One of the most fascinating fields for speculation is the age of the submarine mountains compared with that of past and present mountains of the continents. Looking back over the past ages of geologic time (see chart in The Gray Beginnings), we realize that mountains have been thrust up on the continents, to the accompaniment of volcanic outpourings and violent tremblings of the earth, only to crumble and wear away under the attacks of rain and frost and flood. What of the sea’s mountains? Were they formed in the same way and do they, too, begin to die as soon as they are born?
There are indications that the earth’s crust is no more stable under sea than on land. Quite a fair proportion of the world’s earthquakes are traced through seismographs to sources under the oceans, and, as we shall see later, there are probably as many active volcanoes under water as on land. Apparently the Atlantic Ridge arose along a line of crustal shifting and rearrangement; although its volcanic fires seem to be largely quiescent, it is at present the site of most of the earthquakes in the Atlantic area. Almost the whole continental rim of the Pacific basin is aquiver with earthquakes and fiery with volcanoes, some frequently active, some extinct, some merely sleeping a centuries-long sleep between periods of explosive violence. From the high mountains that form an almost continuous border around the shores of the Pacific, the contours of the land slope abruptly down to very deep water. The deep trenches that lie off the coast of South America, from Alaska along the Aleutian Islands and across to Japan, and southward off Japan and the Philippines give the impression of a landscape in process of formation, of a zone of earth subject to great strains.
Yet the submarine mountains are earth’s nearest approach to the ‘eternal hills’ of the poets. No sooner is a continental mountain thrust up than all the forces of nature conspire to level it. A mountain of the deep sea, in the years of its maturity, is beyond the reach of the ordinary erosive forces. It grows up on the ocean floor and may thrust volcanic peaks above the surface of the sea. These islands are attacked by the rains, and in time the young mountain is brought down within reach of the waves; in the tumult of the sea’s attack it sinks again beneath the surface. Eventually the peak is worn down below the push and pull and drag of even the heaviest of storm waves. Here, in the twilight of the sea, in the calm of deep water, the mountain is secure from further attack. Here it is likely to remain almost unchanged, perhaps throughout the life of the earth.
Because of this virtual immortality, the oldest oceanic mountains must be infinitely older than any of the ranges left on land. Professor Hess, who discovered the sea mounts of the central Pacific, suggested that these ‘drowned ancient islands’ may have been formed before the Cambrian period, or somewhere between 500 million and 1 billion years ago. This would make them perhaps of an age with the continental mountains of the Laurentian upheaval. But the sea mounts have changed little if at all, comparing in elevation with modern terrestrial peaks like the Jungfrau, Mt. Etna, or Mt. Hood; while of the mountains of the Laurentian period scarcely a trace remains. The Pacific sea mounts, according to this theory, must have been of substantial age when the Appalachians were thrust up, 200 million years ago; they stood almost unchanged while the Appalachians wore down to mere wrinkles on the earth’s face. The sea mounts were old, 60 million years ago, when the Alps and the Himalayas, the Rockies and the Andes, rose to their majestic heights. Yet it is probable that they will be standing unchanged in the deep sea when these, too, shall have crumbled away to dust.
As the hidden lands beneath the sea become better known, there recurs again and again the query: can the submerged masses of the undersea mountains be linked with the famed ‘lost continents’? Shadowy and insubstantial as are the accounts of all such legendary lands—the fabled Lemuria of the Indian Ocean, St. Brendan’s Island, the lost Atlantis—they persistently recur like some deeply rooted racial memory in the folklore of many parts of the world.
Best known is Atlantis, which according to Plato’s account was a large island or continent beyond the Pillars of Hercules. Atlantis was the home of a warlike people ruled by powerful kings who made frequent attacks upon the mainlands of Africa and Europe, brought much of Libya under their power, roamed the Mediterranean coast of Europe, and finally attacked Athens. However, ‘with great earthquakes and inundations, in a single day and one fatal night, all who had been warriors [against Greece] were swallowed up. The Island of Atlantis disappeared beneath the sea. Since that time the sea in these quarters has become unnavigable; vessels cannot pass there because of the sands which extend over the site of the buried isle.’
The Atlantis legend has lived on through the centuries. As men became bold enough to sail out on the Atlantic, to cross it, and later to investigate its depths, they speculated about the location of the lost land. Various Atlantic islands have been said to be the remains of a land mass once more extensive. The lonely wave-washed Rocks of St. Paul, perhaps more often than any other, have been identified as the remains of Atlantis. During the past century, as the extent of the Atlantic Ridge became better known, speculations were often centered upon this great mass, far below the surface of the ocean.
Unfortunately for these picturesque imaginings, if the Ridge was ever exposed, it must have been at a time long before there were men to populate such an Atlantis. Some of the cores taken from the Ridge show a continuous series of sediments typical of open oceans, far from land, running back to a period some 60 million years ago. And man, even the most primitive type, has appeared only within the past million years or so.
Like other legends deeply rooted in folklore, the Atlantis story may have in it an element of truth. In the shadowy beginnings of human life on earth, primitive men here and there must have had knowledge of the sinking of an island or a peninsula, perhaps not with the dramatic suddenness attributed to Atlantis, but well within the time one man could observe. The witnesses of such a happening would have described it to their neighbors and children, and so the legend of a sinking continent might have been born.
Such a lost land lies today beneath the waters of the North Sea. Only a few scores of thousands of years ago, the Dogger Bank was dry land, but now the fishermen drag their nets over this famed fishing ground, catching cod and hake and flounders among its drowned tree trunks.
During the Pleistocene, when immense quantities of water were withdrawn from the ocean and locked up in the glaciers, the floor of the North Sea emerged and for a time became land. It was a low, wet land, covered with peat bogs; then little by little the forests from the neighboring high lands must have moved in, for there were willows and birches growing among the mosses and ferns. Animals moved down from the mainland and became established on this land recently won from the sea. There were bears and wolves and hyenas, the wild ox, the bison, the woolly rhinoceros, and the mammoth. Primitive men moved through the forests, carrying crude stone instruments; they stalked deer and other game and with their flints grubbed up the roots of the damp forest.
Then as the glaciers began to retreat and floods from the melting ice poured into the sea and raised its level, this land became an island. Probably the men escaped to the mainland before the intervening channel had become too wide, leaving their stone implements behind. But most of the animals remained, perforce, and little by little their island shrank, and food became more and more scarce, but there was no escape. Finally the sea covered the island, claiming the land and all its life.
As for the men who escaped, perhaps in their primitive way they communicated this story to other men, who passed it down to others through the ages, until it became fixed in the memory of the race.
None of these facts were part of recorded history until, a generation ago, European fishermen moved out into the middle of the North Sea and began to trawl on the Dogger. They soon made out the contours of an irregular plateau nearly as large as Denmark, lying about 60 feet under water, but sloping off abruptly at its edges into much deeper water. Their trawls immediately began to bring up a great many things not found on any
ordinary fishing bank. There were loose masses of peat, which the fishermen christened ‘moorlog.’ There were many bones, and, although the fishermen could not identify them, they seemed to belong to large land mammals. All of these objects damaged the nets and hindered fishing, so whenever possible the fishermen dragged them off the bank and sent them tumbling into deep water. But they brought back some of the bones, some of the moorlog and fragments of trees, and the crude stone implements; these specimens were turned over to scientists to identify. In this strange debris of the fishing nets the scientists recognized a whole Pleistocene fauna and flora, and the artifacts of Stone Age man. And remembering how once the North Sea had been dry land, they reconstructed the story of Dogger Bank, the lost island.
* The range of echo-sounding instruments has now been so greatly extended that under ideal conditions the most powerful of them are capable of sounding the maximum depths of the sea. Factors such as the nature of the underlying bottom and conditions in the intervening water layers influence the effectiveness with which the sounding devices operate under actual conditions at sea. Nevertheless, the potential range necessary for charting all parts of the sea is now at the command of oceanographers.
* In the ten years that have elapsed since this account of the canyons was written much more has been learned about them, but it may still be said that there is no general agreement about their origin. Many of the resources of the modern oceanographer have been brought to bear on the problem. Divers have engaged in direct exploration of the shallow heads of some of the California canyons, collecting samples of their walls and photographing them. Other canyons have been studied by oceanographers using deep-sea corers or dredges to obtain samples of rocks and sediments. Precision depth recorders have given much new information about their shapes. As a result of these studies it is now known that there are at least five types of canyons, so different in their characteristics that almost certainly they have different origins. No single theory may be expected to explain all of them. Professor Francis S. Shepard, the marine geologist who originally put forward the theory that the canyons had been cut by rivers and later submerged, now feels this explanation is adequate for some canyons but not for others. For example, some marine valleys, trough-shaped and straight-walled and occurring in areas where the earth’s crust is in a state of unrest, probably represent a fault or fracture of the rocky floor. The theory that some of the canyons have been cut by vast sediment flows called turbidity currents has gained support as a result of new concepts of dynamic activity on the floor of the sea. Further detailed study of all types of these extraordinarily fascinating features of the sea floor should not only clarify their own history but add greatly to our understanding of the history of the earth.
*Somewhat greater depths have more recently been recorded in the Mariana Trench off the island of Guam, the trench into which the bathyscaphe Trieste made its record-breaking descent to the bottom. In this trench the Challenger in 1951 recorded a depth of 10,863 meters or about 6.7 miles. Since the exact location of the Challenger echo sounding was given, this depth is capable of verification and so is regarded as the maximum depth of which we have authentic record. In 1958, however, Russian scientists aboard the Vitiaz reported a finding of slightly greater depths (11,034 meters or 6.8 miles) also in the Mariana Trench, but at an unspecified location.
*From The Changing World of the Ice Age, 1934 edition, Yale University Press, p. 116.
*The supposition that the Atlantic Ridge may extend across the Arctic basin has been confirmed in exciting new developments in marine geology. Indeed, it is now suggested by some geologists that the whole mid-Atlantic ridge is part of a continuous range of mountains that runs for 40,000 miles across the bottom of the Atlantic, the Arctic, the Pacific, and the Indian Oceans (see Preface).
As for the exploration of the Arctic basin itself—the charting of details so long unknown and merely guessed at—the revolutionary development that made it possible to substitute fact for theory was the use of American nuclear-powered submarines to pass beneath the ice cover and directly explore the depths of this ocean. In 1957 the Nautilus (bearing the same name as Wilkin’s conventional submarine) first penetrated beneath Arctic ice in a preliminary exploration designed to discover whether it was feasible to explore these regions by submarines. The Nautilus remained submerged for 74 hours and covered a distance of almost 1000 miles. A vast amount of data was collected, including depth soundings and measurements of the thickness of the overlying ice. Then in 1958 the Nautilus crossed the entire Arctic basin from Point Barrow in Alaska to the North Pole and thence to the Atlantic. In the course of this historic voyage it made the first continuously recorded echo-sounder profile across the center of the Arctic basin. Other nuclear submarines have subsequently contributed to our knowledge of the Arctic. It is now clear, from the work of the nuclear submarines and from other, more conventional explorations, that the bottom topography of the Arctic Ocean is for the most part that of a normal oceanic basin, with flat abyssal plains, scattered sea mounts, and rugged mountains. The greatest depth so far discovered is somewhat more than three miles. The shelf break (from which a steeper descent begins) falls at the unusually shallow depth of 35 fathoms off Alaska. From samplings by coring tubes and dredges and from deep-sea photography it was discovered during the International Geophysical Year that the bottom is widely covered with rocks, pebbles, and shells, the latter chiefly of shallow-water forms. The present ice cover seems to be carrying little or no material such as rock fragments and sand, so the material now found in bottom samples must have come from ice rafted in from surrounding continents during some past geologic time, when the Arctic was relatively open water.
Russian scientists, who have done rather extensive work in marine biology, obtained interesting data which seem to disprove Nansen’s earlier belief that the waters of the central Arctic are extremely poor in both plant and animal life. Data collected from the drifting station “North Pole” indicate that both plant and animal plankton in great variety exist in the region of the Pole. Little-studied organisms develop on the surface of the ice; these contain much fat and tint the ice shades of yellow and red. Diatoms are not found in the surface of the ice but develop (along with other plankton) in the lakes that form on the surface of the ice as it melts. By absorbing a great amount of energy from the sun, the abundant diatom colonies contribute to further melting of the ice cover. The wealth of plankton during the Arctic summer attracts numbers of birds and various mammals.
The Long Snowfall
A deep and tremulous Earth-Poetry.
LLEWELYN POWYS
EVERY PART OF EARTH or air or sea has an atmosphere peculiarly its own, a quality or characteristic that sets it apart from all others. When I think of the floor of the deep sea, the single, overwhelming fact that possesses my imagination is the accumulation of sediments. I see always the steady, unremitting, downward drift of materials from above, flake upon flake, layer upon layer—a drift that has continued for hundreds of millions of years, that will go on as long as there are seas and continents.
For the sediments are the materials of the most stupendous ‘snowfall’ the earth has ever seen. It began when the first rains fell on the barren rocks and set in motion the forces of erosion. It was accelerated when living creatures developed in the surface waters and the discarded little shells of lime or silica that had encased them in life began to drift downward to the bottom. Silently, endlessly, with the deliberation of earth processes that can afford to be slow because they have so much time for completion, the accumulation of the sediments has proceeded. So little in a year, or in a human lifetime, but so enormous an amount in the life of earth and sea.
The rains, the eroding away of the earth, the rush of sediment-laden waters have continued, with varying pulse and tempo, throughout all of geologic time. In addition to the silt load of every river that finds its way to the sea, there are other materials that compose the sediments. Volcanic dust, blown perhaps half way aro
und the earth in the upper atmosphere, comes eventually to rest on the ocean, drifts in the currents, becomes waterlogged, and sinks. Sands from coastal deserts are carried seaward on offshore winds, fall to the sea, and sink. Gravel, pebbles, small boulders, and shells are carried by icebergs and drift ice, to be released to the water when the ice melts. Fragments of iron, nickel, and other meteoric debris that enter the earth’s atmosphere over the sea—these, too, become flakes of the great snowfall. But most widely distributed of all are the billions upon billions of tiny shells and skeletons, the limy or silicious remains of all the minute creatures that once lived in the upper waters.
The sediments are a sort of epic poem of the earth. When we are wise enough, perhaps we can read in them all of past history. For all is written here. In the nature of the materials that compose them and in the arrangement of their successive layers the sediments reflect all that has happened in the waters above them and on the surrounding lands. The dramatic and the catastrophic in earth history have left their trace in the sediments—the outpourings of volcanoes, the advance and retreat of the ice, the searing aridity of desert lands, the sweeping destruction of floods.
The book of the sediments has been opened only within the lifetime of the present generation of scientists, with the most exciting progress in collecting and deciphering samples made since 1945. Early oceanographers could scrape up surface layers of sediment from the sea bottom with dredges. But what was needed was an instrument, operated on the principle of an apple corer, that could be driven vertically into the bottom to remove a long sample or ‘core’ in which the order of the different layers was undisturbed. Such an instrument was invented by Dr. C. S. Piggot in 1935, and with the aid of this ‘gun’ he obtained a series of cores across the deep Atlantic from Newfoundland to Ireland. These cores averaged about 10 feet long. A piston core sampler, developed by the Swedish oceanographer Kullenberg about 10 years later, now takes undisturbed cores 70 feet long. The rate of sedimentation in the different parts of the ocean is not definitely known, but it is very slow; certainly such a sample represents millions of years of geologic history.
The Sea Around Us Page 9