundations, thereremain three theoretical changes in the position of the terrestrial globe or its shell in relation tothe sun that could cause great variations of climate: a change in the form of the orbit, or the paththe earth follows around the sun; a change in the astronomical direction of the axis; a change inthe position of the terrestrial shell in relation to the core, and thus in the position of the poles(sliding shell).At present the elliptical form of the orbit changes by a very small amount.This could be theresidue of a displacement the earth suffered on its path; but following the principle of Laplaceand Lagrange concerning the stability of the planetary system, this variation in the shape of theterrestrial orbit is considered to be an oscillation, the mean shape of the orbit being regarded asfixed.The period of this oscillation is supposed to be of very long duration.The obliquity of the ecliptic, or the angle which the plane of the equator makes with the plane ofthe earth's orbit, is 23 °; this obliquity causes the sequence of the seasons.It changes now atthe rate of 0.47' a year, "but the limits of its variation are difficult to calculate." * The figuresoffered by various mathematicians differ greatly.Lagrange estimated the angle of the swing tobe as large as 7° with a period that had its last maximum in the year 2167 before the present era;Stockwell calculated the angle of oscillation at less than 3 °; while Drayson estimated that theobliquity ranged from 35° to 11°, that is, a swing of 24.2 This variation, whatever its numericalvalue, could have been caused by a disturbance which the earth suffered; but again, the causebeing unidentified, the effect is considered to be a permanent oscillation.1 Brooks, Climate through the Ages (2nd ed.; 1949), p.102.2 ibid.The earth experiences the precession of the equinoxes, or a large spin of the axis withconsequent displacement of the seasons in relation to the perihelion (the point on the orbitclosest to the sun).This precession or "preceding" of the vernal and autumnal equinoxes is as great as 50.2' in a year, and the terrestrial axis describes a wide circle in the sky in a periodestimated at about 26,000 years.Newton explained this phenomenon, known since the days ofHipparchus ( 120), as produced by the attractive effect of the sun and the moon on the bulgingpart of the equator.But this explanation does not account for what in the first place caused theearth's bulging part or equator to take the position under an angle to the plane of terrestrialrevolution, or ecliptic.This swing of the terrestrial axis as though the globe were a top disturbed in its motion couldalso be caused by a disturbance in the motion of the earth experienced sometime in the past.Finally, we have already spoken of the wobbling of the terrestrial axis, or its describing a smallcircle around the geographical pole, or, better, of the wandering of the pole that causes smallvariations in latitudes, discovered late in the nineteenth century.A theory that employed the changes in eccentricity of the orbit and the precession of theequinoxes to explain the variations of climate was advanced in 1864 by James Croll, andaccepted by Charles Darwin and others; it has since been abandoned, for it requires alternateglacial ages in the Northern and Southern hemispheres, and the evidence contradicts such anorder of events.More recently, M.Milankovitch introduced the third variable, the obliquity of the ecliptic, tocorrect some of the defects of Croll's theory.In the opinion of his critics, however, his curve ofclimatic changes widely upsets geological dates; nor do his variables offer sufficiently effectivereasons for the vigorous changes of climate.Besides, he assigned an arbitrary length to theoscillation period of obliquity [ Pobierz caÅ‚ość w formacie PDF ]