THE CHAIN OF LIFE

Evening Post, Volume CXX, Issue 111, 6 November 1935, Page 28

THE CHAIN OF LIFE

OUR WORLD.AND FUTURE

SCIENTIST ON ITS RHYTHM

LUTES OF THE CONTINENTS

"Although infinitely richer than ° when Darwin wrote, the geological record," said Professor W. W. a Watts, president of the British h Association, in his address to, the Norwich meeting i>£ that body (reports y "The Times"), ' still is, and must from its very nature remain, imperfect, t] Every major group of animal life but F the vertebrates is represented in the *, Cambrian faun;;, and the scant relics v that have been recovered from earlier i) rocks give veiy little idea of what o had gone before, and no evidence d whatever as to the beginnings of life, t: But, from Cambrian time onwards the tl chain of life i;:: continuous and un- ii broken. Type ;ifter type has arisen, p flourished, and attained dominion, tl Some of them have met extinction in o the heyday o:! their development; c others have slowly dwindled away; others, again, have not finished their n downhill journey, or are still advanc- £ ing to their climax. r "Study of ths succession of rocks ti and the organisns contained in them, ii in every case in which evidence is ti sufficiently abundant and particularly v among the vertebrates and in the later ti stages of geological history, has now 1« revealed that the great majority of v species show close affinities with those h which preceded and with those which y followed them; that, indeed, they c have been derived from their predecessors and gave origin to their sue- , cessors. We may now fairly claim that jj palaeontology has lifted the theory t , of evolution of organisms from the j limbo of hypothesis into a fact com- g ! pletely demonstrated by the integral chain of life which links the animals t] and plants of today with the earliest of their forerunners of the most c remote past. ;] "Further, the rocks themselves yield r proof of the geographical changes t . undergone by the earth during its „ physical history; and indicate with a perfect clearness that these changes j have been so closely attendant on a variation in life, and the incoming of 0 new species, that it is impossible to v deny a relation of cause and effect. c Indeed, when we realise the delicate t ; adjustment of all life to the four 0 elements of the ancients which environ it, air, water, earth, and fire; to their g composition, interrelationships, and circulation; it is, perhaps, one of the _ most remarkable facts established by v geology that, in spite of the physical j, changes which we know to have occurred, the chain of life has never c snapped in all the hundreds of. mil- 0 lions of years through which its history has been traced." WORK OF STJESS. c The physical changes with which * Lyell and his successors were most ' closely concerned, the president con- ; tinued, were firstly the formation of * stratified rocks on horizontal sea-floors, * situated in what was now often the " interior of continents, far removed s from the oceans of the present day, c and thus indicating important and repeated changes in the position of ji land and water; and, secondly, the ( deformation of these flat deposits till r they were rucked and ridged to build J; the mountain ranges. It was not till £ 1885, however, that the accumulation *■ of data of this type was sufficient to r enable the great geologist, Eduard c Suess, an Austrian, but born in this \ country, to assemble and correlate s them, and to deduce from them fur- * ther principles which had been the ' mainstay and inspiration of his sue- ' cessors. The evidence collected by Suess proved that great land and sea changes t had occurred simultaneously over i whole continents or even wider regions. Such great submergences as t those to which ths Cambrian Rocks, 1 the Oxford Clay, and the Chalk were t due were of this character; while, in c between, there came times of broad c expansions of continental land and re- c gressions of the sea. These changes i were in his view on far too grand a c scale to be compared with, or ex- c plained by, the trivial upheavals and s depressions of land margins of the 1 present day, which he showed could 1 mostly be correlated with volcanoes or i earthquakes, or with such incidents c as the imposition or relief of ice-sheets ; on an elastic crust in connection with glacial conditions. 1 OTHEE INVESTIGATORS. \ It was when Lord Kelvin's dictum . struck from geology its grandest con- ] ception, time, that it became vital to , re-examine the position. He had , demonstrated that if the earth had , been continually cooling down at its ; present rate its surface must have , been too hot for the existence of life upon it a limited number of million ' years ago. To a host of competent ■ and devoted observers, all over, the , world, familiar with the tremendous , changes, organic and inorganic, that the earth had passed through since Cambrian time, it was wholly impos- , sible to compress the life story of the earth, or the history of life upon it, into a paltry 20 or 30 million years. It was only fitting that the great physicist who imposed a narrow limit to geological time should have prepared the way for those who had proved that the earth possesses in its radioactive substances a "hidden reserve" capable of supplying a continuous recrudescence of the energy wasted by radiation, thus lengthening out the time required to complete its total loss. The far-sighted genius of Lord Rutherford and Lord Rayleigh first saw the bearing of the rate of disintegration of radioactive substances in the minerals of rocks on the age of the parts of the earth-crust built of them. The extension and supplementing of this work by Joly, Holmes, and others had now enabled them to look to the disintegration of uranium, thorium, and potassium as the most promising of many methods that had been used in the endeavour to ascertain the age of those parts of the earth-crust that were accessible to observation. These methods also provided a means of dating the geological succession of eras and periods in terms of millions if not hundreds of thousands of years. The decline and early death to which Lord Kelvin's dictum had condemned the earth, according so little with the vigour displayed in its geological story, was now transformed into a history of prolonged, though not perennial, youth. It was for Joly, of whose work the extent, variety, and fruitfulness were hardly yet fully appreciated, to take the next step and see in the release of radioactive energy a mechanism which could drive the pulse that geologists had so long felt, and that Suess had so brilliantly diagnosed. As Darwin found the missing word for Lyell, so Joly in his theory of Thermal Cycles had indicated the direction of search. THE EARTH'S ENERGY. "In Joly's conception," the president continued, "the running down of the earth's energy, though a continuous process, was, through the intervention of radioactivity, converted into a series of cycles, during each of which relative movements of sea and land must occur; downward movements of the continents, associated with posi-

tive encroachments of the sea; upward w movements, with retreat of the sea, the h formation of wide land masses, and d the ridging of strata to form mountain tl ranges. Thus he forged a link that n could unite the continental or epeiro- tl genie movement with orogenic or n mountain movement. n "The visible parts of mountains and v, continents, as well as their -lower and o hidden portions, or • 'roots,' are made a of comparatively light rocks. In order i( to stand up as they do their roots X must be embedded in denser matter, n in . which they 'float' like icebergs in water. A far larger mass must exist tl below than is visible above, and the ii bigger the upstanding part the bigger c the submerged root. Over the larger tl area of the ocean floor, on the other n hand, the thickness of material of d low density must be very slight, and o the denser layer must come closer to d the surface. a "The study of earthquakes, to which ti the Seismology Committee of the o British Association has made outstand- ii ing contributions, has yielded, from b the times taken in transmissions of ti vibrations through the earth, the best b information as to the nature and state n of the interior. It has proved that the v dense layer is solid at the present v time. It is probably no coincidence a that the earth is also but just recover- n ing from what is possibly the greatest r period of mountain-building, if not r the greatest negative movement of ocean retreat, that it has ever n experienced. , d "But solidity cannot be the per- d manent condition of the substratum, ii Heat is generated in it by its own a radioactivity, but, according to the I terms of the hypothesis, cannot escape, 1: in consequence of the higher tempera- T ture generated in the continental rocks d which cover it. It is, therefore, re- n tamed in the substratum and stored as h latent heat of liquefaction, so that, a within a period which has been calcu- s lated approximately in millions of o years, complete melting of the sub- s crust must ensue. s ENCROACHING WATERS. r - "The resulting expansion of the c liquefied stratum will have at least £ two effects of great importance to us. i* In the first place the unexpanded superficial layers will be too small to c fit the swelling interior. They will, therefore, suffer tension, greater on F the ocean floor than on land, and ) cracking and rifting will occur, with . intrusion and extrusion of molten v rock. In the second place the con- r tinental masses, now truly floating in J a substratum which has become fluid and less dense than before, will sink J deeper into it, suffering displacement along the rift cracks or other planes of dislocation. As a result the ocean r waters, unchanged in volume, must a encroach on the edges of the con- s tinents and spread further and further over their surfaces. "Thus we have the mechanism which Suess vainly sought, causing positive movements of the oceans, their waters spreading over wide stretches of what 1 was formerly continental land, and I laying down as sediment upon it the V marine stratified rooks which are our 1 chief witness of the rhythmic advances j of the sea. I "The view at which we have ar- s rived," Professor Watts said, after dis- ] cussing the work of Professor Arthur 2 Holmes in checking Joly's calcula- * tions, "is neither strictly uniformi- 3 tarian nor -strictly catastrophic, but c takes the best from each hypothesis. As Lyell showed, most of the phe- * nomena of geology can be matched £ somewhere and sometime on the * earth of today." * The contrast in outline and structure 1 between the Atlantic and Pacific 2 Oceans, he continued, had long been noted when Suess .formulated and c used the differences as the basis of ' his classification. The Pacific was ' bounded everywhere by steep slopes, ' rising abruptly from profound ocean * depths to lofty lands crowned with . mountain ranges, parallel to its shores and surrounding its whole area. The Atlantic, on the other hand, was not bordered with continuous ranges, but broke across them all. THE WEGENER THEORY. Another feature of the Atlantic was the parallelism of much of its eastern and western coasts, the meaning of which had often attracted the speculations of geologists and geographers. With a little stretch of the imagination, and some ingenuity and elasticity of adjustment, plans or maps of the opposite sides might be fitted fairly closely, particularly if they plotted and assembled the real edges of the continents, the steep slopes which divided the "shelves" on which they . stood from- the ocean depths. This ! had suggested the possibility that the . two sides might once have been 1 united, and had since broken and i drifted apart till they were now separ- : ated by the ocean. , i This view, outlined by others, had been emphasised by Wegener and dealt with by him in full detail in his work on "The Origin of Continents 1 and Oceans," and it now played a leading par^: in what was known as J the Wegener theory of continental drift. "The hypothesis," the president 1 observed, "is supported by the close ' resemblances in the rocks and fossils ;of many ages in Western Europe and ; Britain to those of Eastern North 1 America; by community of the structures by which these rocks are affect- ■ ed; and by '.he strong likeness exhibit- ' ed by the living animals and plants on ' the two sides, so that they can only ; be referred' to a single biological and " distribution.] 1 unit, the Palaearctic ; Region. * "The hypothesis, however, did not ' stop at this; and in the South Atlantic ' and certain other areas Wegener and " his followers have also given good 3 reasons for believing that continental 5 masses, once continuous, have drifted " apart. Broad areas in Southern Africa * are built of rocks known as the Karroo 2 Formation, of which the lower part, of 3 late Carboniferous age, is characterD ised especially by species of the strange fern-like fossil plants Glossopteris and * Gangamopteris. Associated with them ' are peculiar groups of fossil shells and " fossil amphibia and reptiles. Similar 1 rocks, with similar associations and f contents, in Peninsular India have £ been named the Gondwana Formation. ■' Comparable Formations also occupy * large regions in Australia, Tasmania, 1 and New Zealand, in Madagascar, in '• the Falkland Islands and Brazil, and t in Antarctica. J GOND WAN ALAND. c "The correspondence between these ~ areas is so close that Suess supposed [. they must at that date have been conl nected together by lands, now sunk s beneath the sea, and he named the f continent thus formed Gondwanaland after the Indian occurrences. The d break-up of this land can be followed d from a study of the rocks, and it was c a slow process, its steps occupying r t much of Mesozoic time. Dr. A. L. dv ,f Toifs comparison of South African 1_ rocks with those of Brazil and else1^ where in South America favours even 1S a closer union than this between the 0 units now scattered. >. "One of the most remarkable feaj. tures shown by these rocks in all the ,t areas mentioned, but to varying exL t tents, is the presence of conglomerates j made of far-travelled boulders, ,j scratched like those ' borne by the t l modern ice-sheets of Greenland and ,f the Antarctic, associated with other deposits of a glacial nature, and often resting upon typical glaciated surfaces. There is no possible escape from the it conclusion that these areas, now c situated in or near the Tropics, suffered j is an intense glaciation. n "This was not a case of mere alpine a glaciers, for the land was of low relief h and not far removed from sea-level, d but of extensive ice-sheets on a far if I larger scale than the glaciation of the i-1 northern parts of the new and old

worlds in the Pleistocene ice Age. I have never seen any geological evidence more impressive or convincing than that displayed at Nooitgedacht, near Kimberley. Dv Toit's work on these glacial deposits brings out two remarkable facts; first, that the movement of the ice was southerly, poleward and away from the Equator, the opposite to what .would be expected, and to the direction of the Pleistocene ice-movement; secondly, that the ice in Natal invaded the land from what is now sea to- the north-east. When it is realised that at this period there is no evidence of glacial action in northern Europe or America, but a climate in which grew the vegetation that formed the coal seams of our coal measures, it is clear that we are not dealing with any general refrigeration of the globe, even if that would produce such widespread glaciation: we are face to face with a special glaciation of Gondwanaland. On both sides of the Atlantic these glacial episodes in Carboniferous times were followed by dry and desert climates in Triassic time, and these by violent volcanic outbursts. Nor are the rocks alike only in mode of formation, the structures by which they are traversed correspond; while even in details there is remarkable agreement, as in the peculiar manganese deposits, and the occurrence of diamonds in "pipes" of igneous rock, both east and west of the Ocean. If a hypothesis of drift were admitted for Gondwanaland, the president submitted, it would be illogical to deny its application to other regions including the North Atlantic, and he added the comment: "Can the Pilgrim Fathers have ever dreamed of such a link between the Old England and the New?" The hypothesis of continental drift gave rich promise of solving so many difficult problems that it was hailed by many classes of investigators almost as a panacea. Geographers had seen in it an explanation of the forms of continents and the position of peninsulas, islands, and mountains; geodesists had welcomed escape from the rising and sinking of the crust, so difficult to reconcile with the de-; mands of isostatic equilibrium; and it I had been already stated that drift formed a vital factor in Joly's thermal cycles. It had been assailed, however, on the one hand, for the detail attempted in its geographical restorations, and, on the other, for its vagueness. If the idea of drift were accepted, it could not be regarded as a royal road out of all difficulties, nor could it be the only form of earth movement to be re'ekoned with. The facts of life distribution were far too complex to be explained by any single period of connection followed by a definite breaking apart, even if that took place by stages.